At present, applications can change avail_min parameter of PCM substream by two ways; via mapped control data, and by executing ioctl(2) with SNDRV_PCM_IOCTL_SYNC_PTR. The former is available in a case that the applications map the data successfully.
When utilizing alsa-lib API, the above is done by a call of 'snd_pcm_sw_params()' to hw PCM plugin. In current implementation, this call has an sub-effect to issue appl_ptr unexpectedly.
This commit adds a helper function to issue avail_min without the sub-effect.
Signed-off-by: Takashi Sakamoto o-takashi@sakamocchi.jp --- src/pcm/pcm_hw.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/src/pcm/pcm_hw.c b/src/pcm/pcm_hw.c index aacfa669..c8fef64d 100644 --- a/src/pcm/pcm_hw.c +++ b/src/pcm/pcm_hw.c @@ -151,6 +151,15 @@ static int sync_ptr(snd_pcm_hw_t *hw, unsigned int flags) return 0; }
+static int issue_avail_min(snd_pcm_hw_t *hw) +{ + if (!hw->mmap_control_fallbacked) + return 0; + + /* Avoid unexpected change of applptr in kernel space. */ + return sync_ptr1(hw, SNDRV_PCM_SYNC_PTR_APPL); +} + static int issue_applptr(snd_pcm_hw_t *hw) { if (!hw->mmap_control_fallbacked) @@ -492,7 +501,7 @@ static int snd_pcm_hw_sw_params(snd_pcm_t *pcm, snd_pcm_sw_params_t * params) params->silence_size == pcm->silence_size && old_period_event == hw->period_event) { hw->mmap_control->avail_min = params->avail_min; - return sync_ptr(hw, 0); + return issue_avail_min(hw); } if (params->tstamp_type == SND_PCM_TSTAMP_TYPE_MONOTONIC_RAW && hw->version < SNDRV_PROTOCOL_VERSION(2, 0, 12)) {