[feature] reset to DFU mode in software

[hdhoang]

I would like to initiate reset to DFU without having to flip the keyboard and poke the reset pin. AIUI, booting with the Escape key down enters DFU mode, so I imagined binding a key-combo with Escape to reset the key MCU would do the job.

In https://github.com/hdhoang/anne-key/commit/13c9604c1b0da2c9d9411ea85422d932fed25a6e I have given the SCB to Keyboard, then tried to write the reset request when processing Action::Reset. Though the set_theme(3) call worked, the keyboard went on working normally instead of resetting.

Some paths I would like to explore next:

• maybe I need to write to AIRCR differently?
• maybe I need to move SCB base back to bootloader's position so that the CPU starts there after reset?

Nikkelitous also said people normally reset MCU from the host side instead of requesting it to reset itself :)

Please advise me on how to implement this!

[ah-]

This looks about right to me.

Possibly unsafe { scb.aircr.modify(|v| v | (0x05fa << 16) | 0b100) } has some bits set in v that you might not want, maybe try just unsafe { scb.aircr.modify(|v| (0x05fa << 16) | 0b100) }?

Register key:

Reads as 0xFA05

On writes, write 0x5FA to VECTKEY, otherwise the write is ignored.```

[hdhoang]

Thanks for the review. I started out with write(0x05fa_0004), then adapted an SO's answer mask-preserving write into the modify call. Neither had the desired effect.

However there's a difference between overwriting and modifying:

• overwrite: the LEDs turn off while the Reset key is held down, and turn back on when released
• modify: the first set_theme call runs

I'll try adding some syst.cvr waiting to see further effect.

[ah-]

Sounds like the overwrite method is working. Not sure what exactly it resets, maybe it just runs user code again?

Maybe put something into main.rs init so you can see? It should now turn on leds on startup.