DPPI NRFX Support NRF54L15

[LukeC]

DPPI is not able to build with SDK 2.8.

The issue seems to be the NRF54L15 has 4 DPPI peripherals, yet the NRFX hal version 2.8 only works with one.

// Driver for single instance DPPI
#if NRFX_CHECK(NRFX_DPPI_ENABLED) && (!defined(DPPIC_COUNT) || (DPPIC_COUNT == 1))

Would it be recommended to clone the latest release of the NRFX hal to get support for the 54L15?

github.com/.../nrfx_dppi.c

[Hung Bui]

Hi Luke, 
If you take a look at \zephyr\modules\hal_nordic\nrfx\CMakeLists.txt  you can find this:

So nrfx_gppi_dppi_ppib_lumos.c is used, not nrfx_dppi.c. 

[LukeC]

Hmm, so it looks like I should be using the "gppi" library -  #include <helpers/nrfx_gppi.h> then correct?  

I am trying to create multiple low-power PWM on the 54L15 with the GRTC and the GPIOTE.  I could do this on the 52 series, however this had a dedicated RTC that I could use for PWM.  With the 54L, it looks like there is just one global RTC with multiple CC channels.  is it still possible set up multiple low power PWMs using the GRTC and GPIOTE with the PPI events/tasks?   

[Hung Bui]

LukeC said:

I should be using the "gppi" library -  #include <helpers/nrfx_gppi.h> then correct?  

Correct. 

LukeC said:

I am trying to create multiple low-power PWM on the 54L15 with the GRTC and the GPIOTE.  I could do this on the 52 series, however this had a dedicated RTC that I could use for PWM.  With the 54L, it looks like there is just one global RTC with multiple CC channels.  is it still possible set up multiple low power PWMs using the GRTC and GPIOTE with the PPI events/tasks?   

I don't think it's a problem. I haven't tried to test connecting the CC event to GPIOTE via GPPI but I assume it should work. Note that there is a PWM on the GRTC that you may want to use directly. 

[LukeC]

Hung Bui said:

Note that there is a PWM on the GRTC that you may want to use directly. 

Yes, I think that will work for some projects, however, this project I need 4 low-power PWM's.  Ideally, I would like to be able to set their frequency a bit higher at 1khz which should be doable from the LF_RC clock source.

Question: Is there an event to restart a CC channel on the GRTC using the PPI?

My plan was as follows:

CC0 - PWM duty factor CC channel, on event set pin 

CC1 - PWM base clock channel, on event clear pin

I have this working, but each of these CC channels is one shot only,

I need a way to set up a GPPI channel to restart CC0/CC1 on a CC1 event.  I only see capture tasks as a possible task endpoint for the PPI to connect to.  It seems like I need a CC1 restart task to accomplish this.

Perhaps my approach is flawed? Is there a better way to configure the GRTC through the PPI to create a very low-power PWM?

I saw CC[0] allows for an interval periodic setting. I might be able to make a PWM using a toggle task on the GPIOTE, but that is only one channel.

[Hung Bui]

Hi Luke, 
Could you explain a little bit on what you meant by "restart CC0/CC1" ? May explain the ideal situation with all 4 PWMs on how it should work. 

Could you explain how you did it with the RTC in nRF52 series  ? 

It would be easier for me to describe it to R&D to get their advice if I have fully understood  your need.  

[LukeC]

Hung,

Thanks again for all of your time and effort on this.

1. NR52 Method

Dedicated RTC2 (RTC0 is BLE, RTC1 is app timer)

RTC2 - 2 CC channels used

RTC Channel0 - PWM Duty Factor 

RTC Channle1 - PWM base timer/reload

PPI - 3 channels

PPI Chan0 - RTC Channel0 Compare Event -> GPIOTE task set

PPI Chan1 - RTC Channel1 Compare Event -> GPIOTE task clr

PPI Chan2 - RTC Channel1 Compare Event -> RTC Task Clear

Functionality

PPI Chan0 sets the LED for the PWM.

PPI Chan1 clears the LED PWM for the base timer/reload

PPI Chan2 Clears the RTC count to restart the PWM/CC Channels

2. Issues implementing this in NRF54L15

There is one GRTC not multiple RTCs like in the NRF52. Therefore one cannot dedicate an RTC to this.  If the RTC Clear Task is called, this will reset the RTOS base timer correct?  And reset the logging timestamp?

I don't see another way to restart the CC channels on the GRTC in the NRF54L.  I can copy the above configuration in the NRF54 exactly, except PPI Chan2.

I am also not sure even if I use the NRF_GRTC_TASK_CLEAR task, if the GRTC CC channels will re-enable since they are one-shot in the GRTC.

[LukeC]

uint8_t ppi_ccchan0, ppi_chan1, ppi_chan2, ppi_chan2, ppi_chan3;

void ppi_init(void)
{
    nrfx_err_t nrfx_err;
    uint32_t event_address, task_address;

    // Set PWM PIN on RTC compare channel0 / Duty factor channel
    nrfx_err = nrfx_gppi_channel_alloc(&ppi_ccchan0);

    if (nrfx_err != NRFX_SUCCESS)
    {
        LOG_ERR("nrfx_gppi_channel_alloc failed.");
    }

    event_address = nrfx_grtc_event_compare_address_get(ccchan0.channel);
    task_address = nrfx_gpiote_set_task_address_get(&gpiote_inst, GPIOTE_PIN);
    nrfx_gppi_channel_endpoints_setup(ppi_ccchan0, event_address, task_address);
    nrfx_gppi_channels_enable(BIT(ppi_ccchan0));

    // Clear PWM PIN on RTC compare channel1 / pwm base timer
    nrfx_err = nrfx_gppi_channel_alloc(&ppi_chan1);

    if (nrfx_err != NRFX_SUCCESS)
    {
        LOG_ERR("nrfx_gppi_channel_alloc failed.");
    }

    event_address = nrfx_grtc_event_compare_address_get(ccchan1.channel);
    task_address = nrfx_gpiote_clr_task_address_get(&gpiote_inst, GPIOTE_PIN);
    nrfx_gppi_channel_endpoints_setup(ppi_chan1, event_address, task_address);

    nrfx_gppi_fork_endpoint_setup(ppi_chan1,
                                  nrfx_grtc_task_address_get(NRF_GRTC_TASK_CLEAR));

    nrfx_gppi_channels_enable(BIT(ppi_chan1));
}

here is an attempt to use the GRTC_TASK_CLEAR.  This still only sets the led once/clears the led once.