ESP32 component: eFuse functions

An ESP-IDF component for managing the eFuses of the ESP32 on the MCH2022 badge.

Defines two functions:

void efuse_print_state()

Prints an incomplete report on the state of the eFuses to the console.

void efuse_protect()

1. Forces 3.3v operation for the SPI flash and PSRAM on the ESP32 module. The MCH2022 badge uses an "ESP32-WROVER-E" module. If your device uses a different module type (like the original non -E version of the "ESP32-WROVER") then you either want to modify this function or stay away from it all together as those modules use 1.8v flash and PSRAM.
2. Write protects all dangerous eFuses

eFuse summary after running the efuse protect function

espefuse.py v3.3-dev
EFUSE_NAME (Block) Description  = [Meaningful Value] [Readable/Writeable] (Hex Value)
----------------------------------------------------------------------------------------
Calibration fuses:
BLK3_PART_RESERVE (BLOCK0):                        BLOCK3 partially served for ADC calibration data   = False R/- (0b0)
ADC_VREF (BLOCK0):                                 Voltage reference calibration                      = 1107 R/- (0b00001)

Config fuses:
XPD_SDIO_FORCE (BLOCK0):                           Ignore MTDI pin (GPIO12) for VDD_SDIO on reset     = True R/- (0b1)
XPD_SDIO_REG (BLOCK0):                             If XPD_SDIO_FORCE, enable VDD_SDIO reg on reset    = True R/- (0b1)
XPD_SDIO_TIEH (BLOCK0):                            If XPD_SDIO_FORCE & XPD_SDIO_REG                   = 3.3V R/- (0b1)
CLK8M_FREQ (BLOCK0):                               8MHz clock freq override                           = 50 R/W (0x32)
SPI_PAD_CONFIG_CLK (BLOCK0):                       Override SD_CLK pad (GPIO6/SPICLK)                 = 0 R/- (0b00000)
SPI_PAD_CONFIG_Q (BLOCK0):                         Override SD_DATA_0 pad (GPIO7/SPIQ)                = 0 R/- (0b00000)
SPI_PAD_CONFIG_D (BLOCK0):                         Override SD_DATA_1 pad (GPIO8/SPID)                = 0 R/- (0b00000)
SPI_PAD_CONFIG_HD (BLOCK0):                        Override SD_DATA_2 pad (GPIO9/SPIHD)               = 0 R/- (0b00000)
SPI_PAD_CONFIG_CS0 (BLOCK0):                       Override SD_CMD pad (GPIO11/SPICS0)                = 0 R/- (0b00000)
DISABLE_SDIO_HOST (BLOCK0):                        Disable SDIO host                                  = False R/W (0b0)

Efuse fuses:
WR_DIS (BLOCK0):                                   Efuse write disable mask                           = 46701 R/W (0xb66d)
RD_DIS (BLOCK0):                                   Efuse read disable mask                            = 0 R/- (0x0)
CODING_SCHEME (BLOCK0):                            Efuse variable block length scheme                
   = NONE (BLK1-3 len=256 bits) R/- (0b00)
KEY_STATUS (BLOCK0):                               Usage of efuse block 3 (reserved)                  = False R/- (0b0)

Identity fuses:
MAC (BLOCK0):                                      Factory MAC Address                               
   = b8:f0:09:91:f6:a8 (CRC 0x4e OK) R/- 
MAC_CRC (BLOCK0):                                  CRC8 for factory MAC address                       = 78 R/- (0x4e)
CHIP_VER_REV1 (BLOCK0):                            Silicon Revision 1                                 = True R/- (0b1)
CHIP_VER_REV2 (BLOCK0):                            Silicon Revision 2                                 = True R/- (0b1)
CHIP_VERSION (BLOCK0):                             Reserved for future chip versions                  = 2 R/- (0b10)
CHIP_PACKAGE (BLOCK0):                             Chip package identifier                            = 1 R/- (0b001)
MAC_VERSION (BLOCK3):                              Version of the MAC field                           = 0 R/- (0x00)

Security fuses:
FLASH_CRYPT_CNT (BLOCK0):                          Flash encryption mode counter                      = 0 R/- (0b0000000)
UART_DOWNLOAD_DIS (BLOCK0):                        Disable UART download mode (ESP32 rev3 only)       = False R/- (0b0)
FLASH_CRYPT_CONFIG (BLOCK0):                       Flash encryption config (key tweak bits)           = 0 R/- (0x0)
CONSOLE_DEBUG_DISABLE (BLOCK0):                    Disable ROM BASIC interpreter fallback             = True R/- (0b1)
ABS_DONE_0 (BLOCK0):                               Secure boot V1 is enabled for bootloader image     = False R/- (0b0)
ABS_DONE_1 (BLOCK0):                               Secure boot V2 is enabled for bootloader image     = False R/- (0b0)
JTAG_DISABLE (BLOCK0):                             Disable JTAG                                       = False R/W (0b0)
DISABLE_DL_ENCRYPT (BLOCK0):                       Disable flash encryption in UART bootloader        = False R/- (0b0)
DISABLE_DL_DECRYPT (BLOCK0):                       Disable flash decryption in UART bootloader        = False R/- (0b0)
DISABLE_DL_CACHE (BLOCK0):                         Disable flash cache in UART bootloader             = False R/- (0b0)
BLOCK1 (BLOCK1):                                   Flash encryption key                              
   = 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 
BLOCK2 (BLOCK2):                                   Secure boot key                                   
   = 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 
BLOCK3 (BLOCK3):                                   Variable Block 3                                  
   = 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/- 

Flash voltage (VDD_SDIO) set to 3.3V by efuse.

But what if I want to play with efuses?

You're free to burn whatever you want to blocks 1 and 2, they've not been write protected but the read protection is permanently disabled by the protect function so they can always be read.

License

This ESP32 module has been written by Renze Nicolai and may be used under the terms of the MIT license.