Single SPI transfer from PPI

RE: Single SPI transfer from PPI

Nick_RA — Tue, 28 Apr 2020 16:28:36 GMT

You're right, I was getting an error. I was setting the PPI channel by NRF_PPI->CHENSET |= (1 << ppi_cs_low) but using the driver to disable it (it was a quick test and late in the day!) which was returning unallocated channel errors.

The good news is it works by enabling / disabling PPI so I can happily play 44.1kHz audio from a WAV file which is pretty impressive 🙂 The bad news is it won't work with BLE but that's probably because my PPI is upsetting the Softdevice - tomorrow's job is to rewrite the PPI stuff properly using the drivers.

Thanks

Nick

RE: Single SPI transfer from PPI

Jørgen Holmefjord — Mon, 27 Apr 2020 19:07:03 GMT

How did you assign/enable the PPI channels? The functions should return an error code if the call is not successful, did you check that?

RE: Single SPI transfer from PPI

Nick_RA — Mon, 27 Apr 2020 18:05:30 GMT

OK thanks, I'll have to re-evaluate how I approach this then.

Is there any reason why disabling the PPI channel didn't work?

RE: Single SPI transfer from PPI

Jørgen Holmefjord — Mon, 27 Apr 2020 17:39:04 GMT

nrfx_spim_xfer() will only setup the buffers for you when you add the HOLD_XFER flag. There is nothing in the peripheral that clears the buffer pointers whenever the transfer is completed. If you want to stop transferring data when the ring buffer is empty, you need to stop the timer

RE: Single SPI transfer from PPI

Nick_RA — Mon, 27 Apr 2020 14:41:21 GMT

Sorry for not being clear. At the moment for testing no I'm not updating dac_buf, I'm just doing the one-off xfer as part of main().

In the real world, I'll be feeding data into a ring buffer, and taking them out 2 bytes at a time based on the timer event. So I'll need the SPI to be transmitting when there is data and idle when the data has finished. Right now the SPI transmits all the time from the PPI.

I could mess around with starting/stopping the timer or disabling the PPI event although I was hoping that the xfer would be a one-shot so I wouldn't have to.

Hope that makes it clearer...

Regards

Nick

Edit: I also added a spi event handler and included a couple of lines to disable the PPI channels but that didn't work

    nrfx_ppi_channel_disable(ppi_cs_low);
    nrfx_ppi_channel_disable(ppi_spi_start);
    nrfx_ppi_channel_disable(ppi_cs_hi);

RE: Single SPI transfer from PPI

Jørgen Holmefjord — Mon, 27 Apr 2020 13:14:20 GMT

Hi,

I'm not sure I understand your question. Do you update the dac_buf somewhere, since you did not expect the same two bytes being sent every timer event?

Best regards,
Jørgen