From 3027cead01d8aacce03dc360cedaa4cc44a062fc Mon Sep 17 00:00:00 2001
From: Solomon Peachy <pizza@shaftnet.org>
Date: Wed, 18 Nov 2020 14:08:17 -0500
Subject: hosted:  Improve buffer underrun handling in the ALSA driver

 * Bump internal mix buffer size by 4x, to 1K frames (matching ALSA period)
 * Handle an underrun that occurs when filling the audio buffer
 * Log underruns and make them available in the debug info

Change-Id: I28d56dd35d88851fa167ad92368a5882937a758f
---
 firmware/target/hosted/pcm-alsa.c | 65 +++++++++++++++++++++++++++++++--------
 1 file changed, 53 insertions(+), 12 deletions(-)

(limited to 'firmware/target/hosted/pcm-alsa.c')

diff --git a/firmware/target/hosted/pcm-alsa.c b/firmware/target/hosted/pcm-alsa.c
index 14e1c4cd3e..1854f67ba0 100644
--- a/firmware/target/hosted/pcm-alsa.c
+++ b/firmware/target/hosted/pcm-alsa.c
@@ -62,6 +62,12 @@
 #define DEFAULT_PLAYBACK_DEVICE "plughw:0,0"
 #define DEFAULT_CAPTURE_DEVICE "default"
 
+#if MIX_FRAME_SAMPLES < 512
+#error "MIX_FRAME_SAMPLES needs to be at least 512!"
+#elif MIX_FRAME_SAMPLES < 1024
+#warning "MIX_FRAME_SAMPLES <1024 may cause dropouts!"
+#endif
+
 static const snd_pcm_access_t access_ = SND_PCM_ACCESS_RW_INTERLEAVED; /* access mode */
 #if defined(SONY_NWZ_LINUX) || defined(HAVE_FIIO_LINUX_CODEC)
 /* Sony NWZ must use 32-bit per sample */
@@ -83,6 +89,8 @@ static sample_t *frames = NULL;
 static const void  *pcm_data = 0;
 static size_t       pcm_size = 0;
 
+static unsigned int xruns = 0;
+
 static snd_async_handler_t *ahandler = NULL;
 static pthread_mutex_t pcm_mtx;
 static char signal_stack[SIGSTKSZ];
@@ -117,17 +125,21 @@ static int set_hwparams(snd_pcm_t *handle)
     snd_pcm_hw_params_malloc(&params);
 
     /* Size playback buffers based on sample rate.
-       Note these are in FRAMES, and are sized to be about 10ms
-       for the buffer and 2.5ms for the period */
+
+       Buffer size must be at least 4x period size!
+
+       Note these are in FRAMES, and are sized to be about 8.5ms
+       for the buffer and 2.1ms for the period
+     */
     if (pcm_sampr > SAMPR_96) {
-        buffer_size = MIX_FRAME_SAMPLES * 16 * 4; /* 32k */
-        period_size = MIX_FRAME_SAMPLES * 4 * 4;  /*  4k */
+        buffer_size = MIX_FRAME_SAMPLES * 4 * 4;
+        period_size = MIX_FRAME_SAMPLES * 4;
     } else if (pcm_sampr > SAMPR_48) {
-        buffer_size = MIX_FRAME_SAMPLES * 16 * 2; /* 16k */
-        period_size = MIX_FRAME_SAMPLES * 4 * 2;  /*  2k */
+        buffer_size = MIX_FRAME_SAMPLES * 2 * 4;
+        period_size = MIX_FRAME_SAMPLES * 2;
     } else {
-        buffer_size = MIX_FRAME_SAMPLES * 16; /*  4k */
-        period_size = MIX_FRAME_SAMPLES * 4;  /*  1k */
+        buffer_size = MIX_FRAME_SAMPLES * 4;
+        period_size = MIX_FRAME_SAMPLES;
     }
 
     /* choose all parameters */
@@ -407,7 +419,8 @@ static void async_callback(snd_async_handler_t *ahandler)
 
     if (state == SND_PCM_STATE_XRUN)
     {
-        logf("underrun!");
+        xruns++;
+        logf("initial underrun!");
         err = snd_pcm_recover(handle, -EPIPE, 0);
         if (err < 0) {
             logf("XRUN Recovery error: %s", snd_strerror(err));
@@ -432,8 +445,20 @@ static void async_callback(snd_async_handler_t *ahandler)
         {
             if (copy_frames(false))
             {
+            retry:
                 err = snd_pcm_writei(handle, frames, period_size);
-                if (err < 0 && err != period_size && err != -EAGAIN)
+                if (err == -EPIPE)
+                {
+                    logf("mid underrun!");
+                    xruns++;
+                    err = snd_pcm_recover(handle, -EPIPE, 0);
+                    if (err < 0) {
+                       logf("XRUN Recovery error: %s", snd_strerror(err));
+                       goto abort;
+                    }
+                    goto retry;
+                }
+                else if (err != period_size)
                 {
                     logf("Write error: written %i expected %li", err, period_size);
                     break;
@@ -452,7 +477,18 @@ static void async_callback(snd_async_handler_t *ahandler)
         while (snd_pcm_avail_update(handle) >= period_size)
         {
             int err = snd_pcm_readi(handle, frames, period_size);
-            if (err < 0 && err != period_size && err != -EAGAIN)
+            if (err == -EPIPE)
+            {
+                logf("rec mid underrun!");
+                xruns++;
+                err = snd_pcm_recover(handle, -EPIPE, 0);
+                if (err < 0) {
+                   logf("XRUN Recovery error: %s", snd_strerror(err));
+                   goto abort;
+                }
+		continue;  /* buffer contents trashed, no sense in trying to copy */
+            }
+            else if (err != period_size)
             {
                 logf("Read error: read %i expected %li", err, period_size);
                 break;
@@ -751,11 +787,16 @@ void pcm_play_dma_postinit(void)
 #endif
 }
 
-int pcm_alsa_get_rate(void)
+unsigned int pcm_alsa_get_rate(void)
 {
     return real_sample_rate;
 }
 
+unsigned int pcm_alsa_get_xruns(void)
+{
+    return xruns;
+}
+
 #ifdef HAVE_RECORDING
 void pcm_rec_lock(void)
 {
-- 
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