[Feature Request] Provide RGBLED_SPLIT like functionality for RGB_MATRIX

[tyalie]

Feature Request Type

• Core functionality
• Add-on hardware support (eg. audio, RGB, OLED screen, etc.)
• Alteration (enhancement/optimization) of existing feature(s)
• New behavior

Description

My understanding is, that as of now, there is no way to synchronize both halves of a split keyboard, when using the RGB_MATRIX functionality. On the other hand, RGB_LIGHT seems to support it.

[tyalie]

Okay. I got it working. Animations change on both sides, they know their relative position to each other, ...
Only problem now is, that they get heavily out of sync over time.

I've (as of now) no idea how fix that.

[tyalie]

Current idea: I know that the timer depends on the internal clock timer_read32 and that this is very imprecise on micro controllers. One idea would be to do a hand shake once in a while between both parties to calculate the time difference between the boards and apply that to the timer function.

[tyalie]

See #9613