Unable to use a DPPI group that disable itself

RE: Unable to use a DPPI group that disable itself

Nicolas Brunner — Mon, 18 Jan 2021 08:57:20 GMT

Thanks for the solution.

It would be great to also add this information in the documentation of the nrfx_dppi_channel_include_in_group() function. And maybe also make it return an error if the subscribe registers are not disabled.

RE: Unable to use a DPPI group that disable itself

Håkon Alseth — Fri, 15 Jan 2021 15:14:23 GMT

A small update.

The strict ordering is a hardware restriction, as explained in the DPPIC part of the PS:

https://infocenter.nordicsemi.com/topic/ps_nrf5340/dppi.html?cp=3_0_0_6_8_1#concept_crl_ql5_v1b

In order to write to CHG[x], the corresponding CHG[x].EN and CHG[x].DIS subscribe registers must be disabled. 
Writes to CHG[x] are ignored if any of the two subscribe registers are enabled.

Kind regards,

Håkon

RE: Unable to use a DPPI group that disable itself

Håkon Alseth — Fri, 15 Jan 2021 15:06:58 GMT

Hi,

My apologies for the long wait. Reproducing the issue was easy, but finding a fix for the problem took a bit of time.

It seems that you have to include the dppi channel into the group before subscribing to the disable task:

    ...
    nrfx_dppi_channel_include_in_group(channel, group);
    nrf_dppi_subscribe_set(NRF_DPPIC, nrf_dppi_group_disable_task_get(group), channel);
    ...

I slightly modified your test code, changing the base frequency and print "0" and "1" from the timer interrupt.

Here's my code:

devzone.nordicsemi.com/.../33657.main.c

Which should print in this order:

10110110110....

Could you see if you get the correct behavior when switching the order of the above two functions?

Kind regards,

Håkon