Hi,
I have a program that configures a Behringer UMC404HD 192k USB audio
interface for playback as follows (pseudocode):
snd_pcm_hw_params_set_channels(pcm, hwp, 2);
snd_pcm_hw_params_set_format(pcm, hwp, SND_PCM_FORMAT_S24_3LE);
snd_pcm_hw_params_set_access(pcm, hwp, SND_PCM_ACCESS_MMAP_INTERLEAVED);
snd_pcm_hw_params_set_rate(pcm, hwp, val=96000, dir=0);
snd_pcm_hw_params_set_period_size_near(pcm, hwp, val=513, dir=0);
// If I confirm at this point with snd_pcm_hw_params_get_period_size,
// I get back 513.
snd_pcm_hw_params_set_buffer_size_near(pcm, hwp, val=2052);
snd_pcm_hw_params(pcm, hwp);
// If I confirm with snd_pcm_hw_params_get_buffer_size,
// I get back 2052.
On Linux 5.10.94 (specifically Arch Linux ARM package
linux-rpi-5.10.94-1), this succeeds, and I can play back audio just
fine. On 5.15.21 (specifically linux-rpi-5.15.21-3), all the calls
succeed apart from the last one, which returns EINVAL.
(My actual program is written in Rust and uses a Rust wrapper library
for libasound, https://docs.rs/alsa/0.6.0/alsa/, but the calls should be
the ones listed.)
I confirmed with snd_pcm_hw_params_test_format that the S24_3LE format
is supported. On both kernels it is successful. I confirmed with
snd_pcm_hw_params_test_rate that 96 kHz is supported. On both kernels it
is successful. There are differences though. When I query these:
snd_pcm_hw_params_get_period_size_min
snd_pcm_hw_params_get_period_size_max
snd_pcm_hw_params_get_buffer_size_min
snd_pcm_hw_params_get_buffer_size_max
Then on 5.10.94 (the good version), I get:
period size min/max: 12/32768, buffer size min/max: 24/65536
But on 5.15.21 (the bad version), I get:
period size min/max: 13/71332, buffer size min/max: 26/142663
Also, after I set the period size to 513, if I then query the buffer
size min/max, on 5.10.94 I get:
buffer size min/max: 1026/65536
But on 5.15.21 I get:
buffer size min/max: 1027/142663
In lsmod, snd_usb_audio shows up, and from lsusb -v, the UMC404HD
appears to be a standard USB audio interface. The lsusb output is
identical on both kernels.
Please let me know if there is anything I can do to help further
diagnose the issue, or if I should report this elsewhere.
Kind regards,
Ruud van Asseldonk
