Accessing system clock(s) about qmk_firmware

[jackhumbert]

Yeah! I was meaning to reply on reddit, but this is much better :)

By default, I believe Timer 1 Timer 0 is always running, so you should be able to grab TCNT1 TCNT0 to use for that. You could also set up 0 1, 3, or 4 as well! There's some nice info on the timers here - the chip on the PCB/Teensy 2.0 is the Atmega32u4 if you need to find any specific info about it.

This is pretty awesome, though - let us know what happens!

[mecanogrh]

Timer0 is already in use in tmk code maybe not the best idea to use it.
See timer_avr.h and timer.c in tmk_core/common/avr.

[jackhumbert]

Sorry, that's the one I meant! I believe it's safe to read from TCNT0 without affecting anything that's going on.

[cbbrowne]

I'm grabbing the bottom 8 bits of TCNT1, and am finding it populated, for what it's worth.
I shut off my linear congruential RNG bit, and just used values from TCNT1, and was getting decently variable keystrokes, so it seems as though TCNT1 is being turned on.

With the combination of both RNGs (linear congruential, and XOR in bits from the counter), I'm certainly getting stuff looking random.

Here's some digits... 471074697342030825391029594704832

Here's some letters... xczqlozosvuslrmxcsbctuwtujsszbrwdzieoeegxssvqvecegszwaavkf

Looking good! Thanks, very helpful!

[jackhumbert]

That's great! Feel free to open a PR when you get things finalised :)

[mecanogrh]

Was looking at your code cbbrowne and wondered where you put the timer init, looks like Timer1 is used by the backlight sleep code. But as you only need a read (thought you wanted to tailor the timer as well) you could have use Timer0 as well I guess. Sorry for the misunderstanding and noise guys.