Firmware-assisted flashing

[algernon]

Is your feature request related to a problem? Please describe.

Currently, when we're flashing, a fair number of our supported keyboards require one to hold a key during reset, to enter bootloader mode. During this time, whatever the key is mapped to, will appear held, which may not be desirable. We can ignore some keys, but that only helps until the key stays mapped to the ones we ignore.

Describe the solution you'd like

I would like to propose a firmware-assisted flashing procedure. The way it would work, is that Chrysalis would signal the keyboard that reset is about to happen, and in response, the keyboard would suspend sending USB reports until reset, or a timeout, or an explicit ask to resume.

In practice, this would mean that no matter what the PROG key is mapped to, it will not interfere with anything, because it will not be reported.

As an alternative, we could restrict the suspension to the PROG key alone - that would require a bit more work on the firmware side, but might end up being more user friendly.

[obra]

This makes sense to me. I do think it should be timeout/ask-to-resume.

We should -probably- restrict it to the Prog / lockout key. Otherwise, the user can't hit return to trigger flashing.