A silly question about timer register triggers

[matangk]

I'm sorry. This must be trivial to all of you. I'm a beginner with nrf52 programming, and I saw several examples that refer to timers TASK_START, TASK_CLEAR, TASK_STOP. Everywhere, it just sets them to "1". However the datasheet says that it's a trigger operation (edge triggered as I understand it).

So.. What resets the trigger flag then? Is it automatic? After how many clock cycles? I searched in the datasheet and online tutorials but I'm clearly missing the answer.

Thanks in advance.

[Elfving]

Hey again,

I'm sorry.

No problem at all!

So.. What resets the trigger flag then?

It isn't edge triggered.

Those are write only registers, they won't be reset back to zero. Every time you write 1 to the register the internal task gets activated. which starts the internal task signal. You don't have to worry about resetting them to 0, or worry about activating them too frequently.

Regards,

Elfving

[matangk]

Ok.. thanks. A bit cryptic there.. So edge triggered or not it must have some auto-reset, I guess?

[Nguyen Hoan Hoang]

No, you reset it by writing a 0 to the EVENTS_?? registers.  EVENTS_COMPARE[I] = 0 for triggered events.  EVENTS_OVRFLW = 0 to reset overflow events

See implementation here 

Low freq clock : https://github.com/IOsonata/IOsonata/blob/master/ARM/Nordic/src/timer_lf_nrfx.cpp

High freq clock : https://github.com/IOsonata/IOsonata/blob/master/ARM/Nordic/src/timer_hf_nrfx.cpp

[matangk]

So.. resetting the match compare resets the timer task registers? It makes sense since resetting the match should in practice indicate the end of a desired timer operation. Though not very intuitive for me.. Thanks!

[Nguyen Hoan Hoang]

not totally, that reset the trigger interrupt.  To stop the trigger completely is another thing. see the disable trigger function

[Elfving]

For more info on the TIMER you can read about it in the product specification. You can think of it as it being automatically reset after one clock cycle, but it isn't edge triggered. It is guaranteed to take effect within one clock cycle.

Regards,

Elfving