channel group function nrfx_gppi_group_alloc() not available on nRF54L15

[Daniel Chisholm]

I had been doing this:

    nrfx_dppi_t dppi20 = NRFX_DPPI_INSTANCE(20);
    rc = nrfx_dppi_channel_alloc(&dppi20,&dppi_ch_2);
	rc = nrfx_dppi_group_alloc(&dppi20,&chg_2);
    NRF_DPPIC20->CHG[chg_2] = BIT(dppi_ch_2);

    NRF_GPIOTE20->PUBLISH_IN[channel_in_2] = dppi_ch_2 | 0x80000000;
    NRF_EGU20->SUBSCRIBE_TRIGGER[2] = dppi_ch_2 | 0x80000000;
    NRF_TIMER20->SUBSCRIBE_CAPTURE[2] = dppi_ch_2 | 0x80000000;
    NRF_DPPIC20->SUBSCRIBE_CHG[chg_2].DIS = dppi_ch_2 | 0x80000000;

    NRF_DPPIC20->TASKS_CHG[chg_2].EN = 1; // enable

What it does:

• create a CHG (channel group)
• DPPI is triggered by a GPIOTE in-event
• DPPI then triggers and EGU, a TIMER capture, and...
• DPPI also triggers its own CHG.DIS task (i.e. disables further captures)

But I now need to do this with gppi, in order connect a DPPI across domains... I want to have a GPIOTE30->EVENTS.IN[] trigger a TIMER20->TASKS.CAPTURE[]

So I take a deep breath, then #include <helpers/nrfx_gppi.h> and read the documentation, such as it is:

• the file ncs/v2.9.0/modules/hal/nordic/nrfx/helpers/nrfx_gppi.h
• and the online "and the Nordic online docs "nrfx: Generic PPI layer"

Oh, so it seems easy... there is a "nrfx_gppi_group_alloc()" function just like you'd expect.  Let's code it up and compile it:

    rc = nrfx_gppi_channel_alloc(&gppi_ch_2);
    nrfx_gppi_channels_enable(BIT(gppi_ch_2));
    static nrfx_gppi_channel_group_t g_chg_2;
	rc = nrfx_gppi_group_alloc(&g_chg_2);
    // NRF_DPPIC20->CHG[chg_2] = BIT(dppi_ch_2);
    nrfx_gppi_channels_include_in_group(BIT(gppi_ch_2),g_chg_2);

But no, it isn't easy!

While nrfx_gppi_group_alloc() and nrfx_gppi_channels_include_in_group() are nicely defined in helpers/nrfx_gppi.h.... they are not IMPLEMENTED in the file nrfx/helpers/nrfx_gppi_dppi_ppib_lumos.c (where nrfx_gppi_channel_alloc() etc are implemented).

/(....c.obj): in function `l15timings_init':
/(......).c:940: undefined reference to `nrfx_gppi_group_alloc'
/(...).c:948: undefined reference to `nrfx_gppi_channels_include_in_group'
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

So my question is.... how am I supposed to use channel groups, using the GPPI system?

[Einar Thorsrud]

Hi,

Currently, I think the only driver option is using the nrfx_dppi_* API. You can see an example of that in the ESB implementation, here.

[Daniel Chisholm]

Thanks Einar.  In which case, I think that in order to use channel groups when using the gppi library, one of these would be needed:

• to add implementations of nrfx_gppi_group_alloc() and nrfx_gppi_channels_include_in_group() to nrfx_gppi_dppi_ppib_lumos.c
  • I would guess that this "simple feature request" might actually be a pretty big job (and perhaps explains why it isn't already done)
  • FYI I am pretty impressed with the implementation of nrfx_gppi_dppi_ppib_lumos.c and how it automagically handles the allocation of PPIBxy resources and their interconnection; if you have the chance, please pass on my compliments to the designers
• or, to add a "get_DPPIs" functions to the GPPI library, to expose the internal GPPI-allocated DPPI channel numbers
  • this would allow GPPI to be used for what it is good at (cleanly bridging DPPI across different domains)
  • by returning an array of DPPICxy and the DPPI channel number allocated by GPPI for each of them, my program could then implement channel groups at the DPPIC level