Question about customized task for GPIOTE

[Jinyue Zhu]

Hi,

I was writing a program that uses the PPI with event from the timer and the task to one of the GPIO pins. The ideal scenario is that, whenever the timer fires, it will trigger the task and cause the GPIO pin to do a customized behavior (for example, turn on, then turn off, and turn on again).

I was aware that there are some default behavior (tasks) that can be used, such as GPIO_CONFIG_OUT_TASK_TOGGLE. I wonder if there is a way to define a task myself, so that I can update that pin many times in a customized way for each triggering event.

Thanks,

Jinyue

[Håkon Alseth]

Hi,

 

I was writing a program that uses the PPI with event from the timer and the task to one of the GPIO pins. The ideal scenario is that, whenever the timer fires, it will trigger the task and cause the GPIO pin to do a customized behavior (for example, turn on, then turn off, and turn on again).

 You can setup the NRF_TIMERx to trigger several EVENTS_COMPARE[], which you connect using PPI channels.

If you need a specific timer to trigger the "start" sequence, you likely have to use two timers.

 

The NRF_TIMERy runs every 500 ms (then generates EVENTS_COMPARE[0], where this is shorted in NRF_TIMERy->SHORTS to restart the timer), for instance.

You take that event NRF_TIMERy->EVENTS_COMPARE[0], and route that to start the next NRF_TIMERx.

You could for instance setup NRF_TIMERx like this:

1. EVENTS_COMPARE[0] happens after 100 ms

2. EVENTS_COMPARE[1] happens after 250 ms (delta = 250-100=150ms)

3. EVENTS_COMPARE[2] happens after 500 ms

Each event should then have a corresponding PPI channel, with a defined GPIOTE task (set, clear or toggle)

The last event occurring (time-wise) should be the one configured to restart the counter (see the SHORTS.COMPAREx_CLEAR mask here)

If you need two things to occur from the same event, see PPI fork functionality.

 

I was aware that there are some default behavior (tasks) that can be used, such as GPIO_CONFIG_OUT_TASK_TOGGLE. I wonder if there is a way to define a task myself, so that I can update that pin many times in a customized way for each triggering event.

PPI only routes events to tasks. If you cannot generate an event, or set the functionality using one task; then it cannot be done with PPI.

 

Kind regards,

Håkon

[Jinyue Zhu]

Hi Håkon,

Thanks for this update. For the question on disabling the timer in its own compare_event, I am wondering if there's a sample code that demonstrates this. Thanks for the help!

[Håkon Alseth]

Hi,

 

You essentially have this in the function "timer_event_handler" that you posted earlier. You just need to add a counter to that logic.

 

Kind regards,

Håkon