New subject: [alsa-devel] [PATCH 4/6] alsa-lib:pcm: fix the hw_ptr update until the boundary available.

30 Dec 2016

From: mahendran.k mahendran.kuppusamy@in.bosch.com
For long time test case, the slave_hw_ptr will exceed the boundary
and wraparound the slave_hw_ptr. This slave boundary wraparound will
cause the rate->hw_ptr to wraparound irrespective of the rate->boundary
availability and due to that the available size goes wrong.
Hence, To get the correct available size,
- Its necessary to increment the rate->hw_ptr upto the rate->boundary
and then wraparound the rate->hw_ptr.
- While handling fraction part of slave period, rounded value will be
introduced by input_frames(). To eliminate rounding issue on rate->hw_ptr,
subtract last rounded value from rate->hw_ptr and add new rounded value
of present slave_hw_ptr fraction part to rate->hw_ptr.
Signed-off-by: mahendran.k mahendran.kuppusamy@in.bosch.com
Signed-off-by: Mounesh Sutar mounesh_sutar@mentor.com

diff --git a/src/pcm/pcm_rate.c b/src/pcm/pcm_rate.c
index 1f830dd..5bee77c 100644
--- a/src/pcm/pcm_rate.c
+++ b/src/pcm/pcm_rate.c
@@ -50,7 +50,7 @@ typedef struct _snd_pcm_rate snd_pcm_rate_t;
struct _snd_pcm_rate {
    snd_pcm_generic_t gen;
-	snd_pcm_uframes_t appl_ptr, hw_ptr;
+	snd_pcm_uframes_t appl_ptr, hw_ptr, last_slave_hw_ptr;
    snd_pcm_uframes_t last_commit_ptr;
    snd_pcm_uframes_t orig_avail_min;
    snd_pcm_sw_params_t sw_params;
@@ -563,14 +563,28 @@ static inline void snd_pcm_rate_sync_hwptr0(snd_pcm_t *pcm, snd_pcm_uframes_t sl
 {
    snd_pcm_rate_t *rate = pcm->private_data;
+	snd_pcm_sframes_t slave_hw_ptr_diff = slave_hw_ptr - rate->last_slave_hw_ptr;
+	snd_pcm_sframes_t last_slave_hw_ptr_frac;
+
    if (pcm->stream != SND_PCM_STREAM_PLAYBACK)
    	return;
-	/* FIXME: boundary overlap of slave hw_ptr isn't evaluated here!
-	 *        e.g. if slave rate is small... 
-	 */
-	rate->hw_ptr =
-		(slave_hw_ptr / rate->gen.slave->period_size) * pcm->period_size +
-		rate->ops.input_frames(rate->obj, slave_hw_ptr % rate->gen.slave->period_size);
+
+	if (slave_hw_ptr_diff < 0)
+		slave_hw_ptr_diff += rate->gen.slave->boundary; /* slave boundary wraparound */
+	else if (slave_hw_ptr_diff == 0)
+		return;
+	last_slave_hw_ptr_frac = rate->last_slave_hw_ptr % rate->gen.slave->period_size;
+	/* While handling fraction part fo slave period, rounded value will be introduced by input_frames().
+	 * To eliminate rounding issue on rate->hw_ptr, subtract last rounded value from rate->hw_ptr and
+	 * add new rounded value of present slave_hw_ptr fraction part to rate->hw_ptr. Hence,
+	 * rate->hw_ptr += [ (no. of updated slave periods * pcm rate period size) -
+	 * 				fractional part of last_slave_hw_ptr rounded value +
+	 * 				fractional part of updated slave hw ptr's rounded value ] */
+	rate->hw_ptr += (
+			(((last_slave_hw_ptr_frac + slave_hw_ptr_diff) / rate->gen.slave->period_size) * pcm->period_size) -
+			rate->ops.input_frames(rate->obj, last_slave_hw_ptr_frac) +
+			rate->ops.input_frames(rate->obj, (last_slave_hw_ptr_frac + slave_hw_ptr_diff) % rate->gen.slave->period_size));
+	rate->last_slave_hw_ptr = slave_hw_ptr;
rate->hw_ptr %= pcm->boundary;
 }
@@ -635,6 +649,7 @@ static int snd_pcm_rate_prepare(snd_pcm_t *pcm)
    	return err;
    *pcm->hw.ptr = 0;
    *pcm->appl.ptr = 0;
+	rate->last_slave_hw_ptr = 0;
    err = snd_pcm_rate_init(pcm);
    if (err < 0)
    	return err;
@@ -650,6 +665,7 @@ static int snd_pcm_rate_reset(snd_pcm_t *pcm)
    	return err;
    *pcm->hw.ptr = 0;
    *pcm->appl.ptr = 0;
+	rate->last_slave_hw_ptr = 0;
    err = snd_pcm_rate_init(pcm);
    if (err < 0)
    	return err;
-- 
1.7.9.5


    