Finished flashloader and bootloader implementation

bootloader/README.md

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+VA108xx 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 |
+| 0x2FFE | Bootloader CRC | word |
+| 0x3000 | App image A start | code up to 0xE7F8 (~58K) bytes |
+| 0x117F8 | App image A CRC check length | word |
+| 0x117FC | App image A CRC check value | word |
+| 0x11800 | App image B start | code up to 0xE7F8 (~58K) bytes |
+| 0x1FFF8 | App image B CRC check length | word |
+| 0x1FFFC | App image B CRC check value | word |
+| 0x20000 | End of NVM | end  |
+
+## Additional Information
+
+This bootloader was specifically written for the REB1 board, so it assumes a M95M01 ST EEPROM
+is used to load the application code. The bootloader will also delay for a configurable amount
+of time before booting. This allows to catch the RTT printout, but should probably be disabled
+for production firmware.
+
+This bootloader does not provide tools to flash the NVM memory by itself. Instead, you can use
+the [flashloader](https://egit.irs.uni-stuttgart.de/rust/va108xx-rs/src/branch/main/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.