Verified TBYB flag works as intended

[devYaoYH]

build and flashing sequence:

Load the partition table

picotool load ota_mvp/pt.uf2 -f
picotool reboot

First build the 'main' version of the code that will call reboot into the second partition

bazel build //ota_mvp:ota --config=pico
picotool load bazel-bin/ota_mvp/ota.uf2 -p 0 -f

Then build the new version of the code that will have Try-Before-You-Buy (TBYB) flag set

bazel build //ota_mvp:ota --config=ota-blink
picotool load bazel-bin/ota_mvp/ota.uf2 -p 1 -f

Now you can reboot which will start the code executing in partition 0 for ~6s (with led turned on constantly)

picotool reboot

At the end of ~6s it will call rom_reboot into partition 1 (with led blinking) for around 17s (watchdog timer). Since we never call explicit_buy, this software watchdog timer will reboot us back into partition 0!

[QuackWifHat]

LGTM

[devYaoYH]

Thanks for the fix to write partition bytes! I've verified that the writing actually works \o/ @QuackWifHat

[devYaoYH]

@QuackWifHat This is a static memory offset to the partition 1 starting address? So assuming we change the partition table, it would no longer work?

[devYaoYH]

See comment below, we can also extract this using a combination of rom_get_partition_table_info and rom_get_b_partition calls.

[QuackWifHat]

Yes that is correct, it would stop working if we change the partition table. It would be better to move this to a more dynamic call, like rom_get_partition_table_info, I will try allocating some cycles to get on this soon.

[devYaoYH]

We could also potentially extract the b_partition address offset dynamically:

[13:02:19.675] Partition Table Information:
[13:02:19.678] ----------------------------
[13:02:19.681] Has partition table: Yes
[13:02:19.684] Number of partitions: 3
[13:02:19.686] Partition 0:
[13:02:19.688]   Location: 0x00002000 (8 KB from flash start)
[13:02:19.692]   Size: 256 KB
[13:02:19.694] Partition 1:
[13:02:19.696]   Location: 0x00042000 (264 KB from flash start)
[13:02:19.701]   Size: 256 KB
[13:02:19.702] Partition 2:
[13:02:19.704]   Location: 0x00082000 (520 KB from flash start)
[13:02:19.709]   Size: 15860 KB
[13:02:19.711] === End of Partition Table ===
[13:02:19.714] Raw partition table data dump:
[13:02:19.717]   [0] 0x00000011
[13:02:19.719]   [1] 0x00000103
[13:02:19.721]   [2] 0xffffe000
[13:02:19.723]   [3] 0xfc008000
[13:02:19.725]   [4] 0xfc082002
[13:02:19.727]   [5] 0xfc021001
[13:02:19.729]   [6] 0xfc102042
[13:02:19.731]   [7] 0xfc021003
[13:02:19.733]   [8] 0xfdffc082
[13:02:19.735]   [9] 0xfc011001
[13:02:19.737] Boot info word from sys_info: 0x000000ff
[13:02:19.741] Get recent boot diagnostic from sys_info: 00000000
[13:02:19.746] B partition index of A/B partitioning scheme: 1
[13:02:19.751] Extracted B partition location from partition table: 0x00042000

Not an issue if we never commit to a newer version with explicity_buy, but might become an issue when we do.