48 lines
2.2 KiB
Markdown
48 lines
2.2 KiB
Markdown
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VA416xx Bootloader Application
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=======
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This is the Rust version of the bootloader supplied by Vorago.
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## Memory Map
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The bootloader uses the following memory map:
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| Address | Notes | Size |
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| ------ | ---- | ---- |
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| 0x0 | Bootloader start | code up to 0x3FFC bytes |
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| 0x3FFC | Bootloader CRC | word |
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| 0x4000 | App image A start | code up to 0x1DFFC (~120K) bytes |
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| 0x21FFC | App image A CRC check length | word |
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| 0x21FFE | App image A CRC check value | word |
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| 0x22000 | App image B start | code up to 0x1DFFC (~120K) bytes |
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| 0x3FFFC | App image B CRC check length | word |
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| 0x3FFFE | App image B CRC check value | word |
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| 0x40000 | End of NVM | end |
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## Additional Information
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As opposed to the Vorago example code, this bootloader assumes a 40 MHz external clock
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but does not scale that clock up. It also uses a word (4 bytes) instead of a half-word for the CRC
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and uses the ISO 3309 CRC32 standard checksum.
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This bootloader does not provide tools to flash the NVM memories by itself. Instead, you can use
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the [flashloader](https://egit.irs.uni-stuttgart.de/rust/va416xx-rs/src/branch/main/flashloader)
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application to perform this task using a CCSDS interface via a UART.
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The bootloader performs the following steps:
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1. The application will calculate the checksum of itself if the bootloader CRC is blank (all zeroes
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or all ones). If the CRC is not blank and the checksum check fails, it will immediately boot
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application image A. Otherwise, it proceeds to the next step.
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2. Check the checksum of App A. If that checksum is valid, it will boot App A. If not, it will
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proceed to the next step.
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3. Check the checksum of App B. If that checksum is valid, it will boot App B. If not, it will
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boot App A as the fallback image.
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You could adapt and combine this bootloader with a non-volatile memory to select a prefered app
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image, which would be a first step towards an updatable flight software.
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Please note that you *MUST* compile the application at slot A and slot B with an appropriate
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`memory.x` file where the base address of the `FLASH` was adapted according to the base address
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shown in the memory map above. The memory files to do this were provided in the `scripts` folder.
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