PCM: Major simplification of the sub-sampling design. Now need no extra buffers because sub-sampling is done in place

1 files changed, 92 insertions, 551 deletions

diff --git a/nuttx/audio/pcm_decode.c b/nuttx/audio/pcm_decode.c
index f1ba4904d..0c0191dee 100644
--- a/nuttx/audio/pcm_decode.c
+++ b/nuttx/audio/pcm_decode.c
@@ -124,18 +124,8 @@ struct pcm_decode_s
   /* Fast forward support */
 
   uint8_t  subsample;              /* Fast forward rate: See AUDIO_SUBSAMPLE_* defns */
-  uint8_t  skip;                   /* Number of samples to be skipped */
+  uint8_t  skip;                   /* Number of sample bytes to be skipped */
   uint8_t  npartial;               /* Size of the partially copied sample */
-
-  /* REVISIT: I think we could get rid of all of this special buffer
-   * processing.  It seems like we should be able to do the sub-sampling
-   * in place without any additional buffers.
-   */
-
-  struct audio_buf_desc_s bufdesc; /* Allocated buffer description */
-  FAR struct ap_buffer_s *ffwd;    /* Audio buffer being subsampled into */
-  FAR struct ap_buffer_s *next;    /* Next available, empty audio buffer */
-  FAR struct ap_buffer_s *apb;     /* Allocated audio buffer */
 #endif
 };
 
@@ -161,29 +151,11 @@ static uint16_t pcm_leuint32(uint32_t value);
 
 static inline bool pcm_validwav(FAR const struct wav_header_s *wav);
 static bool pcm_parsewav(FAR struct pcm_decode_s *priv, uint8_t *data);
-#ifdef CONFIG_AUDIO_MULTI_SESSION
-static void pcm_upper_callback(FAR struct pcm_decode_s *priv,
-              uint16_t reason, FAR struct ap_buffer_s *apb,
-              uint16_t status, FAR void *session);
-#else
-static void pcm_upper_callback(FAR struct pcm_decode_s *priv,
-              uint16_t reason, FAR struct ap_buffer_s *apb,
-              uint16_t status);
-#endif
 
 #ifndef CONFIG_AUDIO_EXCLUDE_FFORWARD
-static int  pcm_subsample_configure(FAR struct pcm_decode_s *priv,
+static void pcm_subsample_configure(FAR struct pcm_decode_s *priv,
               uint8_t subsample);
-#ifdef CONFIG_AUDIO_MULTI_SESSION
-static void pcm_subsample_callback(FAR struct pcm_decode_s *priv,
-              uint16_t reason, FAR struct ap_buffer_s *apb,
-              uint16_t status, FAR void *session);
-#else
-static void pcm_subsample_callback(FAR struct pcm_decode_s *priv,
-              uint16_t reason, FAR struct ap_buffer_s *apb,
-              uint16_t status);
-#endif
-static FAR struct ap_buffer_s *pcm_subsample(FAR struct pcm_decode_s *priv,
+static void pcm_subsample(FAR struct pcm_decode_s *priv,
               FAR struct ap_buffer_s *apb);
 #endif
 
@@ -446,39 +418,6 @@ static bool pcm_parsewav(FAR struct pcm_decode_s *priv, uint8_t *data)
 }
 
 /****************************************************************************
- * Name: pcm_upper_callback
- *
- * Description:
- *   The lower level driver has just returned a buffer that belongs to the
- *   uppder level.  We need to forward the buffer to the upper level for
- *   disposition.
- *
- ****************************************************************************/
-
-#ifdef CONFIG_AUDIO_MULTI_SESSION
-static void pcm_upper_callback(FAR struct pcm_decode_s *priv,
-              uint16_t reason, FAR struct ap_buffer_s *apb,
-              uint16_t status, FAR void *session)
-#else
-static void pcm_upper_callback(FAR struct pcm_decode_s *priv,
-              uint16_t reason, FAR struct ap_buffer_s *apb,
-              uint16_t status)
-#endif
-{
-  DEBUGASSERT(priv && apb && priv->export.upper);
-
-  /* The buffer belongs to to an upper level.  Just forward the event to
-   * the next level up.
-   */
-
-#ifdef CONFIG_AUDIO_MULTI_SESSION
-  priv->export.upper(priv->export.priv, reason, apb, status, session);
-#else
-  priv->export.upper(priv->export.priv, reason, apb, status);
-#endif
-}
-
-/****************************************************************************
  * Name: pcm_subsample_configure
  *
  * Description:
@@ -488,15 +427,9 @@ static void pcm_upper_callback(FAR struct pcm_decode_s *priv,
  ****************************************************************************/
 
 #ifndef CONFIG_AUDIO_EXCLUDE_FFORWARD
-static int pcm_subsample_configure(FAR struct pcm_decode_s *priv,
-                                   uint8_t subsample)
+static void pcm_subsample_configure(FAR struct pcm_decode_s *priv,
+                                    uint8_t subsample)
 {
-  FAR struct audio_lowerhalf_s *lower = priv->lower;
-#ifdef CONFIG_AUDIO_DRIVER_SPECIFIC_BUFFERS
-  struct ap_buffer_info_s bufinfo;
-#endif
-  int ret;
-
   audvdbg("subsample: %d\n", subsample);
 
   /* Three possibilities:
@@ -507,84 +440,18 @@ static int pcm_subsample_configure(FAR struct pcm_decode_s *priv,
 
   if (priv->subsample == AUDIO_SUBSAMPLE_NONE)
     {
-      /* There should be no audio buffer allocated in this case */
-
-      DEBUGASSERT(priv->ffwd == NULL);
-
       /* Ignore request to stop fast forwarding if we are already
        * fast forwarding.
        */
 
       if (subsample != AUDIO_SUBSAMPLE_NONE)
         {
-          /* Check if we already have an audio buffer.  This might happen in
-           * certain race conditions were we exit and return to fast forward
-           * mode while the audio buffer is in possession of the lower level
-           * driver.
-           */
-
-          audvdbg("Start subsampling: apb=%p\n", priv->apb);
-
-          /* REVISIT: I think we could get rid of this special buffer.  It
-           * seems like we should be able to do the sub-sampling in place
-           * without any additional buffers.
-           */
-
-          if (priv->apb == NULL)
-            {
-#ifdef CONFIG_AUDIO_DRIVER_SPECIFIC_BUFFERS
-              /* Get the lower level driver's preferred buffer properties */
-
-              DEBUGASSERT(lower->ioctl);
-              ret = lower->ioctl(lower, AUDIOIOC_GETBUFFERINFO,
-                                 (unsigned long)&bufinfo))
-              if (ret < 0)
-                {
-                  /* Driver doesn't report it's buffer size.  Use defaults. */
-
-                  bufinfo.buffer_size = CONFIG_AUDIO_BUFFER_NUMBYTES;
-                  bufinfo.nbuffers    = CONFIG_AUDIO_NUM_BUFFERS;
-                }
-#endif
-
-              /* Configure the buffer descriptor */
-
-#ifdef CONFIG_AUDIO_MULTI_SESSION
-              priv->bufdesc.session    = priv->session;
-#endif
-#ifdef CONFIG_AUDIO_DRIVER_SPECIFIC_BUFFERS
-              priv->bufdesc.numbytes   = bufinfo.buffer_size;
-#else
-              priv->bufdesc.numbytes   = CONFIG_AUDIO_BUFFER_NUMBYTES;
-#endif
-              priv->bufdesc.u.ppBuffer = &priv->apb;
-
-              /* Perform the allocation */
-
-              if (lower->ops->allocbuffer)
-                {
-                  ret = lower->ops->allocbuffer(lower, &priv->bufdesc);
-                }
-              else
-                {
-                  ret = apb_alloc(&priv->bufdesc);
-                }
-
-              /* Did we get an audio buffer? */
-
-              if (ret < 0 || priv->apb == NULL)
-                {
-                  auddbg("ERROR: Failed to allocate an audio buffer\n");
-                  return -ENOMEM;
-                }
-            }
+          audvdbg("Start sub-sampling\n");
 
           /* Save the current subsample setting. Subsampling will begin on
            * then next audio buffer that we receive.
            */
 
-          priv->ffwd      = priv->apb;
-          priv->next      = NULL;
           priv->npartial  = 0;
           priv->skip      = 0;
           priv->subsample = subsample;
@@ -592,15 +459,11 @@ static int pcm_subsample_configure(FAR struct pcm_decode_s *priv,
     }
 
   /* 2. Were already fast forwarding and we have been asked to change the
-   *    subsampling rate.
+   *    sub-sampling rate.
    */
 
   else if (subsample != AUDIO_SUBSAMPLE_NONE)
     {
-      /* We should already have an audio buffer allocated in this case */
-
-      DEBUGASSERT(priv->apb != NULL && priv->ffwd != NULL);
-
       /* Just save the current subsample setting.  It will take effect
        * on the next audio buffer that we receive.
        */
@@ -614,159 +477,16 @@ static int pcm_subsample_configure(FAR struct pcm_decode_s *priv,
 
   else if (subsample != AUDIO_SUBSAMPLE_NONE)
     {
-      DEBUGASSERT(priv->apb != NULL && priv->ffwd != NULL);
-
-      audvdbg("Stop subsampling\n");
-
-      /* Are still holding on to buffers that belong the upper level? */
-
-      if (priv->ffwd && priv->ffwd != priv->apb)
-        {
-#ifdef CONFIG_AUDIO_MULTI_SESSION
-          pcm_upper_callback(priv, AUDIO_CALLBACK_DEQUEUE, priv->ffwd, OK, priv->session);
-#else
-          pcm_upper_callback(priv, AUDIO_CALLBACK_DEQUEUE, priv->ffwd, OK);
-#endif
-          priv->ffwd = NULL;
-        }
-
-      /* We need to free the our working audio buffer.  But we also need
-       * to be careful:  The lower level audio driver may have it now.
-       *
-       * If the lower level driver has the audio buffer, then we will defer
-       * freeing it until it is returned to us.
-       */
-
-      if (priv->ffwd)
-        {
-          /* We have it.  We can free the audio buffer.  NOTE:  This audio
-           * buffer might not be empty, but we will discard it anyway.
-           * Playing will begin at normal speed at the next, full audio
-           * buffer.
-           */
+      audvdbg("Stop sub-sampling\n");
 
-          if (lower->ops->freebuffer)
-            {
-              (void)lower->ops->freebuffer(lower, &priv->bufdesc);
-            }
-          else
-            {
-              apb_free(priv->apb);
-            }
-
-          priv->apb   = NULL;
-          priv->ffwd  = NULL;
-        }
-
-      /* And indicate that we are in normal play mode.  This will take
-       * effect when the next audio buffer is received.
+      /* Indicate that we are in normal play mode.  This will take effect
+       * when the next audio buffer is received.
        */
 
-      priv->next      = NULL;
       priv->npartial  = 0;
       priv->skip      = 0;
       priv->subsample = AUDIO_SUBSAMPLE_NONE;
     }
-
-  return OK;
-}
-#endif
-
-/****************************************************************************
- * Name: pcm_subsample_callback
- *
- * Description:
- *   Our working audio buffer has been returned from the lower level driver.
- *
- ****************************************************************************/
-
-#ifndef CONFIG_AUDIO_EXCLUDE_FFORWARD
-#ifdef CONFIG_AUDIO_MULTI_SESSION
-static void pcm_subsample_callback(FAR struct pcm_decode_s *priv,
-                                   uint16_t reason,
-                                   FAR struct ap_buffer_s *apb,
-                                   uint16_t status, FAR void *session)
-#else
-static void pcm_subsample_callback(FAR struct pcm_decode_s *priv,
-                                   uint16_t reason,
-                                   FAR struct ap_buffer_s *apb,
-                                   uint16_t status)
-#endif
-{
-  FAR struct audio_lowerhalf_s *lower;
-
-  DEBUGASSERT(priv->apb);
-
-  audvdbg("apb=%p subsample=%d\n", apb, priv->subsample);
-
-  /* Mark the buffer as empty */
-
-  apb->nbytes  = 0;
-  apb->curbyte = 0;
-
-  /* Possibilities:
-   * 1. We are no longer streaming and we just need to free the buffer.
-   *    This case happens if we exited fast forward mode while the lower-
-   *    level driver had possession of or working audio buffer.
-   */
-
-  if (priv->subsample == AUDIO_SUBSAMPLE_NONE)
-    {
-      /* Free the working buffer */
-
-      lower = priv->lower;
-      if (lower->ops->freebuffer)
-        {
-          (void)lower->ops->freebuffer(lower, &priv->bufdesc);
-        }
-      else
-        {
-          apb_free(apb);
-        }
-
-      priv->apb = NULL;
-    }
-
-  /* We are still streaming.  At any given time, our working audio may be
-   * (a) the current working buffer, (a) the next working buffer or it, or
-   * (c) in possession of the lower level driver.  None of these are the
-   * case now since we just got our working audio buffer back from the
-   *
-   * 2. We have no fast forward working buffer.  Use it buffer as our
-   *    fast forward working buffer.  This should never happen.
-   */
-
-  else if (priv->ffwd == NULL)
-    {
-      /* Set the returned buffer as the current working buffer */
-
-      priv->ffwd = apb;
-    }
-
-  /* 2. We already have a fast word working buffer, but no next working
-   *    buffer.  Save out working audio buffer as the new next buffer.
-   */
-
-  else
-    {
-      /* Set the returned buffer as the next working buffer
-       *
-       * REVISIT:  This extra buffer is only used on the first buffer. There
-       * is something wrong:
-       *
-       * 1. First buffer: Our private buffer is the working buffer.  The
-       *    first audio buffer we receive is compressed into the working
-       *    buffer and the working buffer goes to the lower level.  The
-       *    first buffer becomes next working buffer.
-       * 2. Next buffers: Are compressed into the working buffer, sent
-       *    to the lower level, and become the next working buffer, etc.
-       * 3. The private buffer eventually comes back here and is saved
-       *    as the "next" buffer, but it is never used again.
-       */
-
-      DEBUGASSERT(priv->next == NULL);
-      priv->next = apb;
-    }
 }
 #endif
 
@@ -774,43 +494,42 @@ static void pcm_subsample_callback(FAR struct pcm_decode_s *priv,
  * Name: pcm_subsample
  *
  * Description:
- *   Given a newly received audio buffer, perform subsampling into our local
- *   working audio buffer.  Return the subsampled audio buffer to send to
- *   the lower level driver.
+ *   Given a newly received audio buffer, perform sub-sampling in-place in
+ *   the audio buffer.  Since the sub-sampled data will always be smaller
+ *   than the original buffer, no additional buffering should be necessary.
  *
  ****************************************************************************/
 
 #ifndef CONFIG_AUDIO_EXCLUDE_FFORWARD
-static FAR struct ap_buffer_s *pcm_subsample(FAR struct pcm_decode_s *priv,
-                                             FAR struct ap_buffer_s *apb)
+static void pcm_subsample(FAR struct pcm_decode_s *priv,
+                          FAR struct ap_buffer_s *apb)
 {
-  FAR struct ap_buffer_s *work;
   FAR const uint8_t *src;
   FAR uint8_t *dest;
   unsigned int destsize;
   unsigned int srcsize;
   unsigned int skipsize;
+  unsigned int copysize;
   unsigned int i;
 
-  /* Are we subsampling? */
+  /* Are we sub-sampling? */
 
   if (priv->subsample == AUDIO_SUBSAMPLE_NONE)
     {
       /* No.. do nothing to the buffer */
 
-      return apb;
+      return;
     }
 
-  /* Yes.. then make sure that we have the required buffers in place */
-
-  DEBUGASSERT(priv->ffwd && priv->apb);
-
-  /* Yes.. we will need to subsample the newly received buffer. */
+  /* Yes.. we will need to subsample the newly received buffer in-place by
+   * copying from the upper end of the buffer to the lower end.
+   */
 
-  work = priv->ffwd;
-  dest = &work->samp[work->nbytes];
+  src  = &apb->samp[apb->curbyte];
+  dest = apb->samp;
 
-  DEBUGASSERT(work->nmaxbytes >= priv->align);
+  srcsize  = apb->nbytes - apb->curbyte;
+  destsize = apb->nmaxbytes;
 
   /* This is the number of bytes that we need to skip between samples */
 
@@ -820,10 +539,6 @@ static FAR struct ap_buffer_s *pcm_subsample(FAR struct pcm_decode_s *priv,
 
   if (priv->npartial > 0)
     {
-      /* How much data is available in the new audio buffer */
-
-      srcsize = apb->nbytes - apb->curbyte;
-
       /* Let's get an impossible corner case out of the way.  What if we
        * received a tiny audio buffer.  So small, that it (plus any previous
        * sample) is smaller than one sample.
@@ -831,45 +546,46 @@ static FAR struct ap_buffer_s *pcm_subsample(FAR struct pcm_decode_s *priv,
 
       if (priv->npartial + srcsize < priv->align)
         {
-          /* Update the partial sample size */
+          /* Update the partial sample size and return the unmodified
+           * buffer.
+           */
 
           priv->npartial += srcsize;
-
-          /* And just return the buffer with no modification */
-
-          return apb;
+          return;
         }
 
-      /* No, we do at least have enough to complete the sample.  Copy copy data
-       * from the new audio buffer to complete the sample.
+      /* We do at least have enough to complete the sample.  If this data
+       * does not resides at the correct position at the from of the audio
+       * buffer, then we will need to copy it.
        */
 
-      src  = &apb->samp[apb->curbyte];
-      for (i = priv->npartial; i < priv->align; i++)
+      copysize = priv->align - priv->npartial;
+      if (apb->curbyte > 0)
         {
-          *dest++ = *src++;
-          apb->curbyte++;
-        }
+          /* We have to copy down */
 
-      priv->npartial = 0;
+          for (i = 0; i < copysize; i++)
+            {
+              *dest++ = *src++;
+            }
+        }
 
-      /* Update the number of bytes in the working buffer and reset the skip
-       * value
+      /* Update the number of bytes in the working buffer and reset the
+       * skip value
        */
 
-      work->nbytes += skipsize;
-      priv->skip    = skipsize;
+      priv->npartial = 0;
+      srcsize       -= copysize;
+      destsize      -= copysize;
+      priv->skip     = skipsize;
     }
 
-  /* Now loop until either (1) the working audio buffer is full, or (2)
-   * the newly received audio buffer is empty.
+  /* Now loop until either the entire audio buffer has been sub-sampling.
+   * This copy in place works because we know that the sub-sampled data
+   * will always be smaller than the original data.
    */
 
-  src      = &apb->samp[apb->curbyte];
-  srcsize  = apb->nbytes - apb->curbyte;
-  destsize = work->nmaxbytes - work->nbytes;
-
-  while (srcsize > 0 && destsize > 0)
+  while (srcsize > 0)
     {
       /* Do we need to skip ahead in the buffer? */
 
@@ -880,26 +596,17 @@ static FAR struct ap_buffer_s *pcm_subsample(FAR struct pcm_decode_s *priv,
            * number of bytes available in the newly received audio buffer.
            */
 
-          unsigned int discard = MIN(priv->skip, srcsize);
+          copysize    = MIN(priv->skip, srcsize);
 
-          priv->skip   -= discard;
-          apb->curbyte += discard;
-          srcsize      -= discard;
-
-          /* Did we skip to the end of the audio buffer? */
-
-          if (srcsize <= 0)
-            {
-              goto exit_apb_empty;
-            }
+          priv->skip -= copysize;
+          src        += copysize;
+          srcsize    -= copysize;
         }
 
       /* Copy the sample from the audio buffer into the working buffer. */
 
       else
         {
-          unsigned int copysize;
-
           /* Do we have space for the whole sample? */
 
           if (srcsize < priv->align)
@@ -911,149 +618,32 @@ static FAR struct ap_buffer_s *pcm_subsample(FAR struct pcm_decode_s *priv,
             }
           else
             {
+              /* Copy the whole sample and re-arm the skip size */
+
               copysize       = priv->align;
               priv->skip     = skipsize;
             }
 
-          /* Now copy the sample from new audio buffer to working buffer */
+          /* Now copy the sample from the end of audio buffer to the beginning. */
 
           for (i = 0; i < copysize; i++)
             {
               *dest++ = *src++;
             }
 
-          /* Update indices and sizes and reset the skip value */
-
-          apb->curbyte  += copysize;
-          srcsize       -= copysize;
-
-          work->nbytes  += copysize;
-          destsize      -= copysize;
-        }
-    }
-
-  /* We get here in one of two cases.  Either (1) the source audio buffer
-   * became empty, and/or (2) the working audio buffer became which.  Which
-   * is the case?
-   *
-   * REVISIT:  Should there be a threshold here so that we do not send
-   * really tiny buffers to the lower-level driver.
-   */
-
-  if (srcsize > 0)
-    {
-      /* How could the working buffer be empty in this case? */
-
-      DEBUGASSERT(work->nbytes > 0);
-
-      /* This seems overly complex.  We either need another buffer or else
-       * we have to do this:  Sub-ample in place.
-       */
-
-      dest     = apb->samp;
-      destsize = apb->nmaxbytes;
-
-      while (srcsize > 0)
-        {
-          /* Do we need to skip ahead in the buffer? */
-
-          if (priv->skip > 0)
-            {
-              /* How much can we skip in this buffer?  Depends on the
-               * smaller of (1) the number of bytes that we need to skip
-               * and (2) the number of bytes available in the audio buffer.
-               */
-
-              unsigned int discard = MIN(priv->skip, srcsize);
-
-              priv->skip   -= discard;
-              srcsize      -= discard;
-
-              /* Did we skip to the end of the audio buffer? */
-
-              if (srcsize <= 0)
-                {
-                  break;
-                }
-            }
-
-          /* Copy the sample from the end of the audio buffer to the beginning. */
-
-          else
-            {
-              unsigned int copysize;
-
-              /* Do we have space for the whole sample? */
-
-              if (srcsize < priv->align)
-                {
-                  /* No.. this is a partial copy */
-
-                  copysize       = srcsize;
-                  priv->npartial = srcsize;
-                }
-              else
-                {
-                  /* Copy the whole sample and re-arm the skip size */
-
-                  copysize       = priv->align;
-                  priv->skip     = skipsize;
-                }
-
-              /* Now copy the sample from new audio buffer to working buffer */
-
-              for (i = 0; i < copysize; i++)
-                {
-                  *dest++ = *src++;
-                }
-
-              /* Updates bytes available in the source buffer and bytes
-               * remaining in the dest buffer.
-               */
+          /* Updates bytes available in the source buffer and bytes
+           * remaining in the destination buffer.
+           */
 
-              srcsize  -= copysize;
-              destsize -= copysize;
-            }
+          srcsize  -= copysize;
+          destsize -= copysize;
         }
-
-      /* Set the buffer that we just emptied as the new working buffer */
-
-      apb->curbyte = 0;
-      apb->nbytes  = apb->nmaxbytes - destsize;
-      priv->ffwd   = apb;
-
-      /* Return the working buffer */
-
-      return work;
     }
 
-exit_apb_empty:
-  /* We get here in the case that the source audio buffer is empty.  The
-   * working buffer may be empty or non-empty.
-   */
-
-  /* Is there anything in the working buffer?
-   *
-   * REVISIT:  Should there be a threshold here so that we do not send
-   * really tiny buffers to the lower-level driver.
-   */
-
-  if (work->nbytes > 0)
-    {
-      /* Set the buffer that we just emptied as the new working buffer */
-
-      apb->curbyte = 0;
-      apb->nbytes  = 0;
-      priv->ffwd   = apb;
+  /* Update the size and offset data in the audio buffer */
 
-      /* Return the working buffer */
-
-      return work;
-    }
-
-  /* We don't have any data to forward to the lower level driver */
-
-  return NULL;
+  apb->curbyte = 0;
+  apb->nbytes  = apb->nmaxbytes - destsize;
 }
 #endif
 
@@ -1129,9 +719,6 @@ static int pcm_configure(FAR struct audio_lowerhalf_s *dev,
 {
   FAR struct pcm_decode_s *priv = (FAR struct pcm_decode_s *)dev;
   FAR struct audio_lowerhalf_s *lower;
-#ifndef CONFIG_AUDIO_EXCLUDE_FFORWARD
-  int ret;
-#endif
 
   DEBUGASSERT(priv);
 
@@ -1144,19 +731,13 @@ static int pcm_configure(FAR struct audio_lowerhalf_s *dev,
   if (caps->ac_type == AUDIO_TYPE_PROCESSING &&
       caps->ac_format.hw == AUDIO_PU_SUBSAMPLE_FORWARD)
     {
-      /* Configure subsampling */
-
-      ret = pcm_subsample_configure(priv, caps->ac_controls.b[0]);
-      if (ret < 0)
-        {
-          auddbg("ERROR: pcm_subsample_configure failed: %d\n", ret);
-        }
-
-      /* Return to avoid forwarding the configuration to the lower level
+      /* Configure sub-sampling and return to avoid forwarding the
+       * configuration to the lower level
        * driver.
        */
 
-      return ret;
+      pcm_subsample_configure(priv, caps->ac_controls.b[0]);
+      return OK;
     }
 #endif
 
@@ -1440,21 +1021,17 @@ static int pcm_enqueuebuffer(FAR struct audio_lowerhalf_s *dev,
       audvdbg("Received: apb=%p curbyte=%d nbytes=%d\n",
               apb, apb->curbyte, apb->nbytes);
 
-      /* Perform any necessary subsampling operations */
+      /* Perform any necessary sub-sampling operations */
 
-      apb = pcm_subsample(priv, apb);
-      if (apb)
+      pcm_subsample(priv, apb);
 #endif
-        {
-          /* Then give the audio buffer to the lower driver */
 
-          audvdbg("Pass to lower enqueuebuffer: apb=%p curbyte=%d nbytes=%d\n",
-                  apb, apb->curbyte, apb->nbytes);
+      /* Then give the audio buffer to the lower driver */
 
-          return lower->ops->enqueuebuffer(lower, apb);
-        }
+      audvdbg("Pass to lower enqueuebuffer: apb=%p curbyte=%d nbytes=%d\n",
+              apb, apb->curbyte, apb->nbytes);
 
-      return OK;
+      return lower->ops->enqueuebuffer(lower, apb);
     }
 
   /* No.. then this must be the first buffer that we have seen (since we
@@ -1511,21 +1088,17 @@ static int pcm_enqueuebuffer(FAR struct audio_lowerhalf_s *dev,
           audvdbg("Begin streaming: apb=%p curbyte=%d nbytes=%d\n",
                   apb, apb->curbyte, apb->nbytes);
 
-          /* Perform any necessary subsampling operations */
+          /* Perform any necessary sub-sampling operations */
 
-          apb = pcm_subsample(priv, apb);
-          if (apb)
+          pcm_subsample(priv, apb);
 #endif
-            {
-              /* Then give the audio buffer to the lower driver */
 
-              audvdbg("Pass to lower enqueuebuffer: apb=%p curbyte=%d nbytes=%d\n",
-                      apb, apb->curbyte, apb->nbytes);
+          /* Then give the audio buffer to the lower driver */
 
-              return lower->ops->enqueuebuffer(lower, apb);
-            }
+          audvdbg("Pass to lower enqueuebuffer: apb=%p curbyte=%d nbytes=%d\n",
+                  apb, apb->curbyte, apb->nbytes);
 
-          return OK;
+          return lower->ops->enqueuebuffer(lower, apb);
         }
     }
 
@@ -1690,63 +1263,31 @@ static int pcm_release(FAR struct audio_lowerhalf_s *dev)
  *
  ****************************************************************************/
 
-/* Audio callback */
-
 #ifdef CONFIG_AUDIO_MULTI_SESSION
-
 static void pcm_callback(FAR void *arg, uint16_t reason,
                          FAR struct ap_buffer_s *apb, uint16_t status,
                          FAR void *session)
-{
-  FAR struct pcm_decode_s *priv = (FAR struct pcm_decode_s *)arg;
-
-#ifndef CONFIG_AUDIO_EXCLUDE_FFORWARD
-  /* If this is our internal working audio buffer that we use for subsampling,
-   * then we are the owner of the buffer and we don't want to return it to
-   * the upper level.
-   */
-
-  if (priv->apb == apb)
-    {
-      pcm_subsample_callback(priv, reason, apb, status, session);
-    }
-  else
-#endif
-    {
-      /* Return the buffer to the upper level */
-
-      pcm_upper_callback(priv, reason, apb, status, session);
-    }
-}
-
-#else /* CONFIG_AUDIO_MULTI_SESSION */
-
+#else
 static void pcm_callback(FAR void *arg, uint16_t reason,
                          FAR struct ap_buffer_s *apb, uint16_t status)
+#endif
 {
   FAR struct pcm_decode_s *priv = (FAR struct pcm_decode_s *)arg;
 
-#ifndef CONFIG_AUDIO_EXCLUDE_FFORWARD
-  /* If this is our internal working audio buffer that we use for sub-sampling,
-   * then we are the owner of the buffer and we don't want to return it to
-   * the upper level.
+
+  DEBUGASSERT(priv && apb && priv->export.upper);
+
+  /* The buffer belongs to to an upper level.  Just forward the event to
+   * the next level up.
    */
 
-  if (priv->apb == apb)
-    {
-      pcm_subsample_callback(priv, reason, apb, status);
-    }
-  else
+#ifdef CONFIG_AUDIO_MULTI_SESSION
+  priv->export.upper(priv->export.priv, reason, apb, status, session);
+#else
+  priv->export.upper(priv->export.priv, reason, apb, status);
 #endif
-    {
-      /* Return the buffer to the upper level */
-
-      pcm_upper_callback(priv, reason, apb, status);
-    }
 }
 
-#endif /* CONFIG_AUDIO_MULTI_SESSION */
-
 /****************************************************************************
  * Public Functions
  ****************************************************************************/