eFuse Manager

Introduction

eFuse (Electronic Fuses) are microscopic one-time programmable fuses that can be "burned" (i.e., programmed) to store data into the ESP32-C2. 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-C2) 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-C2 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-C2 Technical Reference Manual > eFuse Controller (eFuse) [PDF].

ESP32-C2 has 4 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_KEY0) 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.

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_BLK3), 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_BLK3.
- 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-C2, 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 esp32c2 esp32c2/esp_efuse_table.csv

The following C source/header files will be generated by the tool in $IDF_PATH/components/efuse/esp32c2:

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 esp32c2 esp32c2/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-C2 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_BLK3

`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_BLK3. 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:

Enable batch writing mode by calling esp_efuse_batch_write_begin()
Write to the eFuse fields as usual using various esp_efuse_write_... functions.
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().

How to Add a New Field

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 esp32c2/esp_efuse_table.csv --info

Parsing efuse CSV input file $IDF_PATH/components/efuse/esp32c2/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
     WR_DIS                                  EFUSE_BLK0         0               8
     WR_DIS.RD_DIS                           EFUSE_BLK0         0               1
     WR_DIS.WDT_DELAY_SEL                    EFUSE_BLK0         1               1
     WR_DIS.DIS_PAD_JTAG                     EFUSE_BLK0         1               1
     WR_DIS.DIS_DOWNLOAD_ICACHE              EFUSE_BLK0         1               1
     WR_DIS.DIS_DOWNLOAD_MANUAL_ENCRYPT      EFUSE_BLK0         2               1
     WR_DIS.SPI_BOOT_CRYPT_CNT               EFUSE_BLK0         2               1
     WR_DIS.XTS_KEY_LENGTH_256               EFUSE_BLK0         2               1
     WR_DIS.SECURE_BOOT_EN                   EFUSE_BLK0         2               1
    WR_DIS.UART_PRINT_CONTROL               EFUSE_BLK0         3               1
    WR_DIS.FORCE_SEND_RESUME                EFUSE_BLK0         3               1
    WR_DIS.DIS_DOWNLOAD_MODE                EFUSE_BLK0         3               1
    WR_DIS.DIS_DIRECT_BOOT                  EFUSE_BLK0         3               1
    WR_DIS.ENABLE_SECURITY_DOWNLOAD         EFUSE_BLK0         3               1
    WR_DIS.FLASH_TPUW                       EFUSE_BLK0         3               1
    WR_DIS.SECURE_VERSION                   EFUSE_BLK0         4               1
    WR_DIS.CUSTOM_MAC_USED                  EFUSE_BLK0         4               1
    WR_DIS.DISABLE_WAFER_VERSION_MAJOR      EFUSE_BLK0         4               1
    WR_DIS.DISABLE_BLK_VERSION_MAJOR        EFUSE_BLK0         4               1
    WR_DIS.CUSTOM_MAC                       EFUSE_BLK0         5               1
    WR_DIS.MAC                              EFUSE_BLK0         6               1
    WR_DIS.WAFER_VERSION_MINOR              EFUSE_BLK0         6               1
    WR_DIS.WAFER_VERSION_MAJOR              EFUSE_BLK0         6               1
    WR_DIS.PKG_VERSION                      EFUSE_BLK0         6               1
    WR_DIS.BLK_VERSION_MINOR                EFUSE_BLK0         6               1
    WR_DIS.BLK_VERSION_MAJOR                EFUSE_BLK0         6               1
    WR_DIS.OCODE                            EFUSE_BLK0         6               1
    WR_DIS.TEMP_CALIB                       EFUSE_BLK0         6               1
    WR_DIS.ADC1_INIT_CODE_ATTEN0            EFUSE_BLK0         6               1
    WR_DIS.ADC1_INIT_CODE_ATTEN3            EFUSE_BLK0         6               1
    WR_DIS.ADC1_CAL_VOL_ATTEN0              EFUSE_BLK0         6               1
    WR_DIS.ADC1_CAL_VOL_ATTEN3              EFUSE_BLK0         6               1
    WR_DIS.DIG_DBIAS_HVT                    EFUSE_BLK0         6               1
    WR_DIS.DIG_LDO_SLP_DBIAS2               EFUSE_BLK0         6               1
    WR_DIS.DIG_LDO_SLP_DBIAS26              EFUSE_BLK0         6               1
    WR_DIS.DIG_LDO_ACT_DBIAS26              EFUSE_BLK0         6               1
    WR_DIS.DIG_LDO_ACT_STEPD10              EFUSE_BLK0         6               1
    WR_DIS.RTC_LDO_SLP_DBIAS13              EFUSE_BLK0         6               1
    WR_DIS.RTC_LDO_SLP_DBIAS29              EFUSE_BLK0         6               1
    WR_DIS.RTC_LDO_SLP_DBIAS31              EFUSE_BLK0         6               1
    WR_DIS.RTC_LDO_ACT_DBIAS31              EFUSE_BLK0         6               1
    WR_DIS.RTC_LDO_ACT_DBIAS13              EFUSE_BLK0         6               1
    WR_DIS.ADC_CALIBRATION_3                EFUSE_BLK0         6               1
    WR_DIS.BLOCK_KEY0                       EFUSE_BLK0         7               1
    RD_DIS                                  EFUSE_BLK0         32              2
    RD_DIS.KEY0                             EFUSE_BLK0         32              2
    RD_DIS.KEY0.LOW                         EFUSE_BLK0         32              1
    RD_DIS.KEY0.HI                          EFUSE_BLK0         33              1
    WDT_DELAY_SEL                           EFUSE_BLK0         34              2
    DIS_PAD_JTAG                            EFUSE_BLK0         36              1
    DIS_DOWNLOAD_ICACHE                     EFUSE_BLK0         37              1
    DIS_DOWNLOAD_MANUAL_ENCRYPT             EFUSE_BLK0         38              1
    SPI_BOOT_CRYPT_CNT                      EFUSE_BLK0         39              3
    XTS_KEY_LENGTH_256                      EFUSE_BLK0         42              1
    UART_PRINT_CONTROL                      EFUSE_BLK0         43              2
    FORCE_SEND_RESUME                       EFUSE_BLK0         45              1
    DIS_DOWNLOAD_MODE                       EFUSE_BLK0         46              1
    DIS_DIRECT_BOOT                         EFUSE_BLK0         47              1
    ENABLE_SECURITY_DOWNLOAD                EFUSE_BLK0         48              1
    FLASH_TPUW                              EFUSE_BLK0         49              4
    SECURE_BOOT_EN                          EFUSE_BLK0         53              1
    SECURE_VERSION                          EFUSE_BLK0         54              4
    CUSTOM_MAC_USED                         EFUSE_BLK0         58              1
    DISABLE_WAFER_VERSION_MAJOR             EFUSE_BLK0         59              1
    DISABLE_BLK_VERSION_MAJOR               EFUSE_BLK0         60              1
    USER_DATA                               EFUSE_BLK1         0               88
    USER_DATA.MAC_CUSTOM                    EFUSE_BLK1         0               48
    MAC                                     EFUSE_BLK2         0               8
    MAC                                     EFUSE_BLK2         8               8
    MAC                                     EFUSE_BLK2         16              8
    MAC                                     EFUSE_BLK2         24              8
    MAC                                     EFUSE_BLK2         32              8
    MAC                                     EFUSE_BLK2         40              8
    WAFER_VERSION_MINOR                     EFUSE_BLK2         48              4
    WAFER_VERSION_MAJOR                     EFUSE_BLK2         52              2
    PKG_VERSION                             EFUSE_BLK2         54              3
    BLK_VERSION_MINOR                       EFUSE_BLK2         57              3
    BLK_VERSION_MAJOR                       EFUSE_BLK2         60              2
    OCODE                                   EFUSE_BLK2         62              7
    TEMP_CALIB                              EFUSE_BLK2         69              9
    ADC1_INIT_CODE_ATTEN0                   EFUSE_BLK2         78              8
    ADC1_INIT_CODE_ATTEN3                   EFUSE_BLK2         86              5
    ADC1_CAL_VOL_ATTEN0                     EFUSE_BLK2         91              8
    ADC1_CAL_VOL_ATTEN3                     EFUSE_BLK2         99              6
    DIG_DBIAS_HVT                           EFUSE_BLK2        105              5
    DIG_LDO_SLP_DBIAS2                      EFUSE_BLK2        110              7
    DIG_LDO_SLP_DBIAS26                     EFUSE_BLK2        117              8
    DIG_LDO_ACT_DBIAS26                     EFUSE_BLK2        125              6
    DIG_LDO_ACT_STEPD10                     EFUSE_BLK2        131              4
    RTC_LDO_SLP_DBIAS13                     EFUSE_BLK2        135              7
    RTC_LDO_SLP_DBIAS29                     EFUSE_BLK2        142              9
    RTC_LDO_SLP_DBIAS31                     EFUSE_BLK2        151              6
    RTC_LDO_ACT_DBIAS31                     EFUSE_BLK2        157              6
    RTC_LDO_ACT_DBIAS13                     EFUSE_BLK2        163              8
    ADC_CALIBRATION_3                       EFUSE_BLK2        192              11
    KEY0                                    EFUSE_BLK3         0              256
    KEY0.FE_256BIT                          EFUSE_BLK3         0              256
    KEY0.FE_128BIT                          EFUSE_BLK3         0              128
    KEY0.SB_128BIT                          EFUSE_BLK3        128             128

Used bits in efuse table:
EFUSE_BLK0
[0 7] [0 1] [1 1] [1 2] [2 2] ... [6 6] [6 6] [6 6] [6 6] [6 6] [6 6] [6 6] [6 6] [6 6] [6 7] [32 33] [32 33] [32 60]
EFUSE_BLK1
[0 87] [0 47]
EFUSE_BLK2
[0 170] [192 202]
EFUSE_BLK3
[0 255] [0 255] [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:

Add a record for each eFuse field in CSV file.
Run the show_efuse_table command to check eFuse table.
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-C2 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
(...)

EFUSE_NAME (Block) Description  = [Meaningful Value] [Readable/Writeable] (Hex Value)
----------------------------------------------------------------------------------------
Calibration fuses:
OCODE (BLOCK2)                                     OCode                                              = 78 R/W (0b1001110)
TEMP_CALIB (BLOCK2)                                Temperature calibration data                       = -7.4 R/W (0b101001010)
ADC1_INIT_CODE_ATTEN0 (BLOCK2)                     ADC1 init code at atten0                           = 28 R/W (0x07)
ADC1_INIT_CODE_ATTEN3 (BLOCK2)                     ADC1 init code at atten3                           = 0 R/W (0b10000)
ADC1_CAL_VOL_ATTEN0 (BLOCK2)                       ADC1 calibration voltage at atten0                 = -44 R/W (0x8b)
ADC1_CAL_VOL_ATTEN3 (BLOCK2)                       ADC1 calibration voltage at atten3                 = 16 R/W (0b000100)
DIG_DBIAS_HVT (BLOCK2)                             BLOCK2 digital dbias when hvt                      = -16 R/W (0b10100)
DIG_LDO_SLP_DBIAS2 (BLOCK2)                        BLOCK2 DIG_LDO_DBG0_DBIAS2                         = -8 R/W (0b1000010)
DIG_LDO_SLP_DBIAS26 (BLOCK2)                       BLOCK2 DIG_LDO_DBG0_DBIAS26                        = 24 R/W (0x06)
DIG_LDO_ACT_DBIAS26 (BLOCK2)                       BLOCK2 DIG_LDO_ACT_DBIAS26                         = 16 R/W (0b000100)
DIG_LDO_ACT_STEPD10 (BLOCK2)                       BLOCK2 DIG_LDO_ACT_STEPD10                         = 12 R/W (0x3)
RTC_LDO_SLP_DBIAS13 (BLOCK2)                       BLOCK2 DIG_LDO_SLP_DBIAS13                         = 88 R/W (0b0010110)
RTC_LDO_SLP_DBIAS29 (BLOCK2)                       BLOCK2 DIG_LDO_SLP_DBIAS29                         = 96 R/W (0b000011000)
RTC_LDO_SLP_DBIAS31 (BLOCK2)                       BLOCK2 DIG_LDO_SLP_DBIAS31                         = 4 R/W (0b000001)
RTC_LDO_ACT_DBIAS31 (BLOCK2)                       BLOCK2 DIG_LDO_ACT_DBIAS31                         = 24 R/W (0b000110)
RTC_LDO_ACT_DBIAS13 (BLOCK2)                       BLOCK2 DIG_LDO_ACT_DBIAS13                         = 72 R/W (0x12)

Config fuses:
WR_DIS (BLOCK0)                                    Disable programming of individual eFuses           = 0 R/W (0x00)
RD_DIS (BLOCK0)                                    Disable reading from BlOCK3                        = 0 R/W (0b00)
UART_PRINT_CONTROL (BLOCK0)                        Set the default UARTboot message output mode       = Enable R/W (0b00)
DIS_DIRECT_BOOT (BLOCK0)                           This bit set means disable direct_boot mode        = False R/W (0b0)

Flash fuses:
FORCE_SEND_RESUME (BLOCK0)                         Set this bit to force ROM code to send a resume co = False R/W (0b0)
                                                   mmand during SPI boot
FLASH_TPUW (BLOCK0)                                Configures flash waiting time after power-up; in u = 0 R/W (0x0)
                                                   nit of ms. If the value is less than 15; the waiti
                                                   ng time is the configurable value.  Otherwise; the
                                                    waiting time is twice the configurable value

Identity fuses:
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_MINOR (BLOCK2)                       WAFER_VERSION_MINOR                                = 2 R/W (0x2)
WAFER_VERSION_MAJOR (BLOCK2)                       WAFER_VERSION_MAJOR                                = 1 R/W (0b01)
PKG_VERSION (BLOCK2)                               EFUSE_PKG_VERSION                                  = 1 R/W (0b001)
BLK_VERSION_MINOR (BLOCK2)                         Minor version of BLOCK2                            = With calib R/W (0b001)
BLK_VERSION_MAJOR (BLOCK2)                         Major version of BLOCK2                            = 0 R/W (0b00)

Jtag fuses:
DIS_PAD_JTAG (BLOCK0)                              Set this bit to disable pad jtag                   = False R/W (0b0)

Mac fuses:
CUSTOM_MAC_USED (BLOCK0)                           True if MAC_CUSTOM is burned                       = False R/W (0b0)
CUSTOM_MAC (BLOCK1)                                Custom MAC address
   = 00:00:00:00:00:00 (OK) R/W
MAC (BLOCK2)                                       MAC address
   = 08:3a:8d:5c:4b:94 (OK) R/W

Security fuses:
DIS_DOWNLOAD_ICACHE (BLOCK0)                       The bit be set to disable icache in download mode  = False R/W (0b0)
DIS_DOWNLOAD_MANUAL_ENCRYPT (BLOCK0)               The bit be set to disable manual encryption        = False R/W (0b0)
SPI_BOOT_CRYPT_CNT (BLOCK0)                        Enables flash encryption when 1 or 3 bits are set  = Disable R/W (0b000)
                                                   and disables otherwise
XTS_KEY_LENGTH_256 (BLOCK0)                        Flash encryption key length                        = 128 bits key R/W (0b0)
DIS_DOWNLOAD_MODE (BLOCK0)                         Set this bit to disable download mode (boot_mode[3 = False R/W (0b0)
                                                   :0] = 0; 1; 2; 4; 5; 6; 7)
ENABLE_SECURITY_DOWNLOAD (BLOCK0)                  Set this bit to enable secure UART download mode   = False R/W (0b0)
SECURE_BOOT_EN (BLOCK0)                            The bit be set to enable secure boot               = False R/W (0b0)
SECURE_VERSION (BLOCK0)                            Secure version for anti-rollback                   = 0 R/W (0x0)
BLOCK_KEY0 (BLOCK3)                                BLOCK_KEY0 - 256-bits. 256-bit key of Flash Encryp
   = 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
                                                   tion
BLOCK_KEY0_LOW_128 (BLOCK3)                        BLOCK_KEY0 - lower 128-bits. 128-bit key of Flash
   = 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 R/W
                                                   Encryption
BLOCK_KEY0_HI_128 (BLOCK3)                         BLOCK_KEY0 - higher 128-bits. 128-bits key of Secu
   = 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 R/W
                                                   re Boot

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

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 esp32c2"...
espefuse.py v4.6-dev
Connecting....
BLOCK0          (BLOCK0          ) [0 ] read_regs: 00000000 00000000
BLOCK1          (BLOCK1          ) [1 ] read_regs: 00000000 00000000 00000000
BLOCK2          (BLOCK2          ) [2 ] read_regs: 8d5c4b94 8252083a 5c01e953 80d0a824 c0860b18 00006890 00000000 4b000000
BLOCK_KEY0      (BLOCK3          ) [3 ] read_regs: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000

BLOCK0          (BLOCK0          ) [0 ] err__regs: 00000000 00000000
EFUSE_RD_RS_ERR_REG         0x00000000

=== Run "dump" command ===

Application Examples

system/efuse demonstrates how to use the eFuse API on ESP32-C2, 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/esp32c2/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.

Values:

enumerator EFUSE_BLK0: Number of eFuse BLOCK0. REPEAT_DATA

enumerator EFUSE_BLK1: Number of eFuse BLOCK1. SYS_DATA_PART0

enumerator EFUSE_BLK_SYS_DATA_PART0: Number of eFuse BLOCK2. SYS_DATA_PART0

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. KEY0. whole block

enumerator EFUSE_BLK_KEY0: Number of eFuse BLOCK3. KEY0. whole block

enumerator EFUSE_BLK_SECURE_BOOT

enumerator EFUSE_BLK_KEY_MAX

enumerator EFUSE_BLK_MAX: Number of eFuse blocks

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 purposes (they are virtual because this chip has only fixed purposes for block)

Values:

enumerator ESP_EFUSE_KEY_PURPOSE_USER: whole BLOCK3

enumerator ESP_EFUSE_KEY_PURPOSE_XTS_AES_128_KEY: FE uses the whole BLOCK3 (key is 256-bits)

enumerator ESP_EFUSE_KEY_PURPOSE_XTS_AES_128_KEY_DERIVED_FROM_128_EFUSE_BITS: FE uses lower 128-bits of BLOCK3 (key is 128-bits)

enumerator ESP_EFUSE_KEY_PURPOSE_SECURE_BOOT_V2: SB uses higher 128-bits of BLOCK3 (key is 128-bits)

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 arugments, 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: Tha 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.

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[(1U)]: 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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eFuse Manager

Introduction

eFuse Manager vs idf.py

Hardware Description

Defining eFuse Fields

Record Format

Structured eFuse Fields

efuse_table_gen.py Tool

Supported Coding Schemes

None Coding Scheme

RS Coding Scheme

Batch Writing Mode

eFuse API

How to Add a New Field

Bit Order

Get eFuses During Build

Debug eFuse & Unit Tests

Virtual eFuses

Flash Encryption Testing

espefuse.py

Application Examples

API Reference

Header File

Enumerations

Header File

Functions

Structures

Macros

Enumerations

eFuse Manager vs `idf.py`

`efuse_table_gen.py` Tool

`None` Coding Scheme

`RS` Coding Scheme

`espefuse.py`