Warning

This document is not updated for ESP32C5 yet, so some of the content may not be correct.

This warning was automatically inserted due to the source file being in the add_warnings_pages list.

# eFuse Manager

## Introduction

The eFuse Manager library is designed to structure access to eFuse bits and make using these easy. This library operates eFuse bits by a structure name which is assigned in eFuse table. This sections introduces some concepts used by eFuse Manager.

## Hardware Description

The ESP32-C5 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. Some of system parameters are using these eFuse bits directly by hardware modules and have special place (for example EFUSE_BLK0).

For more details, see ESP32-C5 Technical Reference Manual > eFuse Controller (eFuse) [PDF]. Some eFuse bits are available for user applications.

ESP32-C5 has 11 eFuse blocks each of the size of 256 bits (not all bits are available):

- EFUSE_BLK0 is used entirely for system purposes;

- EFUSE_BLK1 is used entirely for system purposes;

- EFUSE_BLK2 is used entirely for system purposes;

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

- EFUSE_BLK4 (also named EFUSE_BLK_KEY0) can be used as key (for secure_boot or flash_encryption) or for user purposes;

- EFUSE_BLK5 (also named EFUSE_BLK_KEY1) can be used as key (for secure_boot or flash_encryption) or for user purposes;

- EFUSE_BLK6 (also named EFUSE_BLK_KEY2) can be used as key (for secure_boot or flash_encryption) or for user purposes;

- EFUSE_BLK7 (also named EFUSE_BLK_KEY3) can be used as key (for secure_boot or flash_encryption) or for user purposes;

- EFUSE_BLK8 (also named EFUSE_BLK_KEY4) can be used as key (for secure_boot or flash_encryption) or for user purposes;

- EFUSE_BLK9 (also named EFUSE_BLK_KEY5) can be used as key (for secure_boot or flash_encryption) or for user purposes;

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

Each block is divided into 8 32-bits registers.

## eFuse Manager Component

The component has API functions for reading and writing fields. Access to the fields is carried out through the structures that describe the location of the eFuse bits in the blocks. The component provides the ability to form fields of any length and from any number of individual bits. The description of the fields is made in a CSV file in a table form. To generate from a tabular form (CSV file) in the C-source uses the tool `efuse_table_gen.py`. The tool checks the CSV file for uniqueness of field names and bit intersection, in case of using a custom file from the user's project directory, the utility checks with the common CSV file.

CSV files:

- common (esp_efuse_table.csv) - contains eFuse fields which are used inside the ESP-IDF. C-source generation should be done manually when changing this file (run command `idf.py efuse-common-table`). Note that changes in this file can lead to incorrect operation.

- custom - (optional and can be enabled by CONFIG_EFUSE_CUSTOM_TABLE) contains eFuse fields that are used by the user in their application. C-source generation should be done manually when changing this file and running `idf.py efuse-custom-table`.

## Description CSV File

The CSV file contains a description of the eFuse fields. In the simple case, one field has one line of description. Table header:

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

Individual params in CSV file the following meanings:

field_name

> Name of field. The prefix ESP_EFUSE_ is added to the name, and this field name is available in the code. This name is used to access the fields. The name must be unique for all fields. If the line has an empty name, then this line is combined with the previous field. This allows you to set an arbitrary order of bits in the field, and expand the field as well (see `MAC_FACTORY` field in the common table). The field_name supports structured format using . to show that the field belongs to another field (see `WR_DIS` and `RD_DIS` in the common table).

efuse_block

> Block number. It determines where the eFuse bits are placed for this field. Available EFUSE_BLK0..EFUSE_BLK10.

bit_start

> Start bit number (0..255). The bit_start field can be omitted. In this case, it is set to bit_start + bit_count from the previous record, if it has the same efuse_block. Otherwise (if efuse_block is different, or this is the first entry), an error will be generated.

bit_count

> The number of bits to use in this field (1..-). This parameter cannot be omitted. This field also may be `MAX_BLK_LEN` in this case, the field length has the maximum block length.

comment

> This param is using for comment field, it also move to C-header file. The comment field can be omitted.

If a non-sequential bit order is required to describe a field, then the field description in the following lines should be continued without specifying a name, indicating that it belongs to one field. For example two fields `MAC_FACTORY` and `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 field is available in code as `ESP_EFUSE_MAC_FACTORY` and `ESP_EFUSE_MAC_FACTORY_CRC`.

## Structured eFuse Fields

    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

The structured eFuse field looks like `WR_DIS.RD_DIS` where the dot points that this field belongs to the parent field - `WR_DIS` and cannot be out of the parent's range.

It is possible to use some levels of structured fields as WR_DIS.FIELD_2.B1 and B2. These fields should not be crossed each other and should be in the range of two fields: `WR_DIS` and `WR_DIS.FIELD_2`.

It is possible to create aliases for fields with the same range, see `WR_DIS.FIELD_3` and `WR_DIS.FIELD_3.ALIAS`.

The ESP-IDF names for structured eFuse fields should be unique. The `efuse_table_gen` tool generates the final names where the dot is replaced by `_`. The names for using in ESP-IDF are ESP_EFUSE_WR_DIS, ESP_EFUSE_WR_DIS_RD_DIS, ESP_EFUSE_WR_DIS_FIELD_2_B1, etc.

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

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

Solution: Describe `SERIAL_NUMBER` to be included in `USER_DATA`. (`USER_DATA.SERIAL_NUMBER`).

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

Solution: Change `bit_start` for `FIELD.MAJOR_NUMBER` from 60 to 0, so `MAJOR_NUMBER` is in the `FIELD` range.

## `efuse_table_gen.py` Tool

The tool is designed to generate C-source files from CSV file and validate fields. First of all, the check is carried out on the uniqueness of the names and overlaps of the field bits. If an additional custom file is used, it will be checked with the existing common file (esp_efuse_table.csv). In case of errors, a message will be displayed and the string that caused the error. C-source files contain structures of type esp_efuse_desc_t.

To generate a common files, use the following command `idf.py efuse-common-table` or:

    cd $IDF_PATH/components/efuse/
    ./efuse_table_gen.py --idf_target esp32c5 esp32c5/esp_efuse_table.csv

After generation in the folder $IDF_PATH/components/efuse/esp32c5 create:

- esp_efuse_table.c file.

- In include folder esp_efuse_table.c file.

To generate a custom files, use the following command `idf.py efuse-custom-table` or:

    cd $IDF_PATH/components/efuse/
    ./efuse_table_gen.py --idf_target esp32c5 esp32c5/esp_efuse_table.csv PROJECT_PATH/main/esp_efuse_custom_table.csv

After generation in the folder PROJECT_PATH/main create:

- esp_efuse_custom_table.c file.

- In include folder esp_efuse_custom_table.c file.

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 Scheme

Coding schemes are used to protect against data corruption. ESP32-C5 supports two coding schemes:

- `None`. EFUSE_BLK0 is stored with four backups, meaning each bit is stored four times. This backup scheme is automatically applied by the hardware and is not visible to software. EFUSE_BLK0 can be written many times.

- `RS`. EFUSE_BLK1 - EFUSE_BLK10 use Reed-Solomon coding scheme that supports up to 5 bytes of automatic error correction. Software encodes the 32-byte EFUSE_BLKx using RS (44, 32) to generate a 12-byte check code, and then burn the EFUSE_BLKx and the check code 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 codes are generated across the entire 256-bit eFuse block, each block can only be written to one time.

To write some fields into one block, or different blocks in one time, you need to use `the batch writing mode`. Firstly set this mode through `esp_efuse_batch_write_begin()` function then write some fields as usual using the `esp_efuse_write_...` functions. At the end to burn them, call the `esp_efuse_batch_write_commit()` function. It burns prepared data to the eFuse blocks and disables the `batch recording mode`.

Note

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 encoding data. This encoding data will be overwritten with new encoding data and completely destroyed (however, the payload eFuses are not damaged). It can be related to: CUSTOM_MAC, SPI_PAD_CONFIG_HD, SPI_PAD_CONFIG_CS, etc. Please contact Espressif to order 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 key to eFuse block starting at the offset and the required size.

- `esp_efuse_write_block()` - writes key to eFuse block starting at the offset and the 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..EFUSE_BLK_KEY_MAX

## How to Add a New Field

1. Find a free bits for field. Show esp_efuse_table.csv file or run `idf.py show-efuse-table` or the next command:

    To be updated for C5

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

To add fields to an existing field, use the Structured efuse fields technique. For example, adding the fields: SERIAL_NUMBER, MODEL_NUMBER and HARDWARE REV to an existing `USER_DATA` field. Use `.` (dot) to show an attachment in a field.

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

2. Fill a line for field: field_name, efuse_block, bit_start, bit_count, comment.

3. Run a `show_efuse_table` command to check eFuse table. To generate source files run `efuse_common_table` or `efuse_custom_table` command.

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), it means that eFuse bits are read and written from LSB to MSB:

    $ espefuse.py 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` (get-started/hello_world/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`.

    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-summary`. This allows you to run the `idf.py efuse-summary` command to read the required eFuses (specified in the `efuse_names` list) at any time, not just at project build time.

## 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 app and unit tests. 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 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 the efuse partition. partition.csv: `"efuse_em, data, efuse, , 0x2000,"`. During startup, the eFuses are copied from flash or, in case if flash is empty, from real eFuse to RAM and then update flash. This option allows keeping eFuses after reboots (possible to test secure_boot and flash_encryption features with this option).

#### Flash Encryption Testing

Flash Encryption (FE) is a hardware feature that requires the physical burning of eFuses: key and FLASH_CRYPT_CNT. If FE is not actually enabled then enabling the CONFIG_EFUSE_VIRTUAL_KEEP_IN_FLASH option just gives testing possibilities and does not encrypt anything in the flash, even though the logs say encryption happens. The `bootloader_flash_write()` is adapted for this purpose. But if FE is already enabled on the chip and you run an application or bootloader created with the CONFIG_EFUSE_VIRTUAL_KEEP_IN_FLASH option then the flash encryption/decryption operations will work properly (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-C5 eFuse bits - espefuse.py.

    To be updated for C5

### Header File

- components/efuse/esp32c5/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 ESP32C5.

  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_ECDSA_KEY

    ECDSA private key (Expected in little endian order)

  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.

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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