# eFuse Manager

[中文]

## Introduction

eFuse (Electronic Fuses) are microscopic one-time programmable fuses that can be "burned" (i.e., programmed) to store data into the ESP32-S2. eFuse bits are organized into different data fields, and these data fields could be used for system parameters (i.e., data parameters used by ESP-IDF of ESP32-S2) or user defined parameters.

The eFuse Manager component is a collection of tools and APIs that assist with defining, burning, accessing eFuses parameters. The notable tools and APIs include:

- A table format used to define eFuse data fields in CSV file.

- `efuse_table_gen.py` tool to generate C structure representation of eFuse data fields specified by the CSV file.

- Collection of C API to read/write eFuse data fields.

## eFuse Manager vs `idf.py`

`idf.py` provides a subset of the functionality of the eFuse Manager via the `idf.py efuse-<subcommand>` commands. In this documentation, mostly `idf.py` based commands will be used, although you can still see some `espefuse.py` based commands for advanced or rare cases. To see all available commands, run `idf.py --help` and search for those prefixed with `efuse-`.

## Hardware Description

The ESP32-S2 has a number of eFuses which can store system and user parameters. Each eFuse is a one-bit field which can be programmed to 1 after which it cannot be reverted back to 0. The eFuse bits are grouped into blocks of 256 bits, where each block is further divided into 8 32-bit registers. Some blocks are reserved for system parameters while the remaining blocks can be used for user parameters.

For more details, see ESP32-S2 Technical Reference Manual > eFuse Controller (eFuse) [PDF].

ESP32-S2 has 11 eFuse blocks each containing 256 bits (not all bits can be used for user parameters):

- EFUSE_BLK0 is used entirely for system parameters

- EFUSE_BLK1 is used entirely for system parameters

- EFUSE_BLK2 is used entirely for system parameters

- EFUSE_BLK3 (also named EFUSE_BLK_USER_DATA) can be used for user parameters

- EFUSE_BLK4 to EFUSE_BLK8 (also named EFUSE_BLK_KEY0 to EFUSE_BLK_KEY4) can be used to store keys for Secure Boot or Flash Encryption. If both features are unused, these blocks can be used for user parameters.

- EFUSE_BLK9 (also named EFUSE_BLK_KEY5) can be used to store keys for Secure Boot or Flash Encryption. If both features are unused, these blocks can be used for user parameters.

- EFUSE_BLK10 (also named EFUSE_BLK_SYS_DATA_PART2) is reserved for system parameters.

## Defining eFuse Fields

eFuse fields are defined as a table of records in a CSV file according to a specific format. This record format provides the ability to form eFuse fields of any length and from any number of individual bits.

Moreover, the record format allows structured definition of eFuse fields consisting of sub-fields, meaning that a parent eFuse field may consist of multiple child eFuse fields occupying the same eFuse bits.

### Record Format

In simple cases, each record occupies a single row in the table. Each record contains the following values (i.e., columns):

    # field_name, efuse_block(EFUSE_BLK0..EFUSE_BLK10), bit_start(0..255), bit_count(1..256), comment

- `field_name`

  > - Name of the eFuse field.

  > - The prefix `ESP_EFUSE_` is automatically added to the name, and this name will be used when referring to the field in C code.

  > - `field_name` unique across all eFuse fields.

  > - If this value is left empty, then this record is combined with the previous record. This allows you define an eFuse field with arbitrary bit ordering (see `MAC_FACTORY` field in the common table).

  > - Using `.` will define a child eFuse field. See Structured eFuse Fields for more details.

- `efuse_block`

  > - The eFuse field's block number. E.g., EFUSE_BLK0 to EFUSE_BLK10.

  > - This determines which block the eFuse field is placed.

- `bit_start`

  > - Bit offset (0 to 255) of the eFuse within the block.

  > - `bit_start` is optional and can be omitted.

  >   > - In this case, it is set to `bit_start + bit_count` from the previous record, given that the previous record is in the same eFuse block.

  >   > - If the previous record is in a different eFuse block, an error will be generated.

- `bit_count`

  > - The size of the eFuse field in bits (1 to N).

  > - `bit_count` cannot be omitted.

  > - If set to `MAX_BLK_LEN` the eFuse field's size will be the maximum allowable eFuse field size in the block.

- `comment`

  > - Comment describing the eFuse field.

  > - The comment is copied verbatim into the C header file.

If an eFuse field requires non-sequential bit ordering, then the eFuse field will span multiple records (i.e., multiple rows). The first record's `field_name` should specify the eFuse field's name, and the following records should leave `field_name` blank to indicate that they belong to the same eFuse field.

The following example demonstrates the records to specify the non-sequential eFuse field `MAC_FACTORY` followed by a regular eFuse field `MAC_FACTORY_CRC`:

    # Factory MAC address #
    #######################
    MAC_FACTORY,            EFUSE_BLK0,    72,    8,    Factory MAC addr [0]
    ,                       EFUSE_BLK0,    64,    8,    Factory MAC addr [1]
    ,                       EFUSE_BLK0,    56,    8,    Factory MAC addr [2]
    ,                       EFUSE_BLK0,    48,    8,    Factory MAC addr [3]
    ,                       EFUSE_BLK0,    40,    8,    Factory MAC addr [4]
    ,                       EFUSE_BLK0,    32,    8,    Factory MAC addr [5]
    MAC_FACTORY_CRC,        EFUSE_BLK0,    80,    8,    CRC8 for factory MAC address

This eFuse fields will be made available in C code as `ESP_EFUSE_MAC_FACTORY` and `ESP_EFUSE_MAC_FACTORY_CRC`.

## Structured eFuse Fields

Typically, an eFuse field represents a particular parameter. However, in some cases where an eFuse field consists of multiple sub-fields, it may be useful to have isolated access to those sub-fields. For example, if an eFuse field contained a floating point parameter, it may be useful to be access the sign, exponent, and mantissa fields of the floating as separate eFuse fields.

Therefore, it is possible for records to define eFuse fields in a structured manner using the `.` operator in `field_name`. For example, `XX.YY.ZZ` defines a eFuse field `ZZ` that is a child of eFuse field `YY` which in turn is a child field of eFuse field `XX`.

The following records demonstrate the definition of eFuse fields in a structured manner:

    WR_DIS,                           EFUSE_BLK0,   0,    32,     Write protection
    WR_DIS.RD_DIS,                    EFUSE_BLK0,   0,    1,      Write protection for RD_DIS
    WR_DIS.FIELD_1,                   EFUSE_BLK0,   1,    1,      Write protection for FIELD_1
    WR_DIS.FIELD_2,                   EFUSE_BLK0,   2,    4,      Write protection for FIELD_2 (includes B1 and B2)
    WR_DIS.FIELD_2.B1,                EFUSE_BLK0,   2,    2,      Write protection for FIELD_2.B1
    WR_DIS.FIELD_2.B2,                EFUSE_BLK0,   4,    2,      Write protection for FIELD_2.B2
    WR_DIS.FIELD_3,                   EFUSE_BLK0,   5,    1,      Write protection for FIELD_3
    WR_DIS.FIELD_3.ALIAS,             EFUSE_BLK0,   5,    1,      Write protection for FIELD_3 (just a alias for WR_DIS.FIELD_3)
    WR_DIS.FIELD_4,                   EFUSE_BLK0,   7,    1,      Write protection for FIELD_4

Some things to note regarding the example above:

- The `WR_DIS` record defines the parent eFuse field. All the other records are child fields of `WR_DIS` due to their `WR_DIS.` prefix.

- The child fields must utilize the same bits as their parent field. Take note of `bit_start` and `bit_count` of the child and parent fields:

  > - The bits of the child fields are always in the range of their parent field. For example, `WR_DIS.RD_DIS` and `WR_DIS.RD_DIS` occupy the first and second bit of `WR_DIS`.

  > - Child fields cannot use overlapping bits (except for when aliasing).

- It is possible to create aliases as a child field. For example, `WR_DIS.FIELD_3.ALIAS` is a child field and alias of `WR_DIS.FIELD_3` as they both occupy the same bits.

All eFuse Fields are eventually converted to C structures via the `efuse_table_gen.py` tool. The C structure for each eFuse field will derive their identifier from the `field_name` of the eFuse field's record, where all `.` are replaced with `_`. For example, the C symbols for `WR_DIS.RD_DIS` and `WR_DIS.FIELD_2.B1` will be `ESP_EFUSE_WR_DIS_RD_DIS` and `ESP_EFUSE_WR_DIS_FIELD_2_B1` respectively.

The `efuse_table_gen.py` tool also checks that the fields do not overlap each other and must be within the range of a field. If there is a violation, then the following error is generated:

    Field at USER_DATA, EFUSE_BLK3, 0, 256 intersected with SERIAL_NUMBER, EFUSE_BLK3, 0, 32

In this case, the error can be resolved by making `SERIAL_NUMBER` a child field of `USER_DATA` via `USER_DATA.SERIAL_NUMBER`.

    Field at FIELD, EFUSE_BLK3, 0, 50 out of range FIELD.MAJOR_NUMBER, EFUSE_BLK3, 60, 32

In this case, the error can be resolved by changing `bit_start` for `FIELD.MAJOR_NUMBER` from `60` to `0` so that `MAJOR_NUMBER` overlaps with `FIELD`.

## `efuse_table_gen.py` Tool

The `efuse_table_gen.py` tool is designed to generate C source files containing C structures (of type `esp_efuse_desc_t`) representing the eFuse fields defined in CSV files. Moreover, the tool also runs some checks on the provided CSV files before generation to ensure that:

- the names of the eFuse fields are unique

- the eFuse fields do not use overlapping bits

As mentioned previously, eFuse fields can be used to hold either system parameters or user parameters. Given that system parameter eFuse fields are inherently required by ESP-IDF and ESP32-S2, those eFuse fields are defined in a common CSV file (`esp_efuse_table.csv`) and distributed as part of ESP-IDF. For user parameter eFuse fields, users should define those fields in a custom CSV file (e.g., `esp_efuse_custom_table.csv`).

To generate C source files using the common CSV file, use the `idf.py efuse-common-table` or the following:

    cd $IDF_PATH/components/efuse/
    ./efuse_table_gen.py --idf_target esp32s2 esp32s2/esp_efuse_table.csv

The following C source/header files will be generated by the tool in `$IDF_PATH/components/efuse/esp32s2`:

- `esp_efuse_table.c` file containing the C structures of the system parameter eFuse fields

- `esp_efuse_table.h` file in the `include` folder. This header can be included by the application to use those C structures.

To generate C source files using a custom CSV file, use the command `idf.py efuse-custom-table` or the following:

    cd $IDF_PATH/components/efuse/
    ./efuse_table_gen.py --idf_target esp32s2 esp32s2/esp_efuse_table.csv PROJECT_PATH/main/esp_efuse_custom_table.csv

The following C source/header files will be generated by the tool in `PROJECT_PATH/main`:

- `esp_efuse_custom_table.c` file containing the C structures of the user parameter eFuse fields

- `esp_efuse_custom_table.h` file in the `include` folder. This header can be included by the application to use those C structures.

To use the generated fields, you need to include two files:

    #include "esp_efuse.h"
    #include "esp_efuse_table.h" // or "esp_efuse_custom_table.h"

## Supported Coding Schemes

Various coding schemes are supported by eFuses which can protect eFuses against data corruption by detecting and/or correcting for errors.

ESP32-S2 does not support selection of coding schemes. The following coding schemes are automatically applied to various eFuse blocks:

- `None`: Applied to EFUSE_BLK0

- `RS`: Applied to EFUSE_BLK1 - EFUSE_BLK10

### `None` Coding Scheme

The `None` coding scheme is automatically applied to EFUSE_BLK0. This scheme does not involve any encoding, but simply maintains four backups of EFUSE_BLK0 in hardware, meaning each bit is stored four times. As a result, EFUSE_BLK0 can be written many times.

This scheme is automatically applied by the hardware and is not visible to software.

### `RS` Coding Scheme

The `RS` coding scheme uses Reed-Solomon encoding and is automatically applied to EFUSE_BLK1 to EFUSE_BLK10. The coding scheme supports up to 6 bytes of automatic error correction.

Software encodes the 32-byte EFUSE_BLKx using `RS(44, 32)` to generate a 12-byte check-symbols, and then burn the EFUSE_BLKx and the check-symbols into eFuse at the same time.

The eFuse Controller automatically decodes the `RS` encoding and applies error correction when reading back the eFuse block. Because the `RS` check-symbols are generated across the entire 256-bit eFuse block, each block can only be written to one time. As a result of the check-symbols, Batch Writing Mode must be used.

### Batch Writing Mode

When writing to eFuse fields at run time, it may be necessary to use the Batch Writing Mode depending on the coding scheme used for eFuse block. Batch writing mode can be used as follows:

1. Enable batch writing mode by calling `esp_efuse_batch_write_begin()`

2. Write to the eFuse fields as usual using various `esp_efuse_write_...` functions.

3. Once all writes are complete, call `esp_efuse_batch_write_commit()` which burns prepared data to the eFuse blocks.

Warning

If there is already pre-written data in the eFuse block using the `Reed-Solomon` encoding scheme, then it is not possible to write anything extra (even if the required bits are empty) without breaking the previous data's checksums/check-symbols.

The checksums/check-symbols will be overwritten with new checksums/check-symbols and be completely destroyed (however, the payload eFuses are not damaged).

If you happen to find pre-written data in CUSTOM_MAC, SPI_PAD_CONFIG_HD, SPI_PAD_CONFIG_CS, etc., please contact Espressif to obtain the required pre-burnt eFuses.

FOR TESTING ONLY (NOT RECOMMENDED): You can ignore or suppress errors that violate encoding scheme data in order to burn the necessary bits in the eFuse block.

## eFuse API

Access to the fields is via a pointer to the description structure. API functions have some basic operation:

- `esp_efuse_read_field_blob()` - returns an array of read eFuse bits.

- `esp_efuse_read_field_cnt()` - returns the number of bits programmed as "1".

- `esp_efuse_write_field_blob()` - writes an array.

- `esp_efuse_write_field_cnt()` - writes a required count of bits as "1".

- `esp_efuse_get_field_size()` - returns the number of bits by the field name.

- `esp_efuse_read_reg()` - returns value of eFuse register.

- `esp_efuse_write_reg()` - writes value to eFuse register.

- `esp_efuse_get_coding_scheme()` - returns eFuse coding scheme for blocks.

- `esp_efuse_read_block()` - reads a key from an eFuse block starting at the offset with required size.

- `esp_efuse_write_block()` - writes a key to an eFuse block starting at the offset with required size.

- `esp_efuse_batch_write_begin()` - set the batch mode of writing fields.

- `esp_efuse_batch_write_commit()` - writes all prepared data for batch writing mode and reset the batch writing mode.

- `esp_efuse_batch_write_cancel()` - reset the batch writing mode and prepared data.

- `esp_efuse_get_key_dis_read()` - Returns a read protection for the key block.

- `esp_efuse_set_key_dis_read()` - Sets a read protection for the key block.

- `esp_efuse_get_key_dis_write()` - Returns a write protection for the key block.

- `esp_efuse_set_key_dis_write()` - Sets a write protection for the key block.

- `esp_efuse_get_key_purpose()` - Returns the current purpose set for an eFuse key block.

- `esp_efuse_write_key()` - Programs a block of key data to an eFuse block.

- `esp_efuse_write_keys()` - Programs keys to unused eFuse blocks.

- `esp_efuse_find_purpose()` - Finds a key block with the particular purpose set.

- `esp_efuse_get_keypurpose_dis_write()` - Returns a write protection of the key purpose field for an eFuse key block (for esp32 always true).

- `esp_efuse_key_block_unused()` - Returns true if the key block is unused, false otherwise.

- `esp_efuse_destroy_block()` - Destroys the data in this eFuse block. There are two things to do: (1) if write protection is not set, then the remaining unset bits are burned, (2) set read protection for this block if it is not locked.

For frequently used fields, special functions are made, like this `esp_efuse_get_pkg_ver()`.

## eFuse API for Keys

EFUSE_BLK_KEY0 - EFUSE_BLK_KEY5 are intended to keep up to 6 keys with a length of 256-bits. Each key has an `ESP_EFUSE_KEY_PURPOSE_x` field which defines the purpose of these keys. The purpose field is described in `esp_efuse_purpose_t`.

The purposes like `ESP_EFUSE_KEY_PURPOSE_XTS_AES_...` are used for flash encryption.

The purposes like `ESP_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST...` are used for secure boot.

There are some eFuse APIs useful to work with states of keys:

- `esp_efuse_get_purpose_field()` - Returns a pointer to a key purpose for an eFuse key block.

- `esp_efuse_get_key()` - Returns a pointer to a key block.

- `esp_efuse_set_key_purpose()` - Sets a key purpose for an eFuse key block.

- `esp_efuse_set_keypurpose_dis_write()` - Sets a write protection of the key purpose field for an eFuse key block.

- `esp_efuse_find_unused_key_block()` - Search for an unused key block and return the first one found.

- `esp_efuse_count_unused_key_blocks()` - Returns the number of unused eFuse key blocks in the range EFUSE_BLK_KEY0 to EFUSE_BLK_KEY_MAX

- `esp_efuse_get_digest_revoke()` - Returns the status of the Secure Boot public key digest revocation bit.

- `esp_efuse_set_digest_revoke()` - Sets the Secure Boot public key digest revocation bit.

- `esp_efuse_get_write_protect_of_digest_revoke()` - Returns a write protection of the Secure Boot public key digest revocation bit.

- `esp_efuse_set_write_protect_of_digest_revoke()` - Sets a write protection of the Secure Boot public key digest revocation bit.

## How to Add a New Field

1. Find free bits for field. Refer to the `esp_efuse_table.csv` file, running `idf.py show-efuse-table`, or running the following command:

    $ ./efuse_table_gen.py esp32s2/esp_efuse_table.csv --info

    Parsing efuse CSV input file $IDF_PATH/components/efuse/esp32s2/esp_efuse_table.csv ...
    Verifying efuse table...
    Max number of bits in BLK 256
    Sorted efuse table:
    #       field_name                      efuse_block     bit_start       bit_count
    1       WR_DIS                          EFUSE_BLK0         0               32
    2       WR_DIS.RD_DIS                   EFUSE_BLK0         0               1
    3       WR_DIS.DIS_ICACHE               EFUSE_BLK0         2               1
    4       WR_DIS.DIS_DCACHE               EFUSE_BLK0         2               1
    5       WR_DIS.DIS_DOWNLOAD_ICACHE      EFUSE_BLK0         2               1
    6       WR_DIS.DIS_DOWNLOAD_DCACHE      EFUSE_BLK0         2               1
    7       WR_DIS.DIS_FORCE_DOWNLOAD       EFUSE_BLK0         2               1
    8       WR_DIS.DIS_USB                  EFUSE_BLK0         2               1
    9       WR_DIS.DIS_TWAI                 EFUSE_BLK0         2               1
    10      WR_DIS.DIS_BOOT_REMAP           EFUSE_BLK0         2               1
    11      WR_DIS.SOFT_DIS_JTAG            EFUSE_BLK0         2               1
    12      WR_DIS.HARD_DIS_JTAG            EFUSE_BLK0         2               1
    13      WR_DIS.DIS_DOWNLOAD_MANUAL_ENCRYPT      EFUSE_BLK0         2               1
    14      WR_DIS.VDD_SPI_XPD              EFUSE_BLK0         3               1
    15      WR_DIS.VDD_SPI_TIEH             EFUSE_BLK0         3               1
    16      WR_DIS.VDD_SPI_FORCE            EFUSE_BLK0         3               1
    17      WR_DIS.WDT_DELAY_SEL            EFUSE_BLK0         3               1
    18      WR_DIS.SPI_BOOT_CRYPT_CNT       EFUSE_BLK0         4               1
    19      WR_DIS.SECURE_BOOT_KEY_REVOKE0  EFUSE_BLK0         5               1
    20      WR_DIS.SECURE_BOOT_KEY_REVOKE1  EFUSE_BLK0         6               1
    21      WR_DIS.SECURE_BOOT_KEY_REVOKE2  EFUSE_BLK0         7               1
    22      WR_DIS.KEY_PURPOSE_0            EFUSE_BLK0         8               1
    23      WR_DIS.KEY_PURPOSE_1            EFUSE_BLK0         9               1
    24      WR_DIS.KEY_PURPOSE_2            EFUSE_BLK0         10              1
    25      WR_DIS.KEY_PURPOSE_3            EFUSE_BLK0         11              1
    26      WR_DIS.KEY_PURPOSE_4            EFUSE_BLK0         12              1
    27      WR_DIS.KEY_PURPOSE_5            EFUSE_BLK0         13              1
    28      WR_DIS.SECURE_BOOT_EN           EFUSE_BLK0         15              1
    29      WR_DIS.SECURE_BOOT_AGGRESSIVE_REVOKE    EFUSE_BLK0         16              1
    30      WR_DIS.FLASH_TPUW               EFUSE_BLK0         18              1
    31      WR_DIS.DIS_DOWNLOAD_MODE        EFUSE_BLK0         18              1
    32      WR_DIS.DIS_LEGACY_SPI_BOOT      EFUSE_BLK0         18              1
    33      WR_DIS.UART_PRINT_CHANNEL       EFUSE_BLK0         18              1
    34      WR_DIS.DIS_USB_DOWNLOAD_MODE    EFUSE_BLK0         18              1
    35      WR_DIS.ENABLE_SECURITY_DOWNLOAD         EFUSE_BLK0         18              1
    36      WR_DIS.UART_PRINT_CONTROL       EFUSE_BLK0         18              1
    37      WR_DIS.PIN_POWER_SELECTION      EFUSE_BLK0         18              1
    38      WR_DIS.FLASH_TYPE               EFUSE_BLK0         18              1
    39      WR_DIS.FORCE_SEND_RESUME        EFUSE_BLK0         18              1
    40      WR_DIS.SECURE_VERSION           EFUSE_BLK0         18              1
    41      WR_DIS.BLK1                     EFUSE_BLK0         20              1
    42      WR_DIS.MAC                      EFUSE_BLK0         20              1
    43      WR_DIS.SPI_PAD_CONFIG_CLK       EFUSE_BLK0         20              1
    44      WR_DIS.SPI_PAD_CONFIG_Q         EFUSE_BLK0         20              1
    45      WR_DIS.SPI_PAD_CONFIG_D         EFUSE_BLK0         20              1
    46      WR_DIS.SPI_PAD_CONFIG_CS        EFUSE_BLK0         20              1
    47      WR_DIS.SPI_PAD_CONFIG_HD        EFUSE_BLK0         20              1
    48      WR_DIS.SPI_PAD_CONFIG_WP        EFUSE_BLK0         20              1
    49      WR_DIS.SPI_PAD_CONFIG_DQS       EFUSE_BLK0         20              1
    50      WR_DIS.SPI_PAD_CONFIG_D4        EFUSE_BLK0         20              1
    51      WR_DIS.SPI_PAD_CONFIG_D5        EFUSE_BLK0         20              1
    52      WR_DIS.SPI_PAD_CONFIG_D6        EFUSE_BLK0         20              1
    53      WR_DIS.SPI_PAD_CONFIG_D7        EFUSE_BLK0         20              1
    54      WR_DIS.WAFER_VERSION_MAJOR      EFUSE_BLK0         20              1
    55      WR_DIS.WAFER_VERSION_MINOR_HI   EFUSE_BLK0         20              1
    56      WR_DIS.FLASH_VERSION            EFUSE_BLK0         20              1
    57      WR_DIS.BLK_VERSION_MAJOR        EFUSE_BLK0         20              1
    58      WR_DIS.PSRAM_VERSION            EFUSE_BLK0         20              1
    59      WR_DIS.PKG_VERSION              EFUSE_BLK0         20              1
    60      WR_DIS.WAFER_VERSION_MINOR_LO   EFUSE_BLK0         20              1
    61      WR_DIS.SYS_DATA_PART1           EFUSE_BLK0         21              1
    62      WR_DIS.OPTIONAL_UNIQUE_ID       EFUSE_BLK0         21              1
    63      WR_DIS.ADC_CALIB                EFUSE_BLK0         21              1
    64      WR_DIS.BLK_VERSION_MINOR        EFUSE_BLK0         21              1
    65      WR_DIS.TEMP_CALIB               EFUSE_BLK0         21              1
    66      WR_DIS.RTCCALIB_V1IDX_A10H      EFUSE_BLK0         21              1
    67      WR_DIS.RTCCALIB_V1IDX_A11H      EFUSE_BLK0         21              1
    68      WR_DIS.RTCCALIB_V1IDX_A12H      EFUSE_BLK0         21              1
    69      WR_DIS.RTCCALIB_V1IDX_A13H      EFUSE_BLK0         21              1
    70      WR_DIS.RTCCALIB_V1IDX_A20H      EFUSE_BLK0         21              1
    71      WR_DIS.RTCCALIB_V1IDX_A21H      EFUSE_BLK0         21              1
    72      WR_DIS.RTCCALIB_V1IDX_A22H      EFUSE_BLK0         21              1
    73      WR_DIS.RTCCALIB_V1IDX_A23H      EFUSE_BLK0         21              1
    74      WR_DIS.RTCCALIB_V1IDX_A10L      EFUSE_BLK0         21              1
    75      WR_DIS.RTCCALIB_V1IDX_A11L      EFUSE_BLK0         21              1
    76      WR_DIS.RTCCALIB_V1IDX_A12L      EFUSE_BLK0         21              1
    77      WR_DIS.RTCCALIB_V1IDX_A13L      EFUSE_BLK0         21              1
    78      WR_DIS.RTCCALIB_V1IDX_A20L      EFUSE_BLK0         21              1
    79      WR_DIS.RTCCALIB_V1IDX_A21L      EFUSE_BLK0         21              1
    80      WR_DIS.RTCCALIB_V1IDX_A22L      EFUSE_BLK0         21              1
    81      WR_DIS.RTCCALIB_V1IDX_A23L      EFUSE_BLK0         21              1
    82      WR_DIS.BLOCK_USR_DATA           EFUSE_BLK0         22              1
    83      WR_DIS.CUSTOM_MAC               EFUSE_BLK0         22              1
    84      WR_DIS.BLOCK_KEY0               EFUSE_BLK0         23              1
    85      WR_DIS.BLOCK_KEY1               EFUSE_BLK0         24              1
    86      WR_DIS.BLOCK_KEY2               EFUSE_BLK0         25              1
    87      WR_DIS.BLOCK_KEY3               EFUSE_BLK0         26              1
    88      WR_DIS.BLOCK_KEY4               EFUSE_BLK0         27              1
    89      WR_DIS.BLOCK_KEY5               EFUSE_BLK0         28              1
    90      WR_DIS.BLOCK_SYS_DATA2          EFUSE_BLK0         29              1
    91      WR_DIS.USB_EXCHG_PINS           EFUSE_BLK0         30              1
    92      WR_DIS.USB_EXT_PHY_ENABLE       EFUSE_BLK0         30              1
    93      WR_DIS.USB_FORCE_NOPERSIST      EFUSE_BLK0         30              1
    94      WR_DIS.BLOCK0_VERSION           EFUSE_BLK0         30              1
    95      RD_DIS                          EFUSE_BLK0         32              7
    96      RD_DIS.BLOCK_KEY0               EFUSE_BLK0         32              1
    97      RD_DIS.BLOCK_KEY1               EFUSE_BLK0         33              1
    98      RD_DIS.BLOCK_KEY2               EFUSE_BLK0         34              1
    99      RD_DIS.BLOCK_KEY3               EFUSE_BLK0         35              1
    100     RD_DIS.BLOCK_KEY4               EFUSE_BLK0         36              1
    101     RD_DIS.BLOCK_KEY5               EFUSE_BLK0         37              1
    102     RD_DIS.BLOCK_SYS_DATA2          EFUSE_BLK0         38              1
    103     DIS_ICACHE                      EFUSE_BLK0         40              1
    104     DIS_DCACHE                      EFUSE_BLK0         41              1
    105     DIS_DOWNLOAD_ICACHE             EFUSE_BLK0         42              1
    106     DIS_DOWNLOAD_DCACHE             EFUSE_BLK0         43              1
    107     DIS_FORCE_DOWNLOAD              EFUSE_BLK0         44              1
    108     DIS_USB                         EFUSE_BLK0         45              1
    109     DIS_TWAI                        EFUSE_BLK0         46              1
    110     DIS_BOOT_REMAP                  EFUSE_BLK0         47              1
    111     SOFT_DIS_JTAG                   EFUSE_BLK0         49              1
    112     HARD_DIS_JTAG                   EFUSE_BLK0         50              1
    113     DIS_DOWNLOAD_MANUAL_ENCRYPT     EFUSE_BLK0         51              1
    114     USB_EXCHG_PINS                  EFUSE_BLK0         56              1
    115     USB_EXT_PHY_ENABLE              EFUSE_BLK0         57              1
    116     USB_FORCE_NOPERSIST             EFUSE_BLK0         58              1
    117     BLOCK0_VERSION                  EFUSE_BLK0         59              2
    118     VDD_SPI_XPD                     EFUSE_BLK0         68              1
    119     VDD_SPI_TIEH                    EFUSE_BLK0         69              1
    120     VDD_SPI_FORCE                   EFUSE_BLK0         70              1
    121     WDT_DELAY_SEL                   EFUSE_BLK0         80              2
    122     SPI_BOOT_CRYPT_CNT              EFUSE_BLK0         82              3
    123     SECURE_BOOT_KEY_REVOKE0         EFUSE_BLK0         85              1
    124     SECURE_BOOT_KEY_REVOKE1         EFUSE_BLK0         86              1
    125     SECURE_BOOT_KEY_REVOKE2         EFUSE_BLK0         87              1
    126     KEY_PURPOSE_0                   EFUSE_BLK0         88              4
    127     KEY_PURPOSE_1                   EFUSE_BLK0         92              4
    128     KEY_PURPOSE_2                   EFUSE_BLK0         96              4
    129     KEY_PURPOSE_3                   EFUSE_BLK0        100              4
    130     KEY_PURPOSE_4                   EFUSE_BLK0        104              4
    131     KEY_PURPOSE_5                   EFUSE_BLK0        108              4
    132     SECURE_BOOT_EN                  EFUSE_BLK0        116              1
    133     SECURE_BOOT_AGGRESSIVE_REVOKE   EFUSE_BLK0        117              1
    134     FLASH_TPUW                      EFUSE_BLK0        124              4
    135     DIS_DOWNLOAD_MODE               EFUSE_BLK0        128              1
    136     DIS_LEGACY_SPI_BOOT             EFUSE_BLK0        129              1
    137     UART_PRINT_CHANNEL              EFUSE_BLK0        130              1
    138     DIS_USB_DOWNLOAD_MODE           EFUSE_BLK0        132              1
    139     ENABLE_SECURITY_DOWNLOAD        EFUSE_BLK0        133              1
    140     UART_PRINT_CONTROL              EFUSE_BLK0        134              2
    141     PIN_POWER_SELECTION             EFUSE_BLK0        136              1
    142     FLASH_TYPE                      EFUSE_BLK0        137              1
    143     FORCE_SEND_RESUME               EFUSE_BLK0        138              1
    144     SECURE_VERSION                  EFUSE_BLK0        139              16
    145     DISABLE_WAFER_VERSION_MAJOR     EFUSE_BLK0        160              1
    146     DISABLE_BLK_VERSION_MAJOR       EFUSE_BLK0        161              1
    147     MAC                             EFUSE_BLK1         0               8
    148     MAC                             EFUSE_BLK1         8               8
    149     MAC                             EFUSE_BLK1         16              8
    150     MAC                             EFUSE_BLK1         24              8
    151     MAC                             EFUSE_BLK1         32              8
    152     MAC                             EFUSE_BLK1         40              8
    153     SPI_PAD_CONFIG_CLK              EFUSE_BLK1         48              6
    154     SPI_PAD_CONFIG_Q                EFUSE_BLK1         54              6
    155     SPI_PAD_CONFIG_D                EFUSE_BLK1         60              6
    156     SPI_PAD_CONFIG_CS               EFUSE_BLK1         66              6
    157     SPI_PAD_CONFIG_HD               EFUSE_BLK1         72              6
    158     SPI_PAD_CONFIG_WP               EFUSE_BLK1         78              6
    159     SPI_PAD_CONFIG_DQS              EFUSE_BLK1         84              6
    160     SPI_PAD_CONFIG_D4               EFUSE_BLK1         90              6
    161     SPI_PAD_CONFIG_D5               EFUSE_BLK1         96              6
    162     SPI_PAD_CONFIG_D6               EFUSE_BLK1        102              6
    163     SPI_PAD_CONFIG_D7               EFUSE_BLK1        108              6
    164     WAFER_VERSION_MAJOR             EFUSE_BLK1        114              2
    165     WAFER_VERSION_MINOR_HI          EFUSE_BLK1        116              1
    166     FLASH_VERSION                   EFUSE_BLK1        117              4
    167     BLK_VERSION_MAJOR               EFUSE_BLK1        121              2
    168     PSRAM_VERSION                   EFUSE_BLK1        124              4
    169     PKG_VERSION                     EFUSE_BLK1        128              4
    170     WAFER_VERSION_MINOR_LO          EFUSE_BLK1        132              3
    171     SYS_DATA_PART2                  EFUSE_BLK10        0              256
    172     OPTIONAL_UNIQUE_ID              EFUSE_BLK2         0              128
    173     ADC_CALIB                       EFUSE_BLK2        128              4
    174     BLK_VERSION_MINOR               EFUSE_BLK2        132              3
    175     TEMP_CALIB                      EFUSE_BLK2        135              9
    176     RTCCALIB_V1IDX_A10H             EFUSE_BLK2        144              8
    177     RTCCALIB_V1IDX_A11H             EFUSE_BLK2        152              8
    178     RTCCALIB_V1IDX_A12H             EFUSE_BLK2        160              8
    179     RTCCALIB_V1IDX_A13H             EFUSE_BLK2        168              8
    180     RTCCALIB_V1IDX_A20H             EFUSE_BLK2        176              8
    181     RTCCALIB_V1IDX_A21H             EFUSE_BLK2        184              8
    182     RTCCALIB_V1IDX_A22H             EFUSE_BLK2        192              8
    183     RTCCALIB_V1IDX_A23H             EFUSE_BLK2        200              8
    184     RTCCALIB_V1IDX_A10L             EFUSE_BLK2        208              6
    185     RTCCALIB_V1IDX_A11L             EFUSE_BLK2        214              6
    186     RTCCALIB_V1IDX_A12L             EFUSE_BLK2        220              6
    187     RTCCALIB_V1IDX_A13L             EFUSE_BLK2        226              6
    188     RTCCALIB_V1IDX_A20L             EFUSE_BLK2        232              6
    189     RTCCALIB_V1IDX_A21L             EFUSE_BLK2        238              6
    190     RTCCALIB_V1IDX_A22L             EFUSE_BLK2        244              6
    191     RTCCALIB_V1IDX_A23L             EFUSE_BLK2        250              6
    192     USER_DATA                       EFUSE_BLK3         0              256
    193     USER_DATA.MAC_CUSTOM            EFUSE_BLK3        200              48
    194     KEY0                            EFUSE_BLK4         0              256
    195     KEY1                            EFUSE_BLK5         0              256
    196     KEY2                            EFUSE_BLK6         0              256
    197     KEY3                            EFUSE_BLK7         0              256
    198     KEY4                            EFUSE_BLK8         0              256
    199     KEY5                            EFUSE_BLK9         0              256

    Used bits in efuse table:
    EFUSE_BLK0
    [0 31] [0 0] [2 2] ... [32 38] [40 47] [49 51] [56 60] [68 70] [80 111] [116 117] [124 130] [132 154] [160 161]
    EFUSE_BLK1
    [0 122] [124 134]
    EFUSE_BLK10
    [0 255]
    EFUSE_BLK2
    [0 255]
    EFUSE_BLK3
    [0 255] [200 247]
    EFUSE_BLK4
    [0 255]
    EFUSE_BLK5
    [0 255]
    EFUSE_BLK6
    [0 255]
    EFUSE_BLK7
    [0 255]
    EFUSE_BLK8
    [0 255]
    EFUSE_BLK9
    [0 255]
    Note: Not printed ranges are free for using. (bits in EFUSE_BLK0 are reserved for Espressif)

The number of bits not included in square brackets are free (some bits are reserved by Espressif). All fields are checked for overlapping bits.

To add child fields to an existing field, Structured eFuse Fields can be used. The following example demonstrates adding of the the fields `SERIAL_NUMBER`, `MODEL_NUMBER` and `HARDWARE_REV` to an existing `USER_DATA` field by using the `.` operator:

    USER_DATA.SERIAL_NUMBER,                  EFUSE_BLK3,    0,  32,
    USER_DATA.MODEL_NUMBER,                   EFUSE_BLK3,    32, 10,
    USER_DATA.HARDWARE_REV,                   EFUSE_BLK3,    42, 10,

In general, to add new eFuse Fields:

1. Add a record for each eFuse field in CSV file.

2. Run the `show_efuse_table` command to check eFuse table.

3. To generate source files run the `efuse_common_table` or `efuse_custom_table` commands.

You may get errors such as `intersects with` or `out of range`. Please see how to solve them in the Structured eFuse Fields article.

## Bit Order

The eFuses bit order is little endian (see the example below), meaning that eFuse bits are read and written from LSB to MSB:

    $ idf.py efuse-dump

    USER_DATA      (BLOCK3          ) [3 ] read_regs: 03020100 07060504 0B0A0908 0F0E0D0C 13121111 17161514 1B1A1918 1F1E1D1C
    BLOCK4         (BLOCK4          ) [4 ] read_regs: 03020100 07060504 0B0A0908 0F0E0D0C 13121111 17161514 1B1A1918 1F1E1D1C

    where is the register representation:

    EFUSE_RD_USR_DATA0_REG = 0x03020100
    EFUSE_RD_USR_DATA1_REG = 0x07060504
    EFUSE_RD_USR_DATA2_REG = 0x0B0A0908
    EFUSE_RD_USR_DATA3_REG = 0x0F0E0D0C
    EFUSE_RD_USR_DATA4_REG = 0x13121111
    EFUSE_RD_USR_DATA5_REG = 0x17161514
    EFUSE_RD_USR_DATA6_REG = 0x1B1A1918
    EFUSE_RD_USR_DATA7_REG = 0x1F1E1D1C

    where is the byte representation:

    byte[0] = 0x00, byte[1] = 0x01, ... byte[3] = 0x03, byte[4] = 0x04, ..., byte[31] = 0x1F

For example, CSV file describes the `USER_DATA` field, which occupies all 256 bits (a whole block).

    USER_DATA,          EFUSE_BLK3,    0,  256,     User data
    USER_DATA.FIELD1,   EFUSE_BLK3,    16,  16,     Field1

    ID,                 EFUSE_BLK4,    8,  3,      ID bit[0..2]
    ,                   EFUSE_BLK4,    16, 2,      ID bit[3..4]
    ,                   EFUSE_BLK4,    32, 3,      ID bit[5..7]

Thus, reading the eFuse `USER_DATA` block written as above gives the following results:

    uint8_t buf[32] = { 0 };
    esp_efuse_read_field_blob(ESP_EFUSE_USER_DATA, &buf, sizeof(buf) * 8);
    // buf[0] = 0x00, buf[1] = 0x01, ... buf[31] = 0x1F

    uint32_t field1 = 0;
    size_t field1_size = ESP_EFUSE_USER_DATA[0]->bit_count; // can be used for this case because it only consists of one entry
    esp_efuse_read_field_blob(ESP_EFUSE_USER_DATA, &field1, field1_size);
    // field1 = 0x0302

    uint32_t field1_1 = 0;
    esp_efuse_read_field_blob(ESP_EFUSE_USER_DATA, &field1_1, 2); // reads only first 2 bits
    // field1 = 0x0002

    uint8_t id = 0;
    size_t id_size = esp_efuse_get_field_size(ESP_EFUSE_ID); // returns 6
    // size_t id_size = ESP_EFUSE_USER_DATA[0]->bit_count; // cannot be used because it consists of 3 entries. It returns 3 not 6
    esp_efuse_read_field_blob(ESP_EFUSE_ID, &id, id_size);
    // id = 0x91
    // b'100 10  001
    //   [3] [2] [3]

    uint8_t id_1 = 0;
    esp_efuse_read_field_blob(ESP_EFUSE_ID, &id_1, 3);
    // id = 0x01
    // b'001

## Get eFuses During Build

There is a way to get the state of eFuses at the build stage of the project. There are two CMake functions for this:

- `espefuse_get_json_summary()` - It calls the `espefuse.py summary --format json` command and returns a JSON string (it is not stored in a file).

- `espefuse_get_efuse()` - It finds a given eFuse name in the JSON string and returns its property.

The JSON string has the following properties:

    {
        "MAC": {
            "bit_len": 48,
            "block": 0,
            "category": "identity",
            "description": "Factory MAC Address",
            "efuse_type": "bytes:6",
            "name": "MAC",
            "pos": 0,
            "readable": true,
            "value": "94:b9:7e:5a:6e:58 (CRC 0xe2 OK)",
            "word": 1,
            "writeable": true
        },
    }

These functions can be used from a top-level project `CMakeLists.txt` (system/efuse/CMakeLists.txt):

    # ...
    project(hello_world)

    espefuse_get_json_summary(efuse_json)
    espefuse_get_efuse(ret_data ${efuse_json} "MAC" "value")
    message("MAC:" ${ret_data})

The format of the `value` property is the same as shown in `espefuse.py summary` or `idf.py efuse-summary`.

    MAC:94:b9:7e:5a:6e:58 (CRC 0xe2 OK)

There is an example test system/efuse/CMakeLists.txt which adds a custom target `efuse-filter`. This allows you to run the `idf.py efuse-filter` command to read the required eFuses (specified in the `efuse_names` list) at any time, not just during the project build.

## Debug eFuse & Unit Tests

### Virtual eFuses

The Kconfig option CONFIG_EFUSE_VIRTUAL virtualizes eFuse values inside the eFuse Manager, so writes are emulated and no eFuse values are permanently changed. This can be useful for debugging and unit testing.

During startup, the eFuses are copied to RAM. All eFuse operations (read and write) are performed with RAM instead of the real eFuse registers.

In addition to the CONFIG_EFUSE_VIRTUAL option, there is the CONFIG_EFUSE_VIRTUAL_KEEP_IN_FLASH option that adds a feature to keep eFuses in flash memory. To use this mode, the partition_table should have include an `efuse` partition in `partition.csv`:

    efuse_em, data, efuse,   ,   0x2000,

During startup, the eFuses are copied from flash, or in case where flash is empty, copied from real eFuse to RAM and then write flash. This option allows keeping eFuses after reboots, making it possible to test Secure Boot and Flash Encryption features.

#### Flash Encryption Testing

Flash encryption is a hardware feature that requires the physical burning of eFuses `key` and `FLASH_CRYPT_CNT`. If flash encryption is not actually enabled, then enabling the CONFIG_EFUSE_VIRTUAL_KEEP_IN_FLASH option just provides testing possibilities and does not encrypt anything in the flash, even though the logs indicates that encryption happens.

The `bootloader_flash_write()` is adapted for this purpose. But if flash encryption is already enabled on the chip when the application is run, or if the bootloader is created with the CONFIG_EFUSE_VIRTUAL_KEEP_IN_FLASH option, then the flash encryption/decryption operations will work properly. This means that data are encrypted as it is written into an encrypted flash partition and decrypted when they are read from an encrypted partition.

### `espefuse.py`

esptool includes a useful tool for reading/writing ESP32-S2 eFuse bits - espefuse.py.

Part of the functionality of this tool is also provided directly by `idf.py` commands. For example, the `idf.py efuse-summary` command is equivalent to `espefuse.py summary`.

    idf.py efuse-summary

    Executing action: efuse-summary
    "ninja efuse-summary"...

    (...)

    EFUSE_NAME (Block) Description  = [Meaningful Value] [Readable/Writeable] (Hex Value)
    ----------------------------------------------------------------------------------------
    Config fuses:
    WR_DIS (BLOCK0)                                    Disable programming of individual eFuses           = 0 R/W (0x00000000)
    RD_DIS (BLOCK0)                                    Disable reading from BlOCK4-10                     = 0 R/W (0b0000000)
    DIS_ICACHE (BLOCK0)                                Set this bit to disable Icache                     = False R/W (0b0)
    DIS_DCACHE (BLOCK0)                                Set this bit to disable Dcache                     = False R/W (0b0)
    DIS_TWAI (BLOCK0)                                  Set this bit to disable the TWAI Controller functi = False R/W (0b0)
                                                       on
    DIS_BOOT_REMAP (BLOCK0)                            Disables capability to Remap RAM to ROM address sp = False R/W (0b0)
                                                       ace
    DIS_LEGACY_SPI_BOOT (BLOCK0)                       Set this bit to disable Legacy SPI boot mode       = False R/W (0b0)
    UART_PRINT_CHANNEL (BLOCK0)                        Selects the default UART for printing boot message = UART0 R/W (0b0)
                                                       s
    UART_PRINT_CONTROL (BLOCK0)                        Set the default UART boot message output mode      = Enable R/W (0b00)
    PIN_POWER_SELECTION (BLOCK0)                       Set default power supply for GPIO33-GPIO37; set wh = VDD3P3_CPU R/W (0b0)
                                                       en SPI flash is initialized
    BLOCK_USR_DATA (BLOCK3)                            User data
       = 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 R/W
    BLOCK_SYS_DATA2 (BLOCK10)                          System data part 2 (reserved)
       = 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 R/W

    Flash fuses:
    FLASH_TPUW (BLOCK0)                                Configures flash startup delay after SoC power-up; = 0 R/W (0x0)
                                                        in unit of (ms/2). When the value is 15; delay is
                                                        7.5 ms
    FLASH_TYPE (BLOCK0)                                SPI flash type                                     = 4 data lines R/W (0b0)
    FORCE_SEND_RESUME (BLOCK0)                         If set; forces ROM code to send an SPI flash resum = False R/W (0b0)
                                                       e command during SPI boot
    FLASH_VERSION (BLOCK1)                             Flash version                                      = 2 R/W (0x2)

    Identity fuses:
    BLOCK0_VERSION (BLOCK0)                            BLOCK0 efuse version                               = 0 R/W (0b00)
    DISABLE_WAFER_VERSION_MAJOR (BLOCK0)               Disables check of wafer version major              = False R/W (0b0)
    DISABLE_BLK_VERSION_MAJOR (BLOCK0)                 Disables check of blk version major                = False R/W (0b0)
    WAFER_VERSION_MAJOR (BLOCK1)                       WAFER_VERSION_MAJOR                                = 1 R/W (0b01)
    WAFER_VERSION_MINOR_HI (BLOCK1)                    WAFER_VERSION_MINOR most significant bit           = False R/W (0b0)
    BLK_VERSION_MAJOR (BLOCK1)                         BLK_VERSION_MAJOR                                  = 0 R/W (0b00)
    PSRAM_VERSION (BLOCK1)                             PSRAM version                                      = 1 R/W (0x1)
    PKG_VERSION (BLOCK1)                               Package version                                    = 0 R/W (0x0)
    WAFER_VERSION_MINOR_LO (BLOCK1)                    WAFER_VERSION_MINOR least significant bits         = 0 R/W (0b000)
    OPTIONAL_UNIQUE_ID (BLOCK2)                        Optional unique 128-bit ID
       = ea 0e c6 f1 01 f2 38 82 e9 98 5b 59 81 fe 00 02 R/W
    BLK_VERSION_MINOR (BLOCK2)                         BLK_VERSION_MINOR of BLOCK2                        = ADC calib V2 R/W (0b010)
    WAFER_VERSION_MINOR (BLOCK0)                       calc WAFER VERSION MINOR = WAFER_VERSION_MINOR_HI  = 0 R/W (0x0)
                                                       << 3 + WAFER_VERSION_MINOR_LO (read only)

    Jtag fuses:
    SOFT_DIS_JTAG (BLOCK0)                             Software disables JTAG. When software disabled; JT = False R/W (0b0)
                                                       AG can be activated temporarily by HMAC peripheral
    HARD_DIS_JTAG (BLOCK0)                             Hardware disables JTAG permanently                 = False R/W (0b0)

    Mac fuses:
    MAC (BLOCK1)                                       MAC address
       = 58:cf:79:b3:b9:54 (OK) R/W
    CUSTOM_MAC (BLOCK3)                                Custom MAC
       = 00:00:00:00:00:00 (OK) R/W

    Security fuses:
    DIS_DOWNLOAD_ICACHE (BLOCK0)                       Disables Icache when SoC is in Download mode       = False R/W (0b0)
    DIS_DOWNLOAD_DCACHE (BLOCK0)                       Disables Dcache when SoC is in Download mode       = False R/W (0b0)
    DIS_FORCE_DOWNLOAD (BLOCK0)                        Set this bit to disable the function that forces c = False R/W (0b0)
                                                       hip into download mode
    DIS_DOWNLOAD_MANUAL_ENCRYPT (BLOCK0)               Disables flash encryption when in download boot mo = False R/W (0b0)
                                                       des
    SPI_BOOT_CRYPT_CNT (BLOCK0)                        Enables flash encryption when 1 or 3 bits are set  = Disable R/W (0b000)
                                                       and disabled otherwise
    SECURE_BOOT_KEY_REVOKE0 (BLOCK0)                   Revoke 1st secure boot key                         = False R/W (0b0)
    SECURE_BOOT_KEY_REVOKE1 (BLOCK0)                   Revoke 2nd secure boot key                         = False R/W (0b0)
    SECURE_BOOT_KEY_REVOKE2 (BLOCK0)                   Revoke 3rd secure boot key                         = False R/W (0b0)
    KEY_PURPOSE_0 (BLOCK0)                             Purpose of KEY0                                    = USER R/W (0x0)
    KEY_PURPOSE_1 (BLOCK0)                             Purpose of KEY1                                    = USER R/W (0x0)
    KEY_PURPOSE_2 (BLOCK0)                             Purpose of KEY2                                    = USER R/W (0x0)
    KEY_PURPOSE_3 (BLOCK0)                             Purpose of KEY3                                    = USER R/W (0x0)
    KEY_PURPOSE_4 (BLOCK0)                             Purpose of KEY4                                    = USER R/W (0x0)
    KEY_PURPOSE_5 (BLOCK0)                             Purpose of KEY5                                    = USER R/W (0x0)
    SECURE_BOOT_EN (BLOCK0)                            Set this bit to enable secure boot                 = False R/W (0b0)
    SECURE_BOOT_AGGRESSIVE_REVOKE (BLOCK0)             Set this bit to enable aggressive secure boot key  = False R/W (0b0)
                                                       revocation mode
    DIS_DOWNLOAD_MODE (BLOCK0)                         Set this bit to disable all download boot modes    = False R/W (0b0)
    ENABLE_SECURITY_DOWNLOAD (BLOCK0)                  Set this bit to enable secure UART download mode ( = False R/W (0b0)
                                                       read/write flash only)
    SECURE_VERSION (BLOCK0)                            Secure version (used by ESP-IDF anti-rollback      = 0 R/W (0x0000)
                                                       feature)
    BLOCK_KEY0 (BLOCK4)
      Purpose: USER
                   Key0 or user data
       = 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 R/W
    BLOCK_KEY1 (BLOCK5)
      Purpose: USER
                   Key1 or user data
       = 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 R/W
    BLOCK_KEY2 (BLOCK6)
      Purpose: USER
                   Key2 or user data
       = 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 R/W
    BLOCK_KEY3 (BLOCK7)
      Purpose: USER
                   Key3 or user data
       = 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 R/W
    BLOCK_KEY4 (BLOCK8)
      Purpose: USER
                   Key4 or user data
       = 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 R/W
    BLOCK_KEY5 (BLOCK9)
      Purpose: USER
                   Key5 or user data
       = 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 R/W

    Spi Pad fuses:
    SPI_PAD_CONFIG_CLK (BLOCK1)                        SPI_PAD_configure CLK                              = 0 R/W (0b000000)
    SPI_PAD_CONFIG_Q (BLOCK1)                          SPI_PAD_configure Q(D1)                            = 0 R/W (0b000000)
    SPI_PAD_CONFIG_D (BLOCK1)                          SPI_PAD_configure D(D0)                            = 0 R/W (0b000000)
    SPI_PAD_CONFIG_CS (BLOCK1)                         SPI_PAD_configure CS                               = 0 R/W (0b000000)
    SPI_PAD_CONFIG_HD (BLOCK1)                         SPI_PAD_configure HD(D3)                           = 0 R/W (0b000000)
    SPI_PAD_CONFIG_WP (BLOCK1)                         SPI_PAD_configure WP(D2)                           = 0 R/W (0b000000)
    SPI_PAD_CONFIG_DQS (BLOCK1)                        SPI_PAD_configure DQS                              = 0 R/W (0b000000)
    SPI_PAD_CONFIG_D4 (BLOCK1)                         SPI_PAD_configure D4                               = 0 R/W (0b000000)
    SPI_PAD_CONFIG_D5 (BLOCK1)                         SPI_PAD_configure D5                               = 0 R/W (0b000000)
    SPI_PAD_CONFIG_D6 (BLOCK1)                         SPI_PAD_configure D6                               = 0 R/W (0b000000)
    SPI_PAD_CONFIG_D7 (BLOCK1)                         SPI_PAD_configure D7                               = 0 R/W (0b000000)

    Usb fuses:
    DIS_USB (BLOCK0)                                   Set this bit to disable USB OTG function           = False R/W (0b0)
    USB_EXCHG_PINS (BLOCK0)                            Set this bit to exchange USB D+ and D- pins        = False R/W (0b0)
    USB_EXT_PHY_ENABLE (BLOCK0)                        Set this bit to enable external USB PHY            = False R/W (0b0)
    USB_FORCE_NOPERSIST (BLOCK0)                       If set; forces USB BVALID to 1                     = False R/W (0b0)
    DIS_USB_DOWNLOAD_MODE (BLOCK0)                     Set this bit to disable use of USB OTG in UART dow = False R/W (0b0)
                                                       nload boot mode

    Vdd fuses:
    VDD_SPI_XPD (BLOCK0)                               If VDD_SPI_FORCE is 1; this value determines if th = False R/W (0b0)
                                                       e VDD_SPI regulator is powered on
    VDD_SPI_TIEH (BLOCK0)                              If VDD_SPI_FORCE is 1; determines VDD_SPI voltage
       = VDD_SPI connects to 1.8 V LDO R/W (0b0)
    VDD_SPI_FORCE (BLOCK0)                             Set this bit to use XPD_VDD_PSI_REG and VDD_SPI_TI = False R/W (0b0)
                                                       EH to configure VDD_SPI LDO

    Wdt fuses:
    WDT_DELAY_SEL (BLOCK0)                             RTC watchdog timeout threshold; in unit of slow cl = 40000 R/W (0b00)
                                                       ock cycle

    Flash voltage (VDD_SPI) determined by GPIO45 on reset (GPIO45=High: VDD_SPI pin is powered from internal 1.8V LDO
    GPIO45=Low or NC: VDD_SPI pin is powered directly from VDD3P3_RTC_IO via resistor Rspi. Typically this voltage is 3.3 V).

To get a dump for all eFuse registers.

    idf.py efuse-dump

    Executing action: efuse-dump
    Running espefuse.py in directory <project-directory>
    Executing "espefuse.py dump --chip esp32s2"...
    espefuse.py v4.6-dev
    Connecting....
    BLOCK0          (                ) [0 ] read_regs: 00000000 00000000 00000000 00000000 00000000 00000000
    MAC_SPI_8M_0    (BLOCK1          ) [1 ] read_regs: 79b3b954 000058cf 00000000 10440000 00000000 00000000
    BLOCK_SYS_DATA  (BLOCK2          ) [2 ] read_regs: f1c60eea 8238f201 595b98e9 0200fe81 1c549f24 88491102 06461421 070c2083
    BLOCK_USR_DATA  (BLOCK3          ) [3 ] read_regs: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
    BLOCK_KEY0      (BLOCK4          ) [4 ] read_regs: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
    BLOCK_KEY1      (BLOCK5          ) [5 ] read_regs: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
    BLOCK_KEY2      (BLOCK6          ) [6 ] read_regs: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
    BLOCK_KEY3      (BLOCK7          ) [7 ] read_regs: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
    BLOCK_KEY4      (BLOCK8          ) [8 ] read_regs: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
    BLOCK_KEY5      (BLOCK9          ) [9 ] read_regs: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
    BLOCK_SYS_DATA2 (BLOCK10         ) [10] read_regs: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000

    BLOCK0          (                ) [0 ] err__regs: 00000000 00000000 00000000 00000000 00000000 00000000
    EFUSE_RD_RS_ERR0_REG        0x00000000
    EFUSE_RD_RS_ERR1_REG        0x00000000

    === Run "dump" command ===

## Application Examples

- system/efuse demonstrates how to use the eFuse API on ESP32-S2, showing read and write operations with fields from the common and custom eFuse tables, and explaining the use of virtual eFuses for debugging purposes.

## API Reference

### Header File

- components/efuse/esp32s2/include/esp_efuse_chip.h

- This header file can be included with:

  >     #include "esp_efuse_chip.h"

- This header file is a part of the API provided by the `efuse` component. To declare that your component depends on `efuse`, add the following to your CMakeLists.txt:

  >     REQUIRES efuse

  > or

  >     PRIV_REQUIRES efuse

### Enumerations

enum esp_efuse_block_t

  Type of eFuse blocks ESP32S2.

  Values:

  enumerator EFUSE_BLK0

    Number of eFuse BLOCK0. REPEAT_DATA

  enumerator EFUSE_BLK1

    Number of eFuse BLOCK1. MAC_SPI_8M_SYS

  enumerator EFUSE_BLK2

    Number of eFuse BLOCK2. SYS_DATA_PART1

  enumerator EFUSE_BLK_SYS_DATA_PART1

    Number of eFuse BLOCK2. SYS_DATA_PART1

  enumerator EFUSE_BLK3

    Number of eFuse BLOCK3. USER_DATA

  enumerator EFUSE_BLK_USER_DATA

    Number of eFuse BLOCK3. USER_DATA

  enumerator EFUSE_BLK4

    Number of eFuse BLOCK4. KEY0

  enumerator EFUSE_BLK_KEY0

    Number of eFuse BLOCK4. KEY0

  enumerator EFUSE_BLK5

    Number of eFuse BLOCK5. KEY1

  enumerator EFUSE_BLK_KEY1

    Number of eFuse BLOCK5. KEY1

  enumerator EFUSE_BLK6

    Number of eFuse BLOCK6. KEY2

  enumerator EFUSE_BLK_KEY2

    Number of eFuse BLOCK6. KEY2

  enumerator EFUSE_BLK7

    Number of eFuse BLOCK7. KEY3

  enumerator EFUSE_BLK_KEY3

    Number of eFuse BLOCK7. KEY3

  enumerator EFUSE_BLK8

    Number of eFuse BLOCK8. KEY4

  enumerator EFUSE_BLK_KEY4

    Number of eFuse BLOCK8. KEY4

  enumerator EFUSE_BLK9

    Number of eFuse BLOCK9. KEY5

  enumerator EFUSE_BLK_KEY5

    Number of eFuse BLOCK9. KEY5

  enumerator EFUSE_BLK_KEY_MAX
  enumerator EFUSE_BLK10

    Number of eFuse BLOCK10. SYS_DATA_PART2

  enumerator EFUSE_BLK_SYS_DATA_PART2

    Number of eFuse BLOCK10. SYS_DATA_PART2

  enumerator EFUSE_BLK_MAX

enum esp_efuse_coding_scheme_t

  Type of coding scheme.

  Values:

  enumerator EFUSE_CODING_SCHEME_NONE

    None

  enumerator EFUSE_CODING_SCHEME_RS

    Reed-Solomon coding

enum esp_efuse_purpose_t

  Type of key purpose.

  Values:

  enumerator ESP_EFUSE_KEY_PURPOSE_USER

    User purposes (software-only use)

  enumerator ESP_EFUSE_KEY_PURPOSE_RESERVED

    Reserved

  enumerator ESP_EFUSE_KEY_PURPOSE_XTS_AES_256_KEY_1

    XTS_AES_256_KEY_1 (flash/PSRAM encryption)

  enumerator ESP_EFUSE_KEY_PURPOSE_XTS_AES_256_KEY_2

    XTS_AES_256_KEY_2 (flash/PSRAM encryption)

  enumerator ESP_EFUSE_KEY_PURPOSE_XTS_AES_128_KEY

    XTS_AES_128_KEY (flash/PSRAM encryption)

  enumerator ESP_EFUSE_KEY_PURPOSE_HMAC_DOWN_ALL

    HMAC Downstream mode

  enumerator ESP_EFUSE_KEY_PURPOSE_HMAC_DOWN_JTAG

    JTAG soft enable key (uses HMAC Downstream mode)

  enumerator ESP_EFUSE_KEY_PURPOSE_HMAC_DOWN_DIGITAL_SIGNATURE

    Digital Signature peripheral key (uses HMAC Downstream mode)

  enumerator ESP_EFUSE_KEY_PURPOSE_HMAC_UP

    HMAC Upstream mode

  enumerator ESP_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST0

    SECURE_BOOT_DIGEST0 (Secure Boot key digest)

  enumerator ESP_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST1

    SECURE_BOOT_DIGEST1 (Secure Boot key digest)

  enumerator ESP_EFUSE_KEY_PURPOSE_SECURE_BOOT_DIGEST2

    SECURE_BOOT_DIGEST2 (Secure Boot key digest)

  enumerator ESP_EFUSE_KEY_PURPOSE_MAX

    MAX PURPOSE

### Header File

- components/efuse/include/esp_efuse.h

- This header file can be included with:

  >     #include "esp_efuse.h"

- This header file is a part of the API provided by the `efuse` component. To declare that your component depends on `efuse`, add the following to your CMakeLists.txt:

  >     REQUIRES efuse

  > or

  >     PRIV_REQUIRES efuse

### Functions

esp_err_t esp_efuse_read_field_blob(const esp_efuse_desc_t *field[], void *dst, size_t dst_size_bits)

  Reads bits from EFUSE field and writes it into an array.

  The number of read bits will be limited to the minimum value from the description of the bits in "field" structure or "dst_size_bits" required size. Use "esp_efuse_get_field_size()" function to determine the length of the field.

  Note

  Please note that reading in the batch mode does not show uncommitted changes.

  Parameters:

    - field -- [in] A pointer to the structure describing the fields of efuse.

    - dst -- [out] A pointer to array that will contain the result of reading.

    - dst_size_bits -- [in] The number of bits required to read. If the requested number of bits is greater than the field, the number will be limited to the field size.

  Returns:

    - ESP_OK: The operation was successfully completed.

    - ESP_ERR_INVALID_ARG: Error in the passed arguments.

bool esp_efuse_read_field_bit(const esp_efuse_desc_t *field[])

  Read a single bit eFuse field as a boolean value.

  Note

  The value must exist and must be a single bit wide. If there is any possibility of an error in the provided arguments, call esp_efuse_read_field_blob() and check the returned value instead.

  Note

  If assertions are enabled and the parameter is invalid, execution will abort

  Note

  Please note that reading in the batch mode does not show uncommitted changes.

  Parameters:

    field -- [in] A pointer to the structure describing the fields of efuse.

  Returns:

    - true: The field parameter is valid and the bit is set.

    - false: The bit is not set, or the parameter is invalid and assertions are disabled.

esp_err_t esp_efuse_read_field_cnt(const esp_efuse_desc_t *field[], size_t *out_cnt)

  Reads bits from EFUSE field and returns number of bits programmed as "1".

  If the bits are set not sequentially, they will still be counted.

  Note

  Please note that reading in the batch mode does not show uncommitted changes.

  Parameters:

    - field -- [in] A pointer to the structure describing the fields of efuse.

    - out_cnt -- [out] A pointer that will contain the number of programmed as "1" bits.

  Returns:

    - ESP_OK: The operation was successfully completed.

    - ESP_ERR_INVALID_ARG: Error in the passed arguments.

esp_err_t esp_efuse_write_field_blob(const esp_efuse_desc_t *field[], const void *src, size_t src_size_bits)

  Writes array to EFUSE field.

  The number of write bits will be limited to the minimum value from the description of the bits in "field" structure or "src_size_bits" required size. Use "esp_efuse_get_field_size()" function to determine the length of the field. After the function is completed, the writing registers are cleared.

  Parameters:

    - field -- [in] A pointer to the structure describing the fields of efuse.

    - src -- [in] A pointer to array that contains the data for writing.

    - src_size_bits -- [in] The number of bits required to write.

  Returns:

    - ESP_OK: The operation was successfully completed.

    - ESP_ERR_INVALID_ARG: Error in the passed arguments.

    - ESP_ERR_EFUSE_REPEATED_PROG: Error repeated programming of programmed bits is strictly forbidden.

    - ESP_ERR_CODING: Error range of data does not match the coding scheme.

esp_err_t esp_efuse_write_field_cnt(const esp_efuse_desc_t *field[], size_t cnt)

  Writes a required count of bits as "1" to EFUSE field.

  If there are no free bits in the field to set the required number of bits to "1", ESP_ERR_EFUSE_CNT_IS_FULL error is returned, the field will not be partially recorded. After the function is completed, the writing registers are cleared.

  Parameters:

    - field -- [in] A pointer to the structure describing the fields of efuse.

    - cnt -- [in] Required number of programmed as "1" bits.

  Returns:

    - ESP_OK: The operation was successfully completed.

    - ESP_ERR_INVALID_ARG: Error in the passed arguments.

    - ESP_ERR_EFUSE_CNT_IS_FULL: Not all requested cnt bits is set.

esp_err_t esp_efuse_write_field_bit(const esp_efuse_desc_t *field[])

  Write a single bit eFuse field to 1.

  For use with eFuse fields that are a single bit. This function will write the bit to value 1 if it is not already set, or does nothing if the bit is already set.

  This is equivalent to calling esp_efuse_write_field_cnt() with the cnt parameter equal to 1, except that it will return ESP_OK if the field is already set to 1.

  Parameters:

    field -- [in] Pointer to the structure describing the efuse field.

  Returns:

    - ESP_OK: The operation was successfully completed, or the bit was already set to value 1.

    - ESP_ERR_INVALID_ARG: Error in the passed arguments, including if the efuse field is not 1 bit wide.

esp_err_t esp_efuse_set_write_protect(esp_efuse_block_t blk)

  Sets a write protection for the whole block.

  After that, it is impossible to write to this block. The write protection does not apply to block 0.

  Parameters:

    blk -- [in] Block number of eFuse. (EFUSE_BLK1, EFUSE_BLK2 and EFUSE_BLK3)

  Returns:

    - ESP_OK: The operation was successfully completed.

    - ESP_ERR_INVALID_ARG: Error in the passed arguments.

    - ESP_ERR_EFUSE_CNT_IS_FULL: Not all requested cnt bits is set.

    - ESP_ERR_NOT_SUPPORTED: The block does not support this command.

esp_err_t esp_efuse_set_read_protect(esp_efuse_block_t blk)

  Sets a read protection for the whole block.

  After that, it is impossible to read from this block. The read protection does not apply to block 0.

  Parameters:

    blk -- [in] Block number of eFuse. (EFUSE_BLK1, EFUSE_BLK2 and EFUSE_BLK3)

  Returns:

    - ESP_OK: The operation was successfully completed.

    - ESP_ERR_INVALID_ARG: Error in the passed arguments.

    - ESP_ERR_EFUSE_CNT_IS_FULL: Not all requested cnt bits is set.

    - ESP_ERR_NOT_SUPPORTED: The block does not support this command.

int esp_efuse_get_field_size(const esp_efuse_desc_t *field[])

  Returns the number of bits used by field.

  Parameters:

    field -- [in] A pointer to the structure describing the fields of efuse.

  Returns:

    Returns the number of bits used by field.

uint32_t esp_efuse_read_reg(esp_efuse_block_t blk, unsigned int num_reg)

  Returns value of efuse register.

  This is a thread-safe implementation. Example: EFUSE_BLK2_RDATA3_REG where (blk=2, num_reg=3)

  Note

  Please note that reading in the batch mode does not show uncommitted changes.

  Parameters:

    - blk -- [in] Block number of eFuse.

    - num_reg -- [in] The register number in the block.

  Returns:

    Value of register

esp_err_t esp_efuse_write_reg(esp_efuse_block_t blk, unsigned int num_reg, uint32_t val)

  Write value to efuse register.

  Apply a coding scheme if necessary. This is a thread-safe implementation. Example: EFUSE_BLK3_WDATA0_REG where (blk=3, num_reg=0)

  Parameters:

    - blk -- [in] Block number of eFuse.

    - num_reg -- [in] The register number in the block.

    - val -- [in] Value to write.

  Returns:

    - ESP_OK: The operation was successfully completed.

    - ESP_ERR_EFUSE_REPEATED_PROG: Error repeated programming of programmed bits is strictly forbidden.

esp_efuse_coding_scheme_t esp_efuse_get_coding_scheme(esp_efuse_block_t blk)

  Return efuse coding scheme for blocks.

  Note

  The coding scheme is applicable only to 1, 2 and 3 blocks. For 0 block, the coding scheme is always `NONE`.

  Parameters:

    blk -- [in] Block number of eFuse.

  Returns:

    Return efuse coding scheme for blocks

esp_err_t esp_efuse_read_block(esp_efuse_block_t blk, void *dst_key, size_t offset_in_bits, size_t size_bits)

  Read key to efuse block starting at the offset and the required size.

  Note

  Please note that reading in the batch mode does not show uncommitted changes.

  Parameters:

    - blk -- [in] Block number of eFuse.

    - dst_key -- [in] A pointer to array that will contain the result of reading.

    - offset_in_bits -- [in] Start bit in block.

    - size_bits -- [in] The number of bits required to read.

  Returns:

    - ESP_OK: The operation was successfully completed.

    - ESP_ERR_INVALID_ARG: Error in the passed arguments.

    - ESP_ERR_CODING: Error range of data does not match the coding scheme.

esp_err_t esp_efuse_write_block(esp_efuse_block_t blk, const void *src_key, size_t offset_in_bits, size_t size_bits)

  Write key to efuse block starting at the offset and the required size.

  Parameters:

    - blk -- [in] Block number of eFuse.

    - src_key -- [in] A pointer to array that contains the key for writing.

    - offset_in_bits -- [in] Start bit in block.

    - size_bits -- [in] The number of bits required to write.

  Returns:

    - ESP_OK: The operation was successfully completed.

    - ESP_ERR_INVALID_ARG: Error in the passed arguments.

    - ESP_ERR_CODING: Error range of data does not match the coding scheme.

    - ESP_ERR_EFUSE_REPEATED_PROG: Error repeated programming of programmed bits

uint32_t esp_efuse_get_pkg_ver(void)

  Returns chip package from efuse.

  Returns:

    chip package

void esp_efuse_reset(void)

  Reset efuse write registers.

  Efuse write registers are written to zero, to negate any changes that have been staged here.

  Note

  This function is not threadsafe, if calling code updates efuse values from multiple tasks then this is caller's responsibility to serialise.

esp_err_t esp_efuse_disable_rom_download_mode(void)

  Disable ROM Download Mode via eFuse.

  Permanently disables the ROM Download Mode feature. Once disabled, if the SoC is booted with strapping pins set for ROM Download Mode then an error is printed instead.

  Note

  Not all SoCs support this option. An error will be returned if called on an ESP32 with a silicon revision lower than 3, as these revisions do not support this option.

  Note

  If ROM Download Mode is already disabled, this function does nothing and returns success.

  Returns:

    - ESP_OK If the eFuse was successfully burned, or had already been burned.

    - ESP_ERR_NOT_SUPPORTED (ESP32 only) This SoC is not capable of disabling UART download mode

    - ESP_ERR_INVALID_STATE (ESP32 only) This eFuse is write protected and cannot be written

esp_err_t esp_efuse_set_rom_log_scheme(esp_efuse_rom_log_scheme_t log_scheme)

  Set boot ROM log scheme via eFuse.

  Note

  By default, the boot ROM will always print to console. This API can be called to set the log scheme only once per chip, once the value is changed from the default it can't be changed again.

  Parameters:

    log_scheme -- Supported ROM log scheme

  Returns:

    - ESP_OK If the eFuse was successfully burned, or had already been burned.

    - ESP_ERR_NOT_SUPPORTED (ESP32 only) This SoC is not capable of setting ROM log scheme

    - ESP_ERR_INVALID_STATE This eFuse is write protected or has been burned already

esp_err_t esp_efuse_enable_rom_secure_download_mode(void)

  Switch ROM Download Mode to Secure Download mode via eFuse.

  Permanently enables Secure Download mode. This mode limits the use of ROM Download Mode functions to simple flash read, write and erase operations, plus a command to return a summary of currently enabled security features.

  Note

  If Secure Download mode is already enabled, this function does nothing and returns success.

  Note

  Disabling the ROM Download Mode also disables Secure Download Mode.

  Returns:

    - ESP_OK If the eFuse was successfully burned, or had already been burned.

    - ESP_ERR_INVALID_STATE ROM Download Mode has been disabled via eFuse, so Secure Download mode is unavailable.

uint32_t esp_efuse_read_secure_version(void)

  Return secure_version from efuse field.

  Returns:

    Secure version from efuse field

bool esp_efuse_check_secure_version(uint32_t secure_version)

  Check secure_version from app and secure_version and from efuse field.

  Parameters:

    secure_version -- Secure version from app.

  Returns:

    - True: If version of app is equal or more then secure_version from efuse.

esp_err_t esp_efuse_update_secure_version(uint32_t secure_version)

  Write efuse field by secure_version value.

  Update the secure_version value is available if the coding scheme is None. Note: Do not use this function in your applications. This function is called as part of the other API.

  Parameters:

    secure_version -- [in] Secure version from app.

  Returns:

    - ESP_OK: Successful.

    - ESP_FAIL: secure version of app cannot be set to efuse field.

    - ESP_ERR_NOT_SUPPORTED: Anti rollback is not supported with the 3/4 and Repeat coding scheme.

esp_err_t esp_efuse_batch_write_begin(void)

  Set the batch mode of writing fields.

  This mode allows you to write the fields in the batch mode when need to burn several efuses at one time. To enable batch mode call begin() then perform as usually the necessary operations read and write and at the end call commit() to actually burn all written efuses. The batch mode can be used nested. The commit will be done by the last commit() function. The number of begin() functions should be equal to the number of commit() functions.

  Note: If batch mode is enabled by the first task, at this time the second task cannot write/read efuses. The second task will wait for the first task to complete the batch operation.

      // Example of using the batch writing mode.

      // set the batch writing mode
      esp_efuse_batch_write_begin();

      // use any writing functions as usual
      esp_efuse_write_field_blob(ESP_EFUSE_...);
      esp_efuse_write_field_cnt(ESP_EFUSE_...);
      esp_efuse_set_write_protect(EFUSE_BLKx);
      esp_efuse_write_reg(EFUSE_BLKx, ...);
      esp_efuse_write_block(EFUSE_BLKx, ...);
      esp_efuse_write(ESP_EFUSE_1, 3);  // ESP_EFUSE_1 == 1, here we write a new value = 3. The changes will be burn by the commit() function.
      esp_efuse_read_...(ESP_EFUSE_1);  // this function returns ESP_EFUSE_1 == 1 because uncommitted changes are not readable, it will be available only after commit.
      ...

      // esp_efuse_batch_write APIs can be called recursively.
      esp_efuse_batch_write_begin();
      esp_efuse_set_write_protect(EFUSE_BLKx);
      esp_efuse_batch_write_commit(); // the burn will be skipped here, it will be done in the last commit().

      ...

      // Write all of these fields to the efuse registers
      esp_efuse_batch_write_commit();
      esp_efuse_read_...(ESP_EFUSE_1);  // this function returns ESP_EFUSE_1 == 3.

  Note

  Please note that reading in the batch mode does not show uncommitted changes.

  Returns:

    - ESP_OK: Successful.

esp_err_t esp_efuse_batch_write_cancel(void)

  Reset the batch mode of writing fields.

  It will reset the batch writing mode and any written changes.

  Returns:

    - ESP_OK: Successful.

    - ESP_ERR_INVALID_STATE: The batch mode was not set.

esp_err_t esp_efuse_batch_write_commit(void)

  Writes all prepared data for the batch mode.

  Must be called to ensure changes are written to the efuse registers. After this the batch writing mode will be reset.

  Returns:

    - ESP_OK: Successful.

    - ESP_ERR_INVALID_STATE: The deferred writing mode was not set.

bool esp_efuse_block_is_empty(esp_efuse_block_t block)

  Checks that the given block is empty.

  Returns:

    - True: The block is empty.

    - False: The block is not empty or was an error.

bool esp_efuse_get_key_dis_read(esp_efuse_block_t block)

  Returns a read protection for the key block.

  Parameters:

    block -- [in] A key block in the range EFUSE_BLK_KEY0..EFUSE_BLK_KEY_MAX

  Returns:

    True: The key block is read protected False: The key block is readable.

esp_err_t esp_efuse_set_key_dis_read(esp_efuse_block_t block)

  Sets a read protection for the key block.

  Parameters:

    block -- [in] A key block in the range EFUSE_BLK_KEY0..EFUSE_BLK_KEY_MAX

  Returns:

    - ESP_OK: Successful.

    - ESP_ERR_INVALID_ARG: Error in the passed arguments.

    - ESP_ERR_EFUSE_REPEATED_PROG: Error repeated programming of programmed bits is strictly forbidden.

    - ESP_ERR_CODING: Error range of data does not match the coding scheme.

bool esp_efuse_get_key_dis_write(esp_efuse_block_t block)

  Returns a write protection for the key block.

  Parameters:

    block -- [in] A key block in the range EFUSE_BLK_KEY0..EFUSE_BLK_KEY_MAX

  Returns:

    True: The key block is write protected False: The key block is writeable.

esp_err_t esp_efuse_set_key_dis_write(esp_efuse_block_t block)

  Sets a write protection for the key block.

  Parameters:

    block -- [in] A key block in the range EFUSE_BLK_KEY0..EFUSE_BLK_KEY_MAX

  Returns:

    - ESP_OK: Successful.

    - ESP_ERR_INVALID_ARG: Error in the passed arguments.

    - ESP_ERR_EFUSE_REPEATED_PROG: Error repeated programming of programmed bits is strictly forbidden.

    - ESP_ERR_CODING: Error range of data does not match the coding scheme.

bool esp_efuse_key_block_unused(esp_efuse_block_t block)

  Returns true if the key block is unused, false otherwise.

  An unused key block is all zero content, not read or write protected, and has purpose 0 (ESP_EFUSE_KEY_PURPOSE_USER)

  Parameters:

    block -- key block to check.

  Returns:

    - True if key block is unused,

    - False if key block is used or the specified block index is not a key block.

bool esp_efuse_find_purpose(esp_efuse_purpose_t purpose, esp_efuse_block_t *block)

  Find a key block with the particular purpose set.

  Parameters:

    - purpose -- [in] Purpose to search for.

    - block -- [out] Pointer in the range EFUSE_BLK_KEY0..EFUSE_BLK_KEY_MAX which will be set to the key block if found. Can be NULL, if only need to test the key block exists.

  Returns:

    - True: If found,

    - False: If not found (value at block pointer is unchanged).

bool esp_efuse_get_keypurpose_dis_write(esp_efuse_block_t block)

  Returns a write protection of the key purpose field for an efuse key block.

  Note

  For ESP32: no keypurpose, it returns always True.

  Parameters:

    block -- [in] A key block in the range EFUSE_BLK_KEY0..EFUSE_BLK_KEY_MAX

  Returns:

    True: The key purpose is write protected. False: The key purpose is writeable.

esp_efuse_purpose_t esp_efuse_get_key_purpose(esp_efuse_block_t block)

  Returns the current purpose set for an efuse key block.

  Parameters:

    block -- [in] A key block in the range EFUSE_BLK_KEY0..EFUSE_BLK_KEY_MAX

  Returns:

    - Value: If Successful, it returns the value of the purpose related to the given key block.

    - ESP_EFUSE_KEY_PURPOSE_MAX: Otherwise.

const esp_efuse_desc_t **esp_efuse_get_purpose_field(esp_efuse_block_t block)

  Returns a pointer to a key purpose for an efuse key block.

  To get the value of this field use esp_efuse_read_field_blob() or esp_efuse_get_key_purpose().

  Parameters:

    block -- [in] A key block in the range EFUSE_BLK_KEY0..EFUSE_BLK_KEY_MAX

  Returns:

    Pointer: If Successful returns a pointer to the corresponding efuse field otherwise NULL.

const esp_efuse_desc_t **esp_efuse_get_key(esp_efuse_block_t block)

  Returns a pointer to a key block.

  Parameters:

    block -- [in] A key block in the range EFUSE_BLK_KEY0..EFUSE_BLK_KEY_MAX

  Returns:

    Pointer: If Successful returns a pointer to the corresponding efuse field otherwise NULL.

esp_err_t esp_efuse_set_key_purpose(esp_efuse_block_t block, esp_efuse_purpose_t purpose)

  Sets a key purpose for an efuse key block.

  Parameters:

    - block -- [in] A key block in the range EFUSE_BLK_KEY0..EFUSE_BLK_KEY_MAX

    - purpose -- [in] Key purpose.

  Returns:

    - ESP_OK: Successful.

    - ESP_ERR_INVALID_ARG: Error in the passed arguments.

    - ESP_ERR_EFUSE_REPEATED_PROG: Error repeated programming of programmed bits is strictly forbidden.

    - ESP_ERR_CODING: Error range of data does not match the coding scheme.

esp_err_t esp_efuse_set_keypurpose_dis_write(esp_efuse_block_t block)

  Sets a write protection of the key purpose field for an efuse key block.

  Parameters:

    block -- [in] A key block in the range EFUSE_BLK_KEY0..EFUSE_BLK_KEY_MAX

  Returns:

    - ESP_OK: Successful.

    - ESP_ERR_INVALID_ARG: Error in the passed arguments.

    - ESP_ERR_EFUSE_REPEATED_PROG: Error repeated programming of programmed bits is strictly forbidden.

    - ESP_ERR_CODING: Error range of data does not match the coding scheme.

esp_efuse_block_t esp_efuse_find_unused_key_block(void)

  Search for an unused key block and return the first one found.

  See esp_efuse_key_block_unused for a description of an unused key block.

  Returns:

    First unused key block, or EFUSE_BLK_KEY_MAX if no unused key block is found.

unsigned esp_efuse_count_unused_key_blocks(void)

  Return the number of unused efuse key blocks in the range EFUSE_BLK_KEY0..EFUSE_BLK_KEY_MAX.

bool esp_efuse_get_digest_revoke(unsigned num_digest)

  Returns the status of the Secure Boot public key digest revocation bit.

  Parameters:

    num_digest -- [in] The number of digest in range 0..2

  Returns:

    - True: If key digest is revoked,

    - False; If key digest is not revoked.

esp_err_t esp_efuse_set_digest_revoke(unsigned num_digest)

  Sets the Secure Boot public key digest revocation bit.

  Parameters:

    num_digest -- [in] The number of digest in range 0..2

  Returns:

    - ESP_OK: Successful.

    - ESP_ERR_INVALID_ARG: Error in the passed arguments.

    - ESP_ERR_EFUSE_REPEATED_PROG: Error repeated programming of programmed bits is strictly forbidden.

    - ESP_ERR_CODING: Error range of data does not match the coding scheme.

bool esp_efuse_get_write_protect_of_digest_revoke(unsigned num_digest)

  Returns a write protection of the Secure Boot public key digest revocation bit.

  Parameters:

    num_digest -- [in] The number of digest in range 0..2

  Returns:

    True: The revocation bit is write protected. False: The revocation bit is writeable.

esp_err_t esp_efuse_set_write_protect_of_digest_revoke(unsigned num_digest)

  Sets a write protection of the Secure Boot public key digest revocation bit.

  Parameters:

    num_digest -- [in] The number of digest in range 0..2

  Returns:

    - ESP_OK: Successful.

    - ESP_ERR_INVALID_ARG: Error in the passed arguments.

    - ESP_ERR_EFUSE_REPEATED_PROG: Error repeated programming of programmed bits is strictly forbidden.

    - ESP_ERR_CODING: Error range of data does not match the coding scheme.

esp_err_t esp_efuse_write_key(esp_efuse_block_t block, esp_efuse_purpose_t purpose, const void *key, size_t key_size_bytes)

  Program a block of key data to an efuse block.

  The burn of a key, protection bits, and a purpose happens in batch mode.

  Note

  This API also enables the read protection efuse bit for certain key blocks like XTS-AES, HMAC, ECDSA etc. This ensures that the key is only accessible to hardware peripheral.

  Note

  For SoC's with capability `SOC_EFUSE_ECDSA_USE_HARDWARE_K` (e.g., ESP32-H2), this API writes an additional efuse bit for ECDSA key purpose to enforce hardware TRNG generated k mode in the peripheral.

  Parameters:

    - block -- [in] Block to read purpose for. Must be in range EFUSE_BLK_KEY0 to EFUSE_BLK_KEY_MAX. Key block must be unused (esp_efuse_key_block_unused).

    - purpose -- [in] Purpose to set for this key. Purpose must be already unset.

    - key -- [in] Pointer to data to write.

    - key_size_bytes -- [in] Bytes length of data to write.

  Returns:

    - ESP_OK: Successful.

    - ESP_ERR_INVALID_ARG: Error in the passed arguments.

    - ESP_ERR_INVALID_STATE: Error in efuses state, unused block not found.

    - ESP_ERR_EFUSE_REPEATED_PROG: Error repeated programming of programmed bits is strictly forbidden.

    - ESP_ERR_CODING: Error range of data does not match the coding scheme.

esp_err_t esp_efuse_write_keys(const esp_efuse_purpose_t purposes[], uint8_t keys[][32], unsigned number_of_keys)

  Program keys to unused efuse blocks.

  The burn of keys, protection bits, and purposes happens in batch mode.

  Note

  This API also enables the read protection efuse bit for certain key blocks like XTS-AES, HMAC, ECDSA etc. This ensures that the key is only accessible to hardware peripheral.

  Note

  For SoC's with capability `SOC_EFUSE_ECDSA_USE_HARDWARE_K` (e.g., ESP32-H2), this API writes an additional efuse bit for ECDSA key purpose to enforce hardware TRNG generated k mode in the peripheral.

  Parameters:

    - purposes -- [in] Array of purposes (purpose[number_of_keys]).

    - keys -- [in] Array of keys (uint8_t keys[number_of_keys][32]). Each key is 32 bytes long.

    - number_of_keys -- [in] The number of keys to write (up to 6 keys).

  Returns:

    - ESP_OK: Successful.

    - ESP_ERR_INVALID_ARG: Error in the passed arguments.

    - ESP_ERR_INVALID_STATE: Error in efuses state, unused block not found.

    - ESP_ERR_NOT_ENOUGH_UNUSED_KEY_BLOCKS: Error not enough unused key blocks available

    - ESP_ERR_EFUSE_REPEATED_PROG: Error repeated programming of programmed bits is strictly forbidden.

    - ESP_ERR_CODING: Error range of data does not match the coding scheme.

esp_err_t esp_secure_boot_read_key_digests(esp_secure_boot_key_digests_t *trusted_key_digests)

  Read key digests from efuse. Any revoked/missing digests will be marked as NULL.

  Parameters:

    trusted_key_digests -- [out] Trusted keys digests, stored in this parameter after successfully completing this function. The number of digests depends on the SOC's capabilities.

  Returns:

    - ESP_OK: Successful.

    - ESP_FAIL: If trusted_keys is NULL or there is no valid digest.

esp_err_t esp_efuse_check_errors(void)

  Checks eFuse errors in BLOCK0.

  It does a BLOCK0 check if eFuse EFUSE_ERR_RST_ENABLE is set. If BLOCK0 has an error, it prints the error and returns ESP_FAIL, which should be treated as esp_restart.

  Note

  Refers to ESP32-C3 only.

  Returns:

    - ESP_OK: No errors in BLOCK0.

    - ESP_FAIL: Error in BLOCK0 requiring reboot.

esp_err_t esp_efuse_destroy_block(esp_efuse_block_t block)

  Destroys the data in the given efuse block, if possible.

  Data destruction occurs through the following steps: 1) Destroy data in the block:

  - If write protection is inactive for the block, then unset bits are burned.

  - If write protection is active, the block remains unaltered. 2) Set read protection for the block if possible (check write-protection for RD_DIS). In this case, data becomes inaccessible, and the software reads it as all zeros. If write protection is enabled and read protection can not be set, data in the block remains readable (returns an error).

  Do not use the batch mode with this function as it does the burning itself!

  Parameters:

    block -- [in] A key block in the range EFUSE_BLK_KEY0..EFUSE_BLK_KEY_MAX

  Returns:

    - ESP_OK: Successful.

    - ESP_FAIL: Data remained readable because the block is write-protected and read protection can not be set.

### Structures

struct esp_efuse_desc_t

  Type definition for an eFuse field.

  Public Members

  esp_efuse_block_t efuse_block

    Block of eFuse

  uint8_t bit_start

    Start bit [0..255]

  uint16_t bit_count

    Length of bit field [1..-]

struct esp_secure_boot_key_digests_t

  Pointers to the trusted key digests.

  The number of digests depends on the SOC's capabilities.

  Public Members

  const void *key_digests[3]

    Pointers to the key digests

### Macros

ESP_ERR_EFUSE

  Base error code for efuse api.

ESP_OK_EFUSE_CNT

  OK the required number of bits is set.

ESP_ERR_EFUSE_CNT_IS_FULL

  Error field is full.

ESP_ERR_EFUSE_REPEATED_PROG

  Error repeated programming of programmed bits is strictly forbidden.

ESP_ERR_CODING

  Error while a encoding operation.

ESP_ERR_NOT_ENOUGH_UNUSED_KEY_BLOCKS

  Error not enough unused key blocks available

ESP_ERR_DAMAGED_READING

  Error. Burn or reset was done during a reading operation leads to damage read data. This error is internal to the efuse component and not returned by any public API.

### Enumerations

enum esp_efuse_rom_log_scheme_t

  Type definition for ROM log scheme.

  Values:

  enumerator ESP_EFUSE_ROM_LOG_ALWAYS_ON

    Always enable ROM logging

  enumerator ESP_EFUSE_ROM_LOG_ON_GPIO_LOW

    ROM logging is enabled when specific GPIO level is low during start up

  enumerator ESP_EFUSE_ROM_LOG_ON_GPIO_HIGH

    ROM logging is enabled when specific GPIO level is high during start up

  enumerator ESP_EFUSE_ROM_LOG_ALWAYS_OFF

    Disable ROM logging permanently

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