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Range check the jitter values to avoid bogus sample rate adjustments.

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The expected deviation should not be more than 1Hz per second. The USB
v2.0 specification also mandates this requirement. Refer to chapter
5.12.4.2 about feedback.

PR:		208791
MFC after:	3 days
This commit is contained in:
Hans Petter Selasky 2016-11-08 08:09:48 +00:00
parent cbd6713146
commit dd3dde9828
1 changed files with 16 additions and 3 deletions
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19
sys/dev/sound/usb/uaudio.c
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@ -2078,9 +2078,22 @@ uaudio_chan_play_sync_callback(struct usb_xfer *xfer, usb_error_t error)
* Use feedback value as fallback when there is no
* recording channel:
*/
if (ch->priv_sc->sc_rec_chan.num_alt == 0)
ch->jitter_curr = temp - sample_rate;
if (ch->priv_sc->sc_rec_chan.num_alt == 0) {
/*
* Range check the jitter values to avoid
* bogus sample rate adjustments. The expected
* deviation should not be more than 1Hz per
* second. The USB v2.0 specification also
* mandates this requirement. Refer to chapter
* 5.12.4.2 about feedback.
*/
if (temp > sample_rate)
ch->jitter_curr = 1;
else if (temp < sample_rate)
ch->jitter_curr = -1;
else
ch->jitter_curr = 0;
}
ch->feedback_rate = temp;
break;