alsa-project/alsa-lib issue #261 was opened from sprudent: Hello erveryone, I am getting random channel swap when using speaker test to output sequencially a pink noise on every channel of the soundcard. I tested two distinct usb soundcard getting the same issue. I could identify a suspicious log showing at the same time the channels swapped. Tested and reproduced on a recent archlinux image (see system information). ``` [Aug16 18:26] xhci_hcd 0000:00:14.0: ERROR Transfer event TRB DMA ptr not part of current TD ep_index 11 comp_code 1 [ +0.000134] xhci_hcd 0000:00:14.0: Looking for event-dma 0000000014ed98e0 trb-start 0000000014ed98f0 trb-end 0000000014ed98f0 seg-start 0000000014ed9000 seg-end 0000000014ed9ff0 ``` ### system information ``` uname -r 5.18.7-arch1-1 ``` ``` aplay -l **** List of PLAYBACK Hardware Devices **** card 0: Audio [Intel HDMI/DP LPE Audio], device 0: HdmiLpeAudio [Intel HDMI/DP LPE Audi] Subdevices: 1/1 Subdevice #0: subdevice #0 card 0: Audio [Intel HDMI/DP LPE Audio], device 1: HdmiLpeAudio [Intel HDMI/DP LPE Audi] Subdevices: 1/1 Subdevice #0: subdevice #0 card 0: Audio [Intel HDMI/DP LPE Audio], device 2: HdmiLpeAudio [Intel HDMI/DP LPE Audi] Subdevices: 1/1 Subdevice #0: subdevice #0 card 1: ICUSBAUDIO7D [ICUSBAUDIO7D], device 0: USB Audio [USB Audio] Subdevices: 1/1 Subdevice #0: subdevice #0 card 2: bytchtes8316 [bytcht-es8316], device 0: Audio (*) [] Subdevices: 1/1 Subdevice #0: subdevice #0 card 2: bytchtes8316 [bytcht-es8316], device 1: Deep-Buffer Audio (*) [] Subdevices: 1/1 Subdevice #0: subdevice #0 ``` [alsa-info.txt](https://github.com/alsa-project/alsa-lib/files/9358483/alsa-info.txt) ### Test with dmix #### Description First test was made with alsa dmix plugin. Multiple processes running in parrallel and outputing to dmix pcm device. #### Alsa configuration ``` pcm.play_8 { @args [ CARD ] @args.CARD { type string } type dmix ipc_key 5678 slave { pcm $CARD channels 8 period_time 0 period_size 1024 buffer_size 4096 rate 44100 } bindings { 0 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 } } ``` #### Step to reproduce Run this script to simulate multiple processes writing to dmix device at the same time ``` for i in $(seq 20) do speaker-test -r44100 -D"play_8:\"hw:1\"" -c8 -t pink & done ``` Then on another tty, start a speaker-test command outputing a sine wave in order to identify channel mapping by correlating speaker test output with audio output. `speaker-test -r44100 -D"play_8:\"hw:1\"" -c8 -t sine` ``` 0 - Front Left 4 - Front Center 1 - Front Right 3 - Side Right 7 - Side Right 2 - Side Left 6 - Side Left 5 - LFE Time per period = 21.998519 ... ``` #### Expected result Audio output to the same channels during all the test #### Actual result Random audio channel swap correlated with dmesg log mentioned above. ### Second test with direct output #### Alsa configuration No specific configuration required #### Step to reproduce Run speaker-following test command and wait for channel swap `speaker-test -r44100 -Dsurround71:ICUSBAUDIO7D -c8` #### Expected result Audio output to the same channels during all the test #### Actual result Random audio channel swap correlated with dmesg log mentioned above. The chanel swap happen far less often than with dmix. ### Interpretation The DMA transfer ring buffer get messed up after a while (see dmesg log) and interleaved audio frames get shifted in soundcard buffer. If I unplug/replug usb soundcard and try again, channel mapping goes back to the correct order. My alsa, kernel and usb driver knowledge is limited, so I come to you for a little help. Tell me if you need more information to reproduce. Thank's, Sylvain Issue URL : https://github.com/alsa-project/alsa-lib/issues/261 Repository URL: https://github.com/alsa-project/alsa-lib
