Em Thu, 9 Jan 2014 09:29:57 -0200 Mauro Carvalho Chehab <m.chehab@xxxxxxxxxxx> escreveu: > Em Thu, 09 Jan 2014 09:17:13 +0100 > Clemens Ladisch <clemens@xxxxxxxxxx> escreveu: > > > Mauro Carvalho Chehab wrote: > > > I'm getting an weird behavior with em28xx, especially when the device > > > is connected into an audio port. > > > > > > http://git.linuxtv.org/mchehab/experimental.git/blob/refs/heads/em28xx-v4l2-v6:/drivers/media/usb/em28xx/em28xx-audio.c > > > > > > What happens is that, when I require xawtv3 to use any latency lower > > > than 65 ms, the audio doesn't work, as it gets lots of underruns per > > > second. > > > > The driver uses five URBs with 64 frames each, so of course it > > will not be able to properly handle periods smaller than that. > > > > > FYI, em28xx works at a 48000 KHz sampling rate, and its PM capture Hw > > > is described as: > > > > > > static struct snd_pcm_hardware snd_em28xx_hw_capture = { > > > .info = SNDRV_PCM_INFO_BLOCK_TRANSFER | > > > SNDRV_PCM_INFO_MMAP | > > > SNDRV_PCM_INFO_INTERLEAVED | > > > SNDRV_PCM_INFO_BATCH | > > > SNDRV_PCM_INFO_MMAP_VALID, > > > > > > .formats = SNDRV_PCM_FMTBIT_S16_LE, > > > > > > .rates = SNDRV_PCM_RATE_CONTINUOUS | SNDRV_PCM_RATE_KNOT, > > > > This should be just SNDRV_PCM_RATE_48000. > > Ok. > > > > > > .period_bytes_min = 64, /* 12544/2, */ > > > > This is wrong (if the driver doesn't install other constraints on the > > period length, like the USB audio class driver does). > > Ok, how should it be estimated? Those values here were simply glued from > the USB audio class driver a long time ago without a further analysis. > > I changed it to 188 (the minimum URB size I experimentally noticed with > the current settings) and it is now working fine with both xHCI and EHCI. PS.: using 188 there, the URBs now have a total actual size of 24 bytes. Regards, -- Cheers, Mauro -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
