TIMG timers should support period mode

[bjoernQ]

Currently we only support target mode.

Period mode could be potentially useful e.g. esp-wifi currently uses period mode of SYSTIMER and since the HAL lacks that functionality it accesses the registers directly.

[MabezDev]

@bjoernQ I think this is already done for TIMG timers? When used with the e-h timer traits they are used in periodic mode? Please correct me if I'm wrong :D.

[bjoernQ]

🤔 seems you are right 👀 .... but probably it shouldn't be like that?

i.e. by default, it should be one-shot and we should have an "into_periodic" function (like systimer) to turn it into periodic mode?

[MabezDev]

I think that's just the way the e-h traits work, we implement periodic on the timer which has a cancel method to stop the timer at any point - i.e after one iteration.

I guess we could still have the into_periodic function on the timer, and implement the periodic trait on that type 🤔

[bjoernQ]

Sounds like the best way to go - then it's aligned with systimer 👍

[MabezDev]

We might struggle here, TimerGroup contains two timers (on most chips). We can't use into_periodic(self) on the timers inside, because we can't move the timers out of TimerGroup :/

[bjoernQ]

Ohh you are right

[MabezDev]

I think with that in mind lets close this for now. If the need for something like this pops up again, we can look at changing the whole TimerGroup struct