Audio: Add a NULL audio device that can be used to simply unit-level testing of audio decoders

4 files changed, 824 insertions, 9 deletions

diff --git a/nuttx/drivers/audio/Kconfig b/nuttx/drivers/audio/Kconfig
index c6649750f..039b8a0dd 100644
--- a/nuttx/drivers/audio/Kconfig
+++ b/nuttx/drivers/audio/Kconfig
@@ -106,5 +106,57 @@ config AUDIO_WM8904
 		that dependency is not explicit here.
 
 if AUDIO_WM8904
+
+config WM8904_INITVOLUME
+	int "WM8904 initial volume setting"
+	default 250
+
+config WM8904_INFLIGHT
+	int "WM8904 maximum in-flight audio buffers"
+	default 2
+
+config WM8904_MSG_PRIO
+	int "WM8904 message priority"
+	default 1
+
+config WM8904_BUFFER_SIZE
+	int "WM8904 preferred buffer size"
+	default 8192
+
+config WM8904_NUM_BUFFERS
+	int "WM8904 preferred number of buffers"
+	default 4
+
+config WM8904_WORKER_STACKSIZE
+	int "WM8904 worker thread stack size"
+	default 768
+
 endif # AUDIO_WM8904
 
+config AUDIO_NULL
+	bool "NULL audio device"
+	default n
+	depends on AUDIO
+	---help---
+		A do-nothinig audio device driver to simplify testing of audio
+		decoders.
+
+if AUDIO_NULL
+
+config AUDIO_NULL_MSG_PRIO
+	int "Null audio device message priority"
+	default 1
+
+config UDIO_NULL_BUFFER_SIZE
+	int "Null audio device preferred buffer size"
+	default 8192
+
+config AUDIO_NULL_NUM_BUFFERS
+	int "Null audio device preferred number of buffers"
+	default 4
+
+config AUDIO_NULL_WORKER_STACKSIZE
+	int "Null audio device worker thread stack size"
+	default 768
+
+endif # AUDIO_NULL
diff --git a/nuttx/drivers/audio/Make.defs b/nuttx/drivers/audio/Make.defs
index 72bb16b1a..2b8e97818 100644
--- a/nuttx/drivers/audio/Make.defs
+++ b/nuttx/drivers/audio/Make.defs
@@ -47,6 +47,10 @@ ifeq ($(CONFIG_AUDIO_WM8904),y)
 CSRCS += wm8904.c
 endif
 
+ifeq ($(CONFIG_AUDIO_NULL),y)
+CSRCS += audio_null.c
+endif
+
 ifeq ($(CONFIG_AUDIO_I2SCHAR),y)
 CSRCS += i2schar.c
 endif
diff --git a/nuttx/drivers/audio/audio_null.c b/nuttx/drivers/audio/audio_null.c
new file mode 100644
index 000000000..ea59921de
--- /dev/null
+++ b/nuttx/drivers/audio/audio_null.c
@@ -0,0 +1,764 @@
+/****************************************************************************
+ * drivers/audio/audio_null.c
+ *
+ * A do-nothinig audio device driver to simplify testing of audio decoders.
+ *
+ *   Copyright (C) 2014 Gregory Nutt. All rights reserved.
+ *   Author:  Gregory Nutt <gnutt@nuttx.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name NuttX nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <sys/types.h>
+#include <sys/ioctl.h>
+
+#include <stdint.h>
+#include <stdio.h>
+#include <fcntl.h>
+#include <string.h>
+#include <errno.h>
+#include <queue.h>
+#include <debug.h>
+
+#include <nuttx/kmalloc.h>
+#include <nuttx/fs/fs.h>
+#include <nuttx/fs/ioctl.h>
+#include <nuttx/audio/audio.h>
+#include <nuttx/audio/audio_null.h>
+
+/****************************************************************************
+ * Private Definitions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Types
+ ****************************************************************************/
+
+struct null_dev_s
+{
+  struct audio_lowerhalf_s dev; /* Audio lower half (this device) */
+  mqd_t         mq;             /* Message queue for receiving messages */
+  char          mqname[16];     /* Our message queue name */
+  pthread_t     threadid;       /* ID of our thread */
+#ifndef CONFIG_AUDIO_EXCLUDE_STOP
+  volatile bool terminate;      /* True: request to terminate */
+#endif
+};
+
+/****************************************************************************
+ * Private Function Prototypes
+ ****************************************************************************/
+
+static int      null_getcaps(FAR struct audio_lowerhalf_s *dev, int type,
+                  FAR struct audio_caps_s *caps);
+#ifdef CONFIG_AUDIO_MULTI_SESSION
+static int      null_configure(FAR struct audio_lowerhalf_s *dev,
+                  FAR void *session, FAR const struct audio_caps_s *caps);
+#else
+static int      null_configure(FAR struct audio_lowerhalf_s *dev,
+                  FAR const struct audio_caps_s *caps);
+#endif
+static int      null_shutdown(FAR struct audio_lowerhalf_s *dev);
+static void    *null_workerthread(pthread_addr_t pvarg);
+#ifdef CONFIG_AUDIO_MULTI_SESSION
+static int      null_start(FAR struct audio_lowerhalf_s *dev,
+                  FAR void *session);
+#else
+static int      null_start(FAR struct audio_lowerhalf_s *dev);
+#endif
+#ifndef CONFIG_AUDIO_EXCLUDE_STOP
+#ifdef CONFIG_AUDIO_MULTI_SESSION
+static int      null_stop(FAR struct audio_lowerhalf_s *dev,
+                  FAR void* session);
+#else
+static int      null_stop(FAR struct audio_lowerhalf_s *dev);
+#endif
+#endif
+#ifndef CONFIG_AUDIO_EXCLUDE_PAUSE_RESUME
+#ifdef CONFIG_AUDIO_MULTI_SESSION
+static int      null_pause(FAR struct audio_lowerhalf_s *dev,
+                  FAR void* session);
+static int      null_resume(FAR struct audio_lowerhalf_s *dev,
+                  FAR void* session);
+#else
+static int      null_pause(FAR struct audio_lowerhalf_s *dev);
+static int      null_resume(FAR struct audio_lowerhalf_s *dev);
+#endif
+#endif
+static int      null_enqueuebuffer(FAR struct audio_lowerhalf_s *dev,
+                  FAR struct ap_buffer_s *apb);
+static int      null_cancelbuffer(FAR struct audio_lowerhalf_s *dev,
+                  FAR struct ap_buffer_s *apb);
+static int      null_ioctl(FAR struct audio_lowerhalf_s *dev, int cmd,
+                  unsigned long arg);
+#ifdef CONFIG_AUDIO_MULTI_SESSION
+static int      null_reserve(FAR struct audio_lowerhalf_s *dev,
+                  FAR void **session);
+#else
+static int      null_reserve(FAR struct audio_lowerhalf_s *dev);
+#endif
+#ifdef CONFIG_AUDIO_MULTI_SESSION
+static int      null_release(FAR struct audio_lowerhalf_s *dev,
+                  FAR void *session);
+#else
+static int      null_release(FAR struct audio_lowerhalf_s *dev);
+#endif
+
+/****************************************************************************
+ * Private Data
+ ****************************************************************************/
+
+static const struct audio_ops_s g_audioops =
+{
+  null_getcaps,       /* getcaps        */
+  null_configure,     /* configure      */
+  null_shutdown,      /* shutdown       */
+  null_start,         /* start          */
+#ifndef CONFIG_AUDIO_EXCLUDE_STOP
+  null_stop,          /* stop           */
+#endif
+#ifndef CONFIG_AUDIO_EXCLUDE_PAUSE_RESUME
+  null_pause,         /* pause          */
+  null_resume,        /* resume         */
+#endif
+  NULL,               /* allocbuffer    */
+  NULL,               /* freebuffer     */
+  null_enqueuebuffer, /* enqueue_buffer */
+  null_cancelbuffer,  /* cancel_buffer  */
+  null_ioctl,         /* ioctl          */
+  NULL,               /* read           */
+  NULL,               /* write          */
+  null_reserve,       /* reserve        */
+  null_release        /* release        */
+};
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: null_getcaps
+ *
+ * Description: Get the audio device capabilities
+ *
+ ****************************************************************************/
+
+static int null_getcaps(FAR struct audio_lowerhalf_s *dev, int type,
+                          FAR struct audio_caps_s *caps)
+{
+  audvdbg("Entry\n");
+
+  /* Validate the structure */
+
+  DEBUGASSERT(caps->ac_len >= sizeof(struct audio_caps_s));
+
+  /* Fill in the caller's structure based on requested info */
+
+  caps->ac_format[0]   = 0;
+  caps->ac_format[1]   = 0;
+  caps->ac_controls[0] = 0;
+  caps->ac_controls[1] = 0;
+  caps->ac_controls[2] = 0;
+  caps->ac_controls[3] = 0;
+
+  switch (caps->ac_type)
+    {
+      /* Caller is querying for the types of units we support */
+
+      case AUDIO_TYPE_QUERY:
+
+        /* Provide our overall capabilities.  The interfacing software
+         * must then call us back for specific info for each capability.
+         */
+
+        caps->ac_channels = 2;       /* Stereo output */
+
+        switch (caps->ac_subtype)
+          {
+            case AUDIO_TYPE_QUERY:
+              /* We don't decode any formats!  Only something above us in
+               * the audio stream can perform decoding on our behalf.
+               */
+
+              /* The types of audio units we implement */
+
+              caps->ac_controls[0] = AUDIO_TYPE_OUTPUT | AUDIO_TYPE_FEATURE |
+                                     AUDIO_TYPE_PROCESSING;
+
+              break;
+
+            case AUDIO_FMT_MIDI:
+              /* We only support Format 0 */
+
+              caps->ac_controls[0] = AUDIO_SUBFMT_END;
+              break;
+
+            default:
+              caps->ac_controls[0] = AUDIO_SUBFMT_END;
+              break;
+          }
+
+        break;
+
+      /* Provide capabilities of our OUTPUT unit */
+
+      case AUDIO_TYPE_OUTPUT:
+
+        caps->ac_channels = 2;
+
+        switch (caps->ac_subtype)
+          {
+            case AUDIO_TYPE_QUERY:
+
+              /* Report the Sample rates we support */
+
+              caps->ac_controls[0] = AUDIO_SAMP_RATE_8K | AUDIO_SAMP_RATE_11K |
+                                     AUDIO_SAMP_RATE_16K | AUDIO_SAMP_RATE_22K |
+                                     AUDIO_SAMP_RATE_32K | AUDIO_SAMP_RATE_44K |
+                                     AUDIO_SAMP_RATE_48K;
+              break;
+
+            case AUDIO_FMT_MP3:
+            case AUDIO_FMT_WMA:
+            case AUDIO_FMT_PCM:
+              break;
+
+            default:
+              break;
+          }
+
+        break;
+
+      /* Provide capabilities of our FEATURE units */
+
+      case AUDIO_TYPE_FEATURE:
+
+        /* If the sub-type is UNDEF, then report the Feature Units we support */
+
+        if (caps->ac_subtype == AUDIO_FU_UNDEF)
+          {
+            /* Fill in the ac_controls section with the Feature Units we have */
+
+            caps->ac_controls[0] = AUDIO_FU_VOLUME | AUDIO_FU_BASS | AUDIO_FU_TREBLE;
+            caps->ac_controls[1] = AUDIO_FU_BALANCE >> 8;
+          }
+        else
+          {
+            /* TODO:  Do we need to provide specific info for the Feature Units,
+             * such as volume setting ranges, etc.?
+             */
+          }
+
+        break;
+
+      /* Provide capabilities of our PROCESSING unit */
+
+      case AUDIO_TYPE_PROCESSING:
+
+        switch (caps->ac_subtype)
+          {
+            case AUDIO_PU_UNDEF:
+
+              /* Provide the type of Processing Units we support */
+
+              caps->ac_controls[0] = AUDIO_PU_STEREO_EXTENDER;
+              break;
+
+            case AUDIO_PU_STEREO_EXTENDER:
+
+              /* Provide capabilities of our Stereo Extender */
+
+              caps->ac_controls[0] = AUDIO_STEXT_ENABLE | AUDIO_STEXT_WIDTH;
+              break;
+
+            default:
+
+              /* Other types of processing uint we don't support */
+
+              break;
+          }
+
+        break;
+
+      /* All others we don't support */
+
+      default:
+
+        /* Zero out the fields to indicate no support */
+
+        caps->ac_subtype = 0;
+        caps->ac_channels = 0;
+
+        break;
+    }
+
+  /* Return the length of the audio_caps_s struct for validation of
+   * proper Audio device type.
+   */
+
+  audvdbg("Return %d\n", caps->ac_len);
+  return caps->ac_len;
+}
+
+/****************************************************************************
+ * Name: null_configure
+ *
+ * Description:
+ *   Configure the audio device for the specified  mode of operation.
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_AUDIO_MULTI_SESSION
+static int null_configure(FAR struct audio_lowerhalf_s *dev,
+                            FAR void *session,
+                            FAR const struct audio_caps_s *caps)
+#else
+static int null_configure(FAR struct audio_lowerhalf_s *dev,
+                            FAR const struct audio_caps_s *caps)
+#endif
+{
+  audvdbg("Return OK\n");
+  return OK;
+}
+
+/****************************************************************************
+ * Name: null_shutdown
+ *
+ * Description:
+ *   Shutdown the driver and put it in the lowest power state possible.
+ *
+ ****************************************************************************/
+
+static int null_shutdown(FAR struct audio_lowerhalf_s *dev)
+{
+  audvdbg("Return OK\n");
+  return OK;
+}
+
+/****************************************************************************
+ * Name: null_workerthread
+ *
+ *  This is the thread that feeds data to the chip and keeps the audio
+ *  stream going.
+ *
+ ****************************************************************************/
+
+static void *null_workerthread(pthread_addr_t pvarg)
+{
+  FAR struct null_dev_s *priv = (struct null_dev_s *) pvarg;
+  struct audio_msg_s msg;
+  int msglen;
+  int prio;
+
+  audvdbg("Entry\n");
+
+  /* Loop as long as we are supposed to be running */
+
+#ifndef CONFIG_AUDIO_EXCLUDE_STOP
+  while (!priv->terminate)
+#else
+  for (;;)
+#endif
+    {
+      /* Wait for messages from our message queue */
+
+      msglen = mq_receive(priv->mq, &msg, sizeof(msg), &prio);
+
+      /* Handle the case when we return with no message */
+
+      if (msglen < sizeof(struct audio_msg_s))
+        {
+          auddbg("ERROR: Message too small: %d\n", msglen);
+          continue;
+        }
+
+      /* Process the message */
+
+      switch (msg.msgId)
+        {
+          case AUDIO_MSG_DATA_REQUEST:
+            break;
+
+#ifndef CONFIG_AUDIO_EXCLUDE_STOP
+          case AUDIO_MSG_STOP:
+            priv->terminate = true;
+            break;
+#endif
+
+          case AUDIO_MSG_ENQUEUE:
+            break;
+
+          case AUDIO_MSG_COMPLETE:
+            break;
+
+          default:
+            auddbg("ERROR: Ignoring message ID %d\n", msg.msgId);
+            break;
+        }
+    }
+
+  /* Close the message queue */
+
+  mq_close(priv->mq);
+  mq_unlink(priv->mqname);
+  priv->mq = NULL;
+
+  /* Send an AUDIO_MSG_COMPLETE message to the client */
+
+#ifdef CONFIG_AUDIO_MULTI_SESSION
+  priv->dev.upper(priv->dev.priv, AUDIO_CALLBACK_COMPLETE, NULL, OK, NULL);
+#else
+  priv->dev.upper(priv->dev.priv, AUDIO_CALLBACK_COMPLETE, NULL, OK);
+#endif
+
+  audvdbg("Exit\n");
+  return NULL;
+}
+
+/****************************************************************************
+ * Name: null_start
+ *
+ * Description:
+ *   Start the configured operation (audio streaming, volume enabled, etc.).
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_AUDIO_MULTI_SESSION
+static int null_start(FAR struct audio_lowerhalf_s *dev, FAR void *session)
+#else
+static int null_start(FAR struct audio_lowerhalf_s *dev)
+#endif
+{
+  FAR struct null_dev_s *priv = (FAR struct null_dev_s *)dev;
+  struct sched_param sparam;
+  struct mq_attr attr;
+  pthread_attr_t tattr;
+  FAR void *value;
+  int ret;
+
+  audvdbg("Entry\n");
+
+  /* Create a message queue for the worker thread */
+
+  snprintf(priv->mqname, sizeof(priv->mqname), "/tmp/%X", priv);
+
+  attr.mq_maxmsg  = 16;
+  attr.mq_msgsize = sizeof(struct audio_msg_s);
+  attr.mq_curmsgs = 0;
+  attr.mq_flags   = 0;
+
+  priv->mq = mq_open(priv->mqname, O_RDWR | O_CREAT, 0644, &attr);
+  if (priv->mq == NULL)
+    {
+      /* Error creating message queue! */
+
+      auddbg("ERROR: Couldn't allocate message queue\n");
+      return -ENOMEM;
+    }
+
+  /* Join any old worker thread we had created to prevent a memory leak */
+
+  if (priv->threadid != 0)
+    {
+      audvdbg("Joining old thread\n");
+      pthread_join(priv->threadid, &value);
+    }
+
+  /* Start our thread for sending data to the device */
+
+  pthread_attr_init(&tattr);
+  sparam.sched_priority = sched_get_priority_max(SCHED_FIFO) - 3;
+  (void)pthread_attr_setschedparam(&tattr, &sparam);
+  (void)pthread_attr_setstacksize(&tattr, CONFIG_AUDIO_NULL_WORKER_STACKSIZE);
+
+  audvdbg("Starting worker thread\n");
+  ret = pthread_create(&priv->threadid, &tattr, null_workerthread,
+                       (pthread_addr_t)priv);
+  if (ret != OK)
+    {
+      auddbg("ERROR: pthread_create failed: %d\n", ret);
+    }
+  else
+    {
+      pthread_setname_np(priv->threadid, "null audio");
+      audvdbg("Created worker thread\n");
+    }
+
+  audvdbg("Return %d\n", ret);
+  return ret;
+}
+
+/****************************************************************************
+ * Name: null_stop
+ *
+ * Description: Stop the configured operation (audio streaming, volume
+ *              disabled, etc.).
+ *
+ ****************************************************************************/
+
+#ifndef CONFIG_AUDIO_EXCLUDE_STOP
+#ifdef CONFIG_AUDIO_MULTI_SESSION
+static int null_stop(FAR struct audio_lowerhalf_s *dev, FAR void* session)
+#else
+static int null_stop(FAR struct audio_lowerhalf_s *dev)
+#endif
+{
+  FAR struct null_dev_s *priv = (FAR struct null_dev_s *)dev;
+  struct audio_msg_s term_msg;
+  FAR void *value;
+
+  /* Send a message to stop all audio streaming */
+
+  term_msg.msgId = AUDIO_MSG_STOP;
+  term_msg.u.data = 0;
+  mq_send(priv->mq, &term_msg, sizeof(term_msg), CONFIG_AUDIO_NULL_MSG_PRIO);
+
+  /* Join the worker thread */
+
+  pthread_join(priv->threadid, &value);
+  priv->threadid = 0;
+
+  audvdbg("Return OK\n");
+  return OK;
+}
+#endif
+
+/****************************************************************************
+ * Name: null_pause
+ *
+ * Description: Pauses the playback.
+ *
+ ****************************************************************************/
+
+#ifndef CONFIG_AUDIO_EXCLUDE_PAUSE_RESUME
+#ifdef CONFIG_AUDIO_MULTI_SESSION
+static int null_pause(FAR struct audio_lowerhalf_s *dev, FAR void* session)
+#else
+static int null_pause(FAR struct audio_lowerhalf_s *dev)
+#endif
+{
+  audvdbg("Return OK\n");
+  return OK;
+}
+#endif /* CONFIG_AUDIO_EXCLUDE_PAUSE_RESUME */
+
+/****************************************************************************
+ * Name: null_resume
+ *
+ * Description: Resumes the playback.
+ *
+ ****************************************************************************/
+
+#ifndef CONFIG_AUDIO_EXCLUDE_PAUSE_RESUME
+#ifdef CONFIG_AUDIO_MULTI_SESSION
+static int null_resume(FAR struct audio_lowerhalf_s *dev, FAR void* session)
+#else
+static int null_resume(FAR struct audio_lowerhalf_s *dev)
+#endif
+{
+  audvdbg("Return OK\n");
+  return OK;
+}
+#endif /* CONFIG_AUDIO_EXCLUDE_PAUSE_RESUME */
+
+/****************************************************************************
+ * Name: null_enqueuebuffer
+ *
+ * Description: Enqueue an Audio Pipeline Buffer for playback/ processing.
+ *
+ ****************************************************************************/
+
+static int null_enqueuebuffer(FAR struct audio_lowerhalf_s *dev,
+                                FAR struct ap_buffer_s *apb)
+{
+  /* Take a reference */
+
+  apb_reference(apb);
+
+  /* say that we consumed all of the data */
+
+  apb->curbyte = apb->nbytes;
+
+  /* Release the reference and return success */
+
+  apb_free(apb);
+
+  audvdbg("Return OK\n");
+  return OK;
+}
+
+/****************************************************************************
+ * Name: null_cancelbuffer
+ *
+ * Description: Called when an enqueued buffer is being cancelled.
+ *
+ ****************************************************************************/
+
+static int null_cancelbuffer(FAR struct audio_lowerhalf_s *dev,
+                               FAR struct ap_buffer_s *apb)
+{
+  audvdbg("Return OK\n");
+  return OK;
+}
+
+/****************************************************************************
+ * Name: null_ioctl
+ *
+ * Description: Perform a device ioctl
+ *
+ ****************************************************************************/
+
+static int null_ioctl(FAR struct audio_lowerhalf_s *dev, int cmd,
+                        unsigned long arg)
+{
+#ifdef CONFIG_AUDIO_DRIVER_SPECIFIC_BUFFERS
+  FAR struct ap_buffer_info_s *bufinfo;
+#endif
+
+  /* Deal with ioctls passed from the upper-half driver */
+
+  switch (cmd)
+    {
+      /* Check for AUDIOIOC_HWRESET ioctl.  This ioctl is passed straight
+       * through from the upper-half audio driver.
+       */
+
+      case AUDIOIOC_HWRESET:
+        break;
+
+       /* Report our preferred buffer size and quantity */
+
+#ifdef CONFIG_AUDIO_DRIVER_SPECIFIC_BUFFERS
+      case AUDIOIOC_GETBUFFERINFO:
+        bufinfo              = (FAR struct ap_buffer_info_s *) arg;
+        bufinfo->buffer_size = CONFIG_AUDIO_NULL_BUFFER_SIZE;
+        bufinfo->nbuffers    = CONFIG_AUDIO_NULL_NUM_BUFFERS;
+        break;
+#endif
+
+      default:
+        break;
+    }
+
+  audvdbg("Return OK\n");
+  return OK;
+}
+
+/****************************************************************************
+ * Name: null_reserve
+ *
+ * Description: Reserves a session (the only one we have).
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_AUDIO_MULTI_SESSION
+static int null_reserve(FAR struct audio_lowerhalf_s *dev,
+                          FAR void **session)
+#else
+static int null_reserve(FAR struct audio_lowerhalf_s *dev)
+#endif
+{
+  audvdbg("Return OK\n");
+  return OK;
+}
+
+/****************************************************************************
+ * Name: null_release
+ *
+ * Description: Releases the session (the only one we have).
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_AUDIO_MULTI_SESSION
+static int null_release(FAR struct audio_lowerhalf_s *dev,
+                          FAR void *session)
+#else
+static int null_release(FAR struct audio_lowerhalf_s *dev)
+#endif
+{
+  FAR struct null_dev_s *priv = (FAR struct null_dev_s *)dev;
+  void  *value;
+
+  /* Join any old worker thread we had created to prevent a memory leak */
+
+  if (priv->threadid != 0)
+    {
+      pthread_join(priv->threadid, &value);
+      priv->threadid = 0;
+    }
+
+  return OK;
+}
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: audio_null_initialize
+ *
+ * Description:
+ *   Initialize the null audio device.
+ *
+ * Input Parameters:
+ *   i2c     - An I2C driver instance
+ *   i2s     - An I2S driver instance
+ *   lower   - Persistent board configuration data
+ *
+ * Returned Value:
+ *   A new lower half audio interface for the NULL audio device is returned
+ *   on success; NULL is returned on failure.
+ *
+ ****************************************************************************/
+
+FAR struct audio_lowerhalf_s *audio_null_initialize(void)
+{
+  FAR struct null_dev_s *priv;
+
+  /* Allocate the null audio device structure */
+
+  priv = (FAR struct null_dev_s *)kzalloc(sizeof(struct null_dev_s));
+  if (priv)
+    {
+      /* Initialize the null audio device structure.  Since we used kzalloc,
+       * only the non-zero elements of the structure need to be initialized.
+       */
+
+      priv->dev.ops = &g_audioops;
+      return &priv->dev;
+    }
+
+  return NULL;
+}
diff --git a/nuttx/drivers/audio/wm8904.c b/nuttx/drivers/audio/wm8904.c
index d37ef116c..2a85505d8 100644
--- a/nuttx/drivers/audio/wm8904.c
+++ b/nuttx/drivers/audio/wm8904.c
@@ -95,7 +95,7 @@ struct wm8904_dev_s
    * "half" that is referred to as "lower".
    */
 
-  struct audio_lowerhalf_s dev;             /* WM8904 audio lower half (this drive) */
+  struct audio_lowerhalf_s dev;             /* WM8904 audio lower half (this device) */
 
   /* Our specific driver data goes here */
 
@@ -181,15 +181,10 @@ static int      wm8904_stop(FAR struct audio_lowerhalf_s *dev);
 #ifdef CONFIG_AUDIO_MULTI_SESSION
 static int      wm8904_pause(FAR struct audio_lowerhalf_s *dev,
                   FAR void* session);
-#else
-static int      wm8904_pause(FAR struct audio_lowerhalf_s *dev);
-#endif
-#endif
-#ifndef CONFIG_AUDIO_EXCLUDE_PAUSE_RESUME
-#ifdef CONFIG_AUDIO_MULTI_SESSION
 static int      wm8904_resume(FAR struct audio_lowerhalf_s *dev,
                   FAR void* session);
 #else
+static int      wm8904_pause(FAR struct audio_lowerhalf_s *dev);
 static int      wm8904_resume(FAR struct audio_lowerhalf_s *dev);
 #endif
 #endif
@@ -1755,8 +1750,8 @@ static void wm8904_audio_input(FAR struct wm8904_dev_s *priv)
  *   lower   - Persistent board configuration data
  *
  * Returned Value:
- *   A new lower half audio interface is returned for the WM8904 device is
- *   returned on success; NULL is returned on failure.
+ *   A new lower half audio interface for the WM8904 device is returned on
+ *   success; NULL is returned on failure.
  *
  ****************************************************************************/