Migrating from PPI to DPPI

[Yaxit]

I'm trying to port a PPI application to an nrf5340. I'm quite puzzled, as it would appear there is no obvious way to achieve what I'm trying to do.

In short, I have a setup where the events E should trigger tasks T accordingly to the relation below. Events originate by timers (E1-4 TIM3, E5 TIM4), and the tasks are simple GPIOTE clear/set

e1 --> t1,t5
e2 --> t2,t6
e3 --> t3,t5
e4 --> t4,t6
e5 --> t2,t4,t6

I'm using the gppi API, as I would like to support both nrf52 and nrf53 families. As far as I understand DPPI does not allow to associate multiple channels to the same task/event. This seems to make it impossible to achieve, as either tasks or events need to be connected to multiple channels.

I think I'm missing something since this was feasible with PPI and does not seem like a very strange use case to me :D

Thanks!

[Emil Lenngren]

Exactly which events are you listening to? Which event is which cc and do you have any shorts from a cc to clear (which in that case)?

[Yaxit]

- e1 to e4 are TIM3 CC0-3
- e5 is TIM4 CC0

- t1, t3, t5 are GPIOTE set
- t2, t4, t6 are GPIOTE clear

[Emil Lenngren]

At what point are you clearing (restarting) the timer instances? By ppi or from cpu?

[Yaxit]

For now in software. Later I would like to stop and clear tim3 on the e5 (tim4 cc0).
However again, the issue is mainly with the GPIOTE tasks. Clearing the timer would just add a few other tasks to the event e5.

[Emil Lenngren]

I think you should be able to use an EGU peripheral to form additional "edges" between channels (up to 16 per EGU instance). From what I see, DPPI groups as Maria suggests are more meant as a way to be able to enable/disable channels also from DPPI events, but not a way to give flexibility to event/task connectivity.

Example:

DPPI channel 0: e1 -> t1 & EGU.TASKS[0]

DPPI channel 1: e2 & EGU.EVENTS[4] -> t2 & EGU.TASKS[1]

DPPI channel 2: e3 -> t3 & EGU.TASKS[2]

DPPI channel 3: e4 & EGU.EVENTS[5] -> t4 & EGU.TASKS[3]

DPPI channel 4: EGU.EVENTS[0] & EGU.EVENTS[2] -> t5

DPPI channel 5: EGU.EVENTS[1] & EGU.EVENTS[3] -> t6

DPPI channel 6: e5 -> TIMER3->CLEAR & EGU.TASKS[4] & EGU.TASKS[5]

Then also configure a SHORTS from your TIMER4 CC0 to TIMER4 CLEAR.

See the following illustrature. Circles are DPPI channels and the horizontal lines are EGU task/events pairs.

[Yaxit]

I did not know of this peripheral, but it seems the layer of indirection that I need, I'll have a try and come back to you to confirm!

Thanks!

[Yaxit]

Sorry for the long wait. I finally had the change to try this approach with the EGU and it works well. I will close the ticket, thanks for the help!