[alsa-devel] [PATCH 2/3] ALSA: usb-audio: M-Audio FT C400 skip packet quirk
eldad at fogrefinery.com
Sun Jan 13 23:02:03 CET 2013
Attain constant real-world latency by skipping 16 data packets.
The number of packets to be skipped was found by trial and error.
Signed-off-by: Eldad Zack <eldad at fogrefinery.com>
sound/usb/quirks.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
index acc12f0..ace0210 100644
@@ -859,6 +859,17 @@ void snd_usb_endpoint_start_quirk(struct snd_usb_endpoint *ep)
if ((le16_to_cpu(ep->chip->dev->descriptor.idVendor) == 0x23ba) &&
ep->type == SND_USB_ENDPOINT_TYPE_SYNC)
ep->skip_packets = 4;
+ * M-Audio Fast Track C400 - when packets are not skipped, real world
+ * latency varies by approx. +/- 50 frames (at 96KHz) each time the
+ * stream is (re)started. When skipping packets 16 at endpoint start
+ * up, the real world latency is stable within +/- 1 frame (also
+ * across power cycles).
+ if (ep->chip->usb_id == USB_ID(0x0763, 0x2030) &&
+ ep->type == SND_USB_ENDPOINT_TYPE_DATA)
+ ep->skip_packets = 16;
void snd_usb_ctl_msg_quirk(struct usb_device *dev, unsigned int pipe,
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