Dne 31. 01. 24 v 9:48 Pavel Hofman napsal(a):
Hi,
Users of RPi's hdmi:vc4-hdmi report random channel swapping after an
xrun. Tested (among other clients) on speaker-test, details
https://forums.raspberrypi.com/viewtopic.php?p=2187582#p2187540
Experienced RPi developer has diagnosed the driver - HDMI device and DMA
are correctly reset at xrun recovery (i.e. snd_pcm_stop(XRUN) in the
driver -> snd_pcm_prepare in the client).
Therefore an option is that alsa supplies misaligned 8ch samples after
the xrun recovery.
Users checked the older HDMI driver bcm2835_audio (bcm2835-pcm.c) which
accepts standard S16/24_LE formats and does not require the iec958
plugin and xruns did not cause any channel swaps.
Hence aiming at the iec958 plugin. It seems to keep state (e.g.
iec->counter) which perhaps may not be reset at snd_pcm_prepare.
Hm, iec->counter seems to be reset correctly at prepare through
plugin->prepare -> snd_pcm_plugin_call_init_cb -> snd_pcm_iec958_init .
It should mark the audio block with 'Z' on the first byte of the
recovered stream OK. Could perhaps be any cached samples within the
chain, not cleared by prepare? But that would cause issues in other
cases too... So I have no idea now :-)
