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| author | Clemens Ladisch <clemens@ladisch.de> | 2006-01-12 08:17:49 +0100 |
|---|---|---|
| committer | Jaroslav Kysela <perex@suse.cz> | 2006-01-22 16:24:09 +0100 |
| commit | 4b2849283461a64c6d8cc6c7e72c62d7b4d91b43 (patch) | |
| tree | fc3b053257c89bc1afd2796ef29411fc5cad2d90 /sound | |
| parent | 54c63cfc153c6909a5d5dbe6072e8704b091f30e (diff) | |
| download | linux-3.10-4b2849283461a64c6d8cc6c7e72c62d7b4d91b43.tar.gz linux-3.10-4b2849283461a64c6d8cc6c7e72c62d7b4d91b43.tar.bz2 linux-3.10-4b2849283461a64c6d8cc6c7e72c62d7b4d91b43.zip | |
[ALSA] usb-audio: don't use empty packets at start of playback
Modules: USB generic driver
Some widespread USB interface chips with adaptive iso endpoints hang
after receiving a series of empty packets when they expect data (ALSA
bug#1585). To avoid this, we have to send packets containing silence
(zero samples) instead.
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Diffstat (limited to 'sound')
| -rw-r--r-- | sound/usb/usbaudio.c | 26 |
1 files changed, 21 insertions, 5 deletions
diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c index a1bd8040dea..95729730bcd 100644 --- a/sound/usb/usbaudio.c +++ b/sound/usb/usbaudio.c @@ -478,22 +478,38 @@ static int retire_playback_sync_urb_hs(struct snd_usb_substream *subs, /* * Prepare urb for streaming before playback starts. * - * We don't care about (or have) any data, so we just send a transfer delimiter. + * We don't yet have data, so we send a frame of silence. */ static int prepare_startup_playback_urb(struct snd_usb_substream *subs, struct snd_pcm_runtime *runtime, struct urb *urb) { - unsigned int i; + unsigned int i, offs, counts; struct snd_urb_ctx *ctx = urb->context; + int stride = runtime->frame_bits >> 3; + offs = 0; urb->dev = ctx->subs->dev; urb->number_of_packets = subs->packs_per_ms; for (i = 0; i < subs->packs_per_ms; ++i) { - urb->iso_frame_desc[i].offset = 0; - urb->iso_frame_desc[i].length = 0; + /* calculate the size of a packet */ + if (subs->fill_max) + counts = subs->maxframesize; /* fixed */ + else { + subs->phase = (subs->phase & 0xffff) + + (subs->freqm << subs->datainterval); + counts = subs->phase >> 16; + if (counts > subs->maxframesize) + counts = subs->maxframesize; + } + urb->iso_frame_desc[i].offset = offs * stride; + urb->iso_frame_desc[i].length = counts * stride; + offs += counts; } - urb->transfer_buffer_length = 0; + urb->transfer_buffer_length = offs * stride; + memset(urb->transfer_buffer, + subs->cur_audiofmt->format == SNDRV_PCM_FORMAT_U8 ? 0x80 : 0, + offs * stride); return 0; } |