Flash layout on micro:bit V2

[kevinjwalters]

What's stored in the flash storage on the nRF52833 main microcontroller for MicroPython? When you compile it there's a handy little table at the end. Is this a complete picture? Why is there a gap at the beginning (0x00000 to 0x00fff)? Does anything else get put in the 0x73000 to 0x7ffff` gap?

SoftDevice   0x01000..0x1c000 110592 bytes
MicroPython  0x1c000..0x69174 315764 bytes
Layout table 0x69fc0..0x6a000 64 bytes
Filesystem   0x6d000..0x73000 24576 bytes

[shariltumin]

I assume you're using the "microbit-foundation/micropython-microbit-v2"

Try changing the src/codal_port/filesystem.ld and recompile.

/* Max size filesystem */
_fs_start = 0x6D000;
_fs_end = 0x7ffff;

Compiling with this gave me:

$ make
...
...
git -C ../lib/codal checkout CMakeLists.txt
Updated 1 path from the index
arm-none-eabi-size ../lib/codal/build/MICROBIT
   text	   data	    bss	    dec	    hex	filename
 314996	 140823	 120336	 576155	  8ca9b	../lib/codal/build/MICROBIT
python3 addlayouttable.py ./build/MICROBIT.hex ../lib/codal/build/MICROBIT.map -o ./MICROBIT.hex
SoftDevice    0x01000..0x1c000  110592 bytes
MicroPython   0x1c000..0x68e74  314996 bytes
Layout table  0x68fc0..0x69000      64 bytes
Filesystem    0x6d000..0x7ffff   77823 bytes

The gap at the beginning (0x00000..0x00fff) is for the bootloader.

I do not have microbit v2 board, so I cannot test the firmware.

[kevinjwalters]

I've been experimenting with changing the file system size and position. When I make it bigger it works for a while and then it gets corrupted after more file operations (in Thonny). That made me curious if there was anything else in the 0x7xxxx space conflicting with it.

Is there a bootloader on both the interface microcontroller and the main (target) microconctroller on the micro:bits?

[shariltumin]

I don't know, but there must be a good reason why the file system ends at 0x73000.

Perhaps other underlying subsystems are using the space between 0x73000 and 0x7ffff. My guess is as good as yours: bootloader, softdevice, codal_app, etc.