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@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 --- a/sound/usb/quirks.c +++ b/sound/usb/quirks.c @@ -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,