Updatable firmware over I2C

[ardangelo]

Starting with Beepy firmware 3.0, firmware is loaded in two stages.

The first stage is a modified version of pico-flashloader.
It allows updates to be flashed to the second stage firmware while booted.

The second stage is the actual Beepy firmware.

Reading REG_UPDATE_DATA will return an update status code

• UPDATE_OFF = 0
• UPDATE_RECV = 1
• UPDATE_FAILED = 2
• UPDATE_FAILED_LINE_OVERFLOW = 3
• UPDATE_FAILED_FLASH_EMPTY = 4
• UPDATE_FAILED_FLASH_OVERFLOW = 5
• UPDATE_FAILED_BAD_LINE = 6
• UPDATE_FAILED_BAD_CHECKSUM = 7

Firmware updates are flashed by writing byte-by-byte to REG_UPDATE_DATA:

• Header line beginning with + e.g. +Beepy
• Followed by the contents of an image in Intel HEX format

By default, REG_UPDATE_DATA will be set to UPDATE_OFF.
After writing, REG_UPDATE_DATA will be set to UPDATE_RECV if more data is expected.

If the update completes successfully:

• REG_UPDATE_DATA will be set to UPDATE_OFF
• Shutdown signal will be sent to the Pi
• Delay to allow the Pi to cleanly shut down before poweroff (configurable with REG_SHUTDOWN_GRACE)
• Firmware is flashed and the system is reset

Please wait until the system reboots on its own before removing power.

If the update failed, REG_UPDATE_DATA will contain an error code and the firmware will not be modified.

The header line +... will reset the update process, so an interrupted or failed update can be retried by restarting the firmware write.

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After building firmware:

• build/app/i2c_puppet.uf2: flashable image with preloaded and Beepy firmware
• build/app/firmware.hex: Intel HEX format Beepy firmware (add the header line +Beepy to the beginning of the file before writing)