🐛 [BUG] No sound via Adafruit I2S Audio Bonnet (UDA1334A)

[htamas2]

Hardware and software

• mt32-pi version: v0.11.0, also tried with v0.11.0-4-g07004ea (git head)
• Raspberry Pi model: Raspberry Pi Zero 2 W
• HATs: Adafruit I2S Audio Bonnet (UDA1334A)
• USB devices: Novation Launchpad X
• MIDI host: None

Bug description

If I set output_device to hdmi, everything works: I can play on a usb midi keyboard or via rtp-midi, using either fluidsynth or munt. However, if I set output_device to i2s, there is no sound output.

The same configuration is supported by Circle out of the box. It works flawlessly in circle/sample/29-miniorgan or in minisynth. If I write a minimal kernel with a class that extends CI2SSoundBaseDevice and overrides GetChunk(u32*, unsigned) to output a square wave, I can hear the sound. Incidentally it also works in Raspbian.

Steps to reproduce

1. Install mt32-pi v0.11.0 to a fresh sd card (or build from git HEAD)
2. Update mt32-pi.cfg with output_device = i2s, default_synth = soundfont
3. Boot the pi from the sd card
4. Play notes on the midi keyboard, hear nothing

Expected behavior

There should be sound.

Configuration file (changes from default)

[system]
verbose = on
default_synth = soundfont

[audio]
output_device = i2s

[network]
mode = wifi
ftp = on
ftp_password = ********

Additional information

In CMT32Pi::AudioTask(), IntBuffer still contains valid sample data which is then sent to CSoundBaseDevice::Write(const void *, size_t). Compare this to the working Circle demo code that doesn't call CSoundBaseDevice::Write but overrides CI2SSoundBaseDevice::GetChunk to fill the buffer on an IRQ. I wonder if that makes any difference or is just a consequence of mt32-pi being multithreaded.

[dwhinham]

The GetChunk() versus Write() stuff shouldn't affect anything at all, it just determines when the audio data is passed to the driver (interrupt context versus not). Munt/Fluid's rendering is too intensive to run inside an interrupt without wrecking performance/timing of other tasks, hence why GetChunk() is not used.

I have other UDA1334A DACs that are working fine here, so there's not much to suggest other than:

• Try other sample rates. 48000 is the mt32-pi default, but Adafruit are using 44100 in their setup guide, miniorgan is using 192000. I have some DACs that flat-out refuse to work at certain rates, so experiment with that. You may have to increase chunk size to prevent underruns at higher rates.
• This DAC has a mute feature on Pin 16. This should not conflict with anything, but you could check to see if it is being driven to muted state (whatever that may be, high or low, not sure).

[htamas2]

Thanks for the quick reply. You are right, the mute pin was the culprit. When probing for the Pisound in CMT32Pi::Initialize, pin 16 (used for Pisound's oversampling ratio) is driven low which mutes the sound.

[dwhinham]

Thankyou for testing, and great catch with the Pisound probing - I'd forgotten about this device.

I've attempted a fix, which you can test by grabbing the kernels package from this build run and just replacing the kernels: https://github.com/dwhinham/mt32-pi/actions/runs/1723643561

I've basically just added a destructor to the Pisound driver so that when it's deleted, the affected GPIO pins are reset back to being inputs in pull-down mode (as they should be on power-on, according to Broadcom docs).

If you can test this when you get a chance I'll merge it for the next release.

Thanks!

[htamas2]

I can confirm it works great. Thank you.

[dwhinham]

Excellent, thanks for the quick test and again for the report. This will probably improve compatibility with some other DAC accessories that have a mute pin too.

This fix is now on the develop branch and will be part of the next release.