[Bug] Clicks/pops with WM8960 I2S codec on PI4 and 5

[zanellia]

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How difficult would it be to have simultaneous read + write over I2S with DMA for the PI5 as it is implemented for the PI4? See, e.g., #545 . Is there any obvious starting point regarding the adaptation of the driver for the RP1 peripheral?

[rsta2]

Unfortunately I cannot remember well, why I did not support the DeviceModeTXRX. It's likely that it was only to reduce complexity and effort, because there was much to do, when the RPi 5 arrived. It doesn't look too difficult to add DeviceModeTXRX. I will work on this, which will take some days. There must be another DMA channel and DMA buffers added to the driver, so that TX and RX can work together.

[rsta2]

This was much less effort, than it was expected. The update is on the develop branch. I tested it with a WM8960 codec with master clock.

[zanellia]

@rsta2 thanks a lot! I should be able to test it tonight/tomorrow.

[rsta2]

You are welcome.

[zanellia]

Tested - it works perfectly, thanks again!

[zanellia]

I realized a couple of days ago that there are some periodic clicks/pops in the audio output even when running the stock version of sound-controller. The same code compiled for RPI4 doesn't have the same problem. I have been trying to debug this for quite some time, but still haven't found neither the solution nor the cause. Does anyone have any hint/idea?

[rsta2]

Is this in master or slave configuration of the I2S clock? Are the clicks/pops lout or relatively quiet?

[zanellia]

Relatively quiet. It's a single sample being held constant, 3 times every 560ms then 1.2s of silence and then the patterns repeats. I generated this signal with start sndi2s o m osc sine 10000.

Interestingly enough, I hear the same pattern using Raspbian OS + the WaveShare Audio Hat https://www.waveshare.com/wiki/WM8960_Audio_HAT

[rsta2]

The Circle I2S driver has been ported from Raspberry Pi OS. It will be difficult to find the reason for this problem. I don't even have the necessary tools to detect that this happens. 🙁

[zanellia]

On which driver for which physical board in particular is Circle's I2S driver based on? I can try to open an issue on the Raspberry OS repo.

In order to detect you can either listen to the output when emitting a high-frequency sinusoid using 'osc', or record the same output into any DAW (I use Reaper) and look at the spectrogram.

By the way, is it possible to use I2S in slave mode? I.e., 'start sndi2s io s'?

[rsta2]

The Linux I2S driver is independent of the actual board used. So if you want to report this issue, I would do it for the Waveshare board, with which you have noticed the problem. I2S might work in slave mode, but I have no hardware to test this.

[zanellia]

For reference, the same problem was originally observed with Circle on RPI5 with the SparkFun WM8960 breakout https://www.sparkfun.com/sparkfun-audio-codec-breakout-wm8960.html.

[zanellia]

I made a couple of small changes to the driver in order to configure the codec as master, tested it on the SparkFun breakout and the pops are gone - I can make a PR if that's useful.