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CONFIG.md

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Configuring bootloader

The bootloader can be configured by overriding defaults through parameters passed to make.

  • Use external file to override default settings
make DFU_USER_CONFIG=userconfig.h <targets>
  • Override settings directly
make DFU_BOOTSTRAP_PIN=2 DFU_CIPHER=DFU_CIPHER_XTEA DFU_VERIFY_CHECKSUM=FNV1A64 <targets>

You can find configuration parameters in the following tables. Defaults marked bold.

Table 1. Generic config

Parameter Description Values/Types Notes
DFU_USER_CONFIG Defines file with overrides filename not defined
DFU_DNLOAD_NOSYNC Disables DFU SYNC state _ENABLE/_DISABLE
DFU_INTF_EEPROM Enables EEPROM interface _ENABLE/_DISABLE/_AUTO
DFU_CAN_UPLOAD Enables uploads from device _ENABLE/_DISABLE
DFU_DETACH Enables DFU_DETACH command _ENABLE/_DISABLE Issues RESET on detach
DFU_VERIFY_CHECKSUM Enables checksum verification See Table 2 _DISABLE
DFU_VENDOR_ID USB Device VID UINT16 0x0483
DFU_DEVICE_ID USB Device DID UINT16 0xDF11
DFU_STR_MANUF USB Device manufacturer string ASCII/UTF-16 "Your company name"
DFU_STR_PRODUCT USB Device product string ASCII/UTF-16 "Secure bootloader"
DFU_DSC_CONFIG Enables Device configuration string _ENABLE/_DISABLE
DFU_STR_CONFIG Device configuration string ASCII/UTF-16 "DFU"
DFU_DSC_FLASH Enables flash interface string _ENABLE/_DISABLE
DFU_STR_FLASH Flash interface string ASCII/UTF-16 "Internal flash"
DFU_DSC_EEPROM Enables EEPROM interface string _ENABLE/_DISABLE
DFU_STR_EEPROM EEPROM interface string ASCII/UTF-16 "Internal EEPROM"
DFU_POLL_TIMEOUT DFU poll time (ms) > 0 20
DFU_DETACH_TIMEOUT DFU detach timeout (ms) > 0 200
DFU_BLOCKSZ DFU block size (bytes) must fit cipher block size 0x80
DFU_BOOTKEY DFU bootkey value UINT32 0x157F32D4
DFU_BOOTKEY_ADDR Address of the bootkey in RAM RAM ADDRESS/_DISABLE/_AUTO on the top of stack
DFU_BOOTSTRAP_GPIO DFU bootstrap port GPIOx/_DISABLE GPIOA
DFU_BOOTSTRAP_PIN DFU bootstarp pin 0-15 1
DFU_BOOTSTRAP_LEVEL Level on bootstrap pin to activate _LOW/_HIGH
DFU_BOOTSTRAP_PULL Bootstrap pin pullup control _DISABLE/_AUTO/_LOW/_HIGH
DFU_DBLRESET_MS Doublereset activation time (ms) TIMEOUT/_DISABLE 300
DFU_APP_START Start address for user code ROM ADDRESS/_AUTO must be page aligned
DFU_APP_SIZE User application max size AMMOUNT/_AUTO up to the ROM end
DFU_CIPHER Type of ciper See Table 3 DFU_CIPHER_RC5
DFU_CIPHER_MODE Cipher mode of operation See Table 4 DFU_CIPHER_CBC
DFU_AES_KEY_128 128-bit cipher key Comma separated bytes
DFU_AES_KEY_256 256-bit cipher key Comma separated bytes
DFU_AES_IV_64 64-bit cipher IV Comma separated bytes
DFU_AES_IV_96 96-bit cipher IV Comma separated bytes Used for the CHACHA
DFU_AES_IV_128 128-bit cipher IV Comma separated bytes

Table 2. Available Checksums

Note: Firmware checksum will be checked on every startup. Bootloader will be activated if no correct firmware found. It may take a lot of time.

Checksum Description
_DISABLE Disable firmware verification
CRC32FAST Lookup table based crc32 algorithm, consumes 1Kb of RAM for the table
CRC32SMALL Permutation based crc32 algorithm, no lookup table required but slower
FNV1A32 Fowler–Noll–Vo 32 bit Hash
FNV1A64 Fowler–Noll–Vo 64 bit Hash
CRC64FAST Lookup table based crc64 algorithm, consumes 2Kb of RAM for the table
CRC64SMALL Permutation based crc64 algorithm, no lookup table required but extremly slow

Table 3. Available Ciphers

Cipher Type/Mode Description Block size Key Size IV size Notes
_DISABLE Disable encryption
DFU_CIPHER_ARC4 Rivest RC-4 Stream 128 N/A Unsafe
DFU_CIPHER_CHACHA RFC7539-CHACHA20 Stream 256 96
DFU_CIPHER_CHACHA_A RFC7539-CHACHA20 Stream 256 96 THUMB ASM version
DFU_CIPHER_GOST GOST R 34.12-2015 MAGMA 64 256 64 treat data as LE64
DFU_CIPHER_MAGMA GOST R 34.12-2015 MAGMA 64 256 64
DFU_CIPHER_RAIDEN RAIDEN 64 128 64
DFU_CIPHER_RC5 Rivest RC5-32/12/128 64 128 64
DFU_CIPHER_RC5_A Rivest RC5-32/12/128 64 128 64 THUMB ASM version
DFU_CIPHER_SPECK SPECK 64/128 64 128 64
DFU_CIPHER_XTEA XTEA 64 128 64 treat data as LE32
DFU_CIPHER_XTEA1 XTEA-1 64 128 64 treat data as LE32
DFU_CIPHER_BLOWFISH Blowfish 64 256 64 Uses xorshift instead PI
DFU_CIPHER_RTEA Ruptor's TEA or Repaired TEA 64 256 64
DFU_CIPHER_RC6 Rivest RC6-32/20/16 128 128 128
DFU_CIPHER_RC6_A Rivest RC6-32/20/16 128 128 128 THUMB ASM verison
DFU_CIPHER_RIJNDAEL Rijndael AES-128/192/256 128 128 128 128-bit key by default

Table 4. Available Block Cipher Modes of Operation

Cipher mode Description
DFU_CIPHER_ECB Electronic Codebook (ECB)
DFU_CIPHER_CBC Cipher Block Chaining (CBC)
DFU_CIPHER_PCBC Propagating Cipher Block Chaining (PCBC)
DFU_CIPHER_CFB Cipher Feedback (CFB)
DFU_CIPHER_OFB Output Feedback (OFB)
DFU_CIPHER_CTR Counter (CTR) (simply IV increment)