va416xx-rs/bootloader/README.md

VA416xx Bootloader Application

This is the Rust version of the bootloader supplied by Vorago.

Memory Map

The bootloader uses the following memory map:

Address	Notes	Size
0x0	Bootloader start	code up to 0x3FFC bytes
0x3FFC	Bootloader CRC	word
0x4000	App image A start	code up to 0x1DFF8 (~120K) bytes
0x21FF8	App image A CRC check length	word
0x21FFC	App image A CRC check value	word
0x22000	App image B start	code up to 0x1DFF8 (~120K) bytes
0x3FFF8	App image B CRC check length	word
0x3FFFC	App image B CRC check value	word
0x40000	End of NVM	end

Additional Information

As opposed to the Vorago example code, this bootloader assumes a 40 MHz external clock but does not scale that clock up. It also uses a word (4 bytes) instead of a half-word for the CRC and uses the ISO 3309 CRC32 standard checksum.

This bootloader does not provide tools to flash the NVM memories by itself. Instead, you can use the flashloader application to perform this task using a CCSDS interface via a UART.

The bootloader performs the following steps:

1. The application will calculate the checksum of itself if the bootloader CRC is blank (all zeroes or all ones). If the CRC is not blank and the checksum check fails, it will immediately boot application image A. Otherwise, it proceeds to the next step.
2. Check the checksum of App A. If that checksum is valid, it will boot App A. If not, it will proceed to the next step.
3. Check the checksum of App B. If that checksum is valid, it will boot App B. If not, it will boot App A as the fallback image.

You could adapt and combine this bootloader with a non-volatile memory to select a prefered app image, which would be a first step towards an updatable flight software.

Please note that you MUST compile the application at slot A and slot B with an appropriate memory.x file where the base address of the FLASH was adapted according to the base address shown in the memory map above. The memory files to do this were provided in the scripts folder.