125 lines
4.3 KiB
Plaintext
125 lines
4.3 KiB
Plaintext
I2C interface to the firmware
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-----------------------------
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To control the operation of the keyboard's firmware, the firmware
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exposes some "registers" that the user can read/write using the
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two kinds of I2C transfers.
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1) set values of consecutive block of registers starting from REG_ADDR:
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START TX(DEV_ADDR+WR REG_ADDR [REG_DATA REG+1_DATA REG+2_DATA ...]) STOP
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2) read values of consecutive block of registers starting from REG_ADDR:
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START TX(DEV_ADDR+WR REG_ADDR) STOP
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START TX(DEV_ADDR+RD) RX(REG_ADDR [REG_DATA REG+1_DATA REG+2_DATA ...]) STOP
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Device address is 0x15.
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Registers
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---------
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0x00: Device ID1 (0x4b)
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0x01: Device ID2 (0x42)
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0x02: Firmware revision
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0x03: System configuration
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bit 0: disable KB scanning (1: scanning disabled, 0: scanning enabled)
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bit 1: poll mode
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1: don't rely on row change detection, poll the matrix periodically
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(prevents MCU power down)
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0: power down the MCU when no key is pressed, and rely on change
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detection on row inupts to wake the MCU up
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bit 2: enable USB debug interface
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1: enabled
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0: disabled
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0x10: Keyboard data for column 1
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...
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0x0b: Keyboard data for column 12
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0x0c: CRC8 of keyboard data from 0x10-0x0b
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0x20: Writing value 0x53 ('S') to this register stops the main app from
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jumping to the user app.
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0x70: Flashing mode unlock key
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(writing 0x46 to this register unlocks the flashing mode.)
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0x71: Flashing control
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Writing various commands to this register makes the MCU execute them,
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if the MCU is not executing the previous command. Available commands:
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0x52 - read a block of data from code ROM
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0x57 - write a block of data to code ROM
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0x45 - erase the code rom memory block (128B)
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0x43 - confirm the validity of the firmware and enable redirection
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to it from the main app (this redirection is automatically
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disabled before executing the 0x57 command)
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This register will ignore further commands as long as the last operation
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is still in progress. This register will contain the code of the
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currently executed operation, and will be cleared after the operation
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finishes. Completion is also signalled by pulsing the INT pin shortly.
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If the operation fails, this register will contain value 0xff. If it
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succeeds it will contain value 0x00.
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0x7d: target address low byte
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0x7e: target address high byte
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0x7f: CRC8 calculated for the 128B block of data from 0x80-0xff
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- this must be written by the user when preparing data for write
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operation, MCU checks the CRC8 of the data and compares it against
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the value in this register before starting the execution of
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0x57 command
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- this is updated by the MCU after reading the data from flash memory
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0x80: 128B block of EEPROM data (either read from code memory or to be
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... written)
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0xff
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Usage
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-----
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User can modify register 0x03 to choose how the firmware should operate.
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The settings are not persistent across resets.
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To read the keyboard matrix status, the user can perform a 13B read transaction
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from address 0x10 and calculate CRC8 on the first 12 bytes and compare it with
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the 13th byte.
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Bit 0 corresponds to row 1, bit 5 to row 6, bits 6 and 7 are always 0.
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Flashing
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--------
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The firmware is split into 3 parts:
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0x0000 - 0x2000: Stock USB bootloader
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0x2000 - 0x4000: Stock FOSS firmware (flashable from stock bootloader)
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0x4000 - 0x8000: User app (optional, flashable over I2C from stock FOSS firmware)
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When the stock FOSS firmware runs after MCU powerup or reset, it will wait for 200ms
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and listen on I2C. If 0x53 is not written to register 0x20 during that time and
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the user's app is flashed and commited, it will redirect interrupt vectors to
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0x4000+offset and jump to 0x4000, which will start executing user's app.
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User app should always return value 0x00 when reading register 0x20, to make it
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easy to distinguish that the "stay in stock app" command succeeded.
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Flashing steps:
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1) Unlock by writing 0x46 to register 0x70
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2) Write address to 0x7d/0x7e
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3) Write data to 0x80-0xff and CRC8 to 0x7f
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4) Write command 0x57 to 0x71
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5) Poll 0x71 for result (either 0x00 or 0xff)
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... repeat 2-5 for all memory locations to be flashed
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6) Write command 0x43 to reg 0x71
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7) Wait for success
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Reset the MCU.
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