diff options
| -rw-r--r-- | sound/firewire/amdtp-stream.c | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/sound/firewire/amdtp-stream.c b/sound/firewire/amdtp-stream.c index 8a7818130382..7486eec4d958 100644 --- a/sound/firewire/amdtp-stream.c +++ b/sound/firewire/amdtp-stream.c @@ -213,9 +213,21 @@ int amdtp_stream_add_pcm_hw_constraints(struct amdtp_stream *s, maximum_usec_per_period = USEC_PER_SEC * PAGE_SIZE / CYCLES_PER_SECOND / ctx_header_size; + // In IEC 61883-6, one isoc packet can transfer events up to the value + // of syt interval. This comes from the interval of isoc cycle. As 1394 + // OHCI controller can generate hardware IRQ per isoc packet, the + // interval is 125 usec. + // However, there are two ways of transmission in IEC 61883-6; blocking + // and non-blocking modes. In blocking mode, the sequence of isoc packet + // includes 'empty' or 'NODATA' packets which include no event. In + // non-blocking mode, the number of events per packet is variable up to + // the syt interval. + // Due to the above protocol design, the minimum PCM frames per + // interrupt should be double of the value of syt interval, thus it is + // 250 usec. err = snd_pcm_hw_constraint_minmax(runtime, SNDRV_PCM_HW_PARAM_PERIOD_TIME, - 5000, maximum_usec_per_period); + 250, maximum_usec_per_period); if (err < 0) goto end; |