Add audio/ sub-syste, include/nuttx/audio.h interface, and drivers/audio/vs1053.c driver to NuttX. From Ken Pettit

5 files changed, 983 insertions, 0 deletions

diff --git a/nuttx/audio/Kconfig b/nuttx/audio/Kconfig
new file mode 100644
index 000000000..a666c775f
--- /dev/null
+++ b/nuttx/audio/Kconfig
@@ -0,0 +1,89 @@
+#
+# For a description of the syntax of this configuration file,
+# see misc/tools/kconfig-language.txt.
+#
+
+config AUDIO
+	bool "Audio Support"
+	default n
+	---help---
+		Enables overall support for Audio library.
+
+if AUDIO
+
+config AUDIO_NCHANNELS
+	int "Number of Audio Channels"
+	default 2
+	---help---
+		Stereo channel support is standard, but some systems may support 5 or 7
+		channel capability.
+
+config AUDIO_LARGE_BUFFERS
+	bool "Support Audio Buffers with greater than 65K samples"
+	default n
+	---help---
+		By default, the Audio Pipeline Buffer uses a 16-bit max sample count, limiting
+		the number of samples per buffer to 65K.  Enable this option to specify a
+		32-bit max sample count for increased samples / buffer capability.
+		channel capability.
+
+menu "Supported Audio Formats"
+
+config AUDIO_FORMAT_PCM
+	bool "PCM Audio"
+	default y
+	---help---
+		Build in support for PCM Audio format.
+
+config AUDIO_FORMAT_MP3
+	bool "MPEG 3 Layer 1"
+	default n
+	---help---
+		Build in support for MP3 Audio format.
+
+config AUDIO_FORMAT_WMA
+	bool "WMA Format (see copyright notice)"
+	default n
+	---help---
+		Add in support for Microsoft Windows Media format.
+
+config AUDIO_FORMAT_OGG_VORBIS
+	bool "Ogg Vorbis format"
+	default n
+	---help---
+		Build in support for the Open Source Ogg Vorbis format.
+
+endmenu
+
+# These are here as placeholders of what could be added 
+
+if CONFIG_AUDIO_PLANNED
+
+config AUDIO_MIXER
+	bool "Planned - Enable support for the software based Audio Mixer"
+	default n
+	---help---
+		The Audio mixer is a software-only based component that can be used
+		to perform audio channel or device mixing.
+
+config AUDIO_MIDI_SYNTH
+	bool "Planned - Enable support for the software-based MIDI synthisizer"
+	default n
+	---help---
+		Builds a simple MIDI synthisizer.
+
+config AUDIO_OUTPUT_JACK_CONTROL
+	bool "Planned - Enable support for output jack control"
+	default n
+	---help---
+		Builds a simple MIDI synthisizer.
+
+config AUDIO_FONT
+	bool "Planned - Enable support for the Audio Font"
+	default n
+	---help---
+		The Audio font provides common audio symbols.
+
+endif
+
+endif
diff --git a/nuttx/audio/Makefile b/nuttx/audio/Makefile
new file mode 100644
index 000000000..b6c111621
--- /dev/null
+++ b/nuttx/audio/Makefile
@@ -0,0 +1,101 @@
+############################################################################
+# audio/Makefile
+#
+#   Copyright (C) 2013 Ken Pettit. All rights reserved.
+#   Author: Ken Pettit <pettitkd@gmail.com>
+#
+# 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.
+#
+############################################################################
+
+-include $(TOPDIR)/Make.defs
+DELIM ?= $(strip /)
+
+ifeq ($(WINTOOL),y)
+INCDIROPT = -w
+endif
+
+DEPPATH = --dep-path .
+ASRCS =
+CSRCS = audio.c buffer.c
+VPATH = .
+
+# Include support for various drivers.  Each Make.defs file will add its
+# files to the source file list, add its DEPPATH info, and will add
+# the appropriate paths to the VPATH variable
+
+ifeq ($(CONFIG_AUDIO_FORMAT_PCM),y)
+  CSRCS += pcm.c
+endif
+
+ifeq ($(CONFIG_AUDIO_MIXER),y)
+  CSRCS += mixer.c
+endif
+
+ifeq ($(CONFIG_AUDIO_MIDI_SYNTH),y)
+  CSRCS += midisynth.c
+endif
+
+ifeq ($(CONFIG_AUDIO_FONT),y)
+  CSRCS += audio_font.c
+endif
+
+AOBJS = $(ASRCS:.S=$(OBJEXT))
+COBJS = $(CSRCS:.c=$(OBJEXT))
+
+SRCS = $(ASRCS) $(CSRCS)
+OBJS = $(AOBJS) $(COBJS)
+
+BIN = libaudio$(LIBEXT)
+
+all: $(BIN)
+
+$(AOBJS): %$(OBJEXT): %.S
+	$(call ASSEMBLE, $<, $@)
+
+$(COBJS): %$(OBJEXT): %.c
+	$(call COMPILE, $<, $@)
+
+$(BIN): $(OBJS)
+	$(call ARCHIVE, $@, $(OBJS))
+
+.depend: Makefile $(SRCS)
+	$(Q) $(MKDEP) $(DEPPATH) "$(CC)" -- $(CFLAGS) -- $(SRCS) >Make.dep
+	$(Q) touch $@
+
+depend: .depend
+
+clean:
+	$(call DELFILE, $(BIN))
+	$(call CLEAN)
+
+distclean: clean
+	$(call DELFILE, Make.dep)
+	$(call DELFILE, .depend)
+
+-include Make.dep
diff --git a/nuttx/audio/audio.c b/nuttx/audio/audio.c
new file mode 100644
index 000000000..4457294f9
--- /dev/null
+++ b/nuttx/audio/audio.c
@@ -0,0 +1,534 @@
+/****************************************************************************
+ * audio/audio.c
+ *
+ *   Copyright (C) 2013 Ken Pettit. All rights reserved.
+ *   Author: Ken Pettit <pettitkd@gmail.com>
+ *
+ * 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.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Compilation Switches
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <semaphore.h>
+#include <fcntl.h>
+#include <assert.h>
+#include <errno.h>
+#include <debug.h>
+
+#include <nuttx/kmalloc.h>
+#include <nuttx/fs/fs.h>
+#include <nuttx/arch.h>
+#include <nuttx/audio.h>
+
+#include <arch/irq.h>
+
+#ifdef CONFIG_AUDIO
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+/* Debug ********************************************************************/
+/* Non-standard debug that may be enabled just for testing Audio */
+
+#ifndef AUDIO_MAX_DEVICE_PATH
+#  define AUDIO_MAX_DEVICE_PATH 32
+#endif
+
+/****************************************************************************
+ * Private Type Definitions
+ ****************************************************************************/
+
+/* This structure describes the state of the upper half driver */
+
+struct audio_upperhalf_s
+{
+  uint8_t           crefs;    /* The number of times the device has been opened */
+  volatile bool     started;  /* True: pulsed output is being generated */
+  sem_t             exclsem;  /* Supports mutual exclusion */
+  struct audio_info_s info;     /* Pulsed output characteristics */
+  FAR struct audio_lowerhalf_s *dev;  /* lower-half state */
+};
+
+/****************************************************************************
+ * Private Function Prototypes
+ ****************************************************************************/
+
+static int     audio_open(FAR struct file *filep);
+static int     audio_close(FAR struct file *filep);
+static ssize_t audio_read(FAR struct file *filep, FAR char *buffer, size_t buflen);
+static ssize_t audio_write(FAR struct file *filep, FAR const char *buffer, size_t buflen);
+static int     audio_start(FAR struct audio_upperhalf_s *upper, unsigned int oflags);
+static int     audio_ioctl(FAR struct file *filep, int cmd, unsigned long arg);
+
+/****************************************************************************
+ * Private Data
+ ****************************************************************************/
+
+static const struct file_operations g_audioops =
+{
+  audio_open,  /* open */
+  audio_close, /* close */
+  audio_read,  /* read */
+  audio_write, /* write */
+  0,         /* seek */
+  audio_ioctl  /* ioctl */
+#ifndef CONFIG_DISABLE_POLL
+  , 0        /* poll */
+#endif
+};
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/************************************************************************************
+ * Name: audio_open
+ *
+ * Description:
+ *   This function is called whenever the Audio device is opened.
+ *
+ ************************************************************************************/
+
+static int audio_open(FAR struct file *filep)
+{
+  FAR struct inode           *inode = filep->f_inode;
+  FAR struct audio_upperhalf_s *upper = inode->i_private;
+  uint8_t                     tmp;
+  int                         ret;
+
+  audvdbg("crefs: %d\n", upper->crefs);
+
+  /* Get exclusive access to the device structures */
+
+  ret = sem_wait(&upper->exclsem);
+  if (ret < 0)
+    {
+      ret = -errno;
+      goto errout;
+    }
+
+  /* Increment the count of references to the device.  If this the first
+   * time that the driver has been opened for this device, then initialize
+   * the device.
+   */
+
+  tmp = upper->crefs + 1;
+  if (tmp == 0)
+    {
+      /* More than 255 opens; uint8_t overflows to zero */
+
+      ret = -EMFILE;
+      goto errout_with_sem;
+    }
+
+  /* Save the new open count on success */
+
+  upper->crefs = tmp;
+  ret = OK;
+
+errout_with_sem:
+  sem_post(&upper->exclsem);
+  
+errout:
+  return ret;
+}
+
+/************************************************************************************
+ * Name: audio_close
+ *
+ * Description:
+ *   This function is called when the Audio device is closed.
+ *
+ ************************************************************************************/
+
+static int audio_close(FAR struct file *filep)
+{
+  FAR struct inode           *inode = filep->f_inode;
+  FAR struct audio_upperhalf_s *upper = inode->i_private;
+  int                         ret;
+
+  audvdbg("crefs: %d\n", upper->crefs);
+
+  /* Get exclusive access to the device structures */
+
+  ret = sem_wait(&upper->exclsem);
+  if (ret < 0)
+    {
+      ret = -errno;
+      goto errout;
+    }
+
+  /* Decrement the references to the driver.  If the reference count will
+   * decrement to 0, then uninitialize the driver.
+   */
+
+  if (upper->crefs > 1)
+    {
+      upper->crefs--;
+    }
+  else
+    {
+      FAR struct audio_lowerhalf_s *lower = upper->dev;
+
+      /* There are no more references to the port */
+
+      upper->crefs = 0;
+
+      /* Disable the Audio device */
+
+      DEBUGASSERT(lower->ops->shutdown != NULL);
+      audvdbg("calling shutdown: %d\n");
+
+      lower->ops->shutdown(lower);
+    }
+  ret = OK;
+
+//errout_with_sem:
+  sem_post(&upper->exclsem);
+  
+errout:
+  return ret;
+}
+
+/************************************************************************************
+ * Name: audio_read
+ *
+ * Description:
+ *   A dummy read method.  This is provided only to satsify the VFS layer.
+ *
+ ************************************************************************************/
+
+static ssize_t audio_read(FAR struct file *filep, FAR char *buffer, size_t buflen)
+{
+  /* Return zero -- usually meaning end-of-file */
+
+  return 0;
+}
+
+/************************************************************************************
+ * Name: audio_write
+ *
+ * Description:
+ *   A dummy write method.  This is provided only to satsify the VFS layer.
+ *
+ ************************************************************************************/
+
+static ssize_t audio_write(FAR struct file *filep, FAR const char *buffer, size_t buflen)
+{
+  return 0;
+}
+
+/************************************************************************************
+ * Name: audio_start
+ *
+ * Description:
+ *   Handle the AUDIOIOC_START ioctl command
+ *   
+ ************************************************************************************/
+
+static int audio_start(FAR struct audio_upperhalf_s *upper, unsigned int oflags)
+{
+  FAR struct audio_lowerhalf_s *lower = upper->dev;
+  int ret = OK;
+
+  DEBUGASSERT(upper != NULL && lower->ops->start != NULL);
+
+  /* Verify that the Audio is not already running */
+
+  if (!upper->started)
+    {
+      /* Invoke the bottom half method to start the pulse train */
+
+      ret = lower->ops->start(lower);
+
+      /* A return value of zero means that the pulse train was started
+       * successfully.
+       */
+
+      if (ret == OK)
+        {
+          /* Indicate that the pulse train has started */
+
+          upper->started = true;
+        }
+    }
+
+  return ret;
+}
+
+/************************************************************************************
+ * Name: audio_ioctl
+ *
+ * Description:
+ *   The standard ioctl method.  This is where ALL of the Audio work is done.
+ *   
+ ************************************************************************************/
+
+static int audio_ioctl(FAR struct file *filep, int cmd, unsigned long arg)
+{
+  FAR struct inode           *inode = filep->f_inode;
+  FAR struct audio_upperhalf_s *upper = inode->i_private;
+  FAR struct audio_lowerhalf_s *lower = upper->dev;
+  int                         ret;
+
+  audvdbg("cmd: %d arg: %ld\n", cmd, arg);
+
+  /* Get exclusive access to the device structures */
+
+  ret = sem_wait(&upper->exclsem);
+  if (ret < 0)
+    {
+      return ret;
+    }
+
+  /* Handle built-in ioctl commands */
+
+  switch (cmd)
+    {
+      /* AUDIOIOC_GETCAPS - Get the audio device capabilities.
+       *
+       *   ioctl argument:  A pointer to the audio_caps_s structure.
+       */
+
+      case AUDIOIOC_GETCAPS:
+        {
+          FAR struct audio_caps_s *caps = (FAR struct audio_caps_s*)((uintptr_t)arg);
+          DEBUGASSERT(lower->ops->getcaps != NULL);
+
+          audvdbg("AUDIOIOC_GETCAPS: Device=%d", caps->ac_type);
+
+          /* Call the lower-half driver capabilities handler */
+          ret = lower->ops->getcaps(lower, caps->ac_type, caps);
+        }
+        break;
+
+      case AUDIOIOC_CONFIGURE:
+        {
+          FAR const struct audio_caps_s *caps = (FAR const struct audio_caps_s*)((uintptr_t)arg);
+          DEBUGASSERT(lower->ops->configure != NULL);
+
+          audvdbg("AUDIOIOC_INITIALIZE: Device=%d", caps->ac_type);
+
+          /* Call the lower-half driver configure handler */
+          ret = lower->ops->configure(lower, caps);
+        }
+        break;
+
+      case AUDIOIOC_SHUTDOWN:
+        {
+          DEBUGASSERT(lower->ops->shutdown != NULL);
+
+          audvdbg("AUDIOIOC_SHUTDOWN\n");
+
+          /* Call the lower-half driver initialize handler */
+          ret = lower->ops->shutdown(lower);
+        }
+        break;
+
+      /* AUDIOIOC_START - Start the pulsed output.  The AUDIOIOC_SETCHARACTERISTICS
+       *   command must have previously been sent.
+       *
+       *   ioctl argument:  None
+       */
+
+      case AUDIOIOC_START:
+        {
+          audvdbg("AUDIOIOC_START\n"); 
+          DEBUGASSERT(lower->ops->start != NULL);
+
+          /* Start the pulse train */
+
+          ret = audio_start(upper, filep->f_oflags);
+        }
+        break;
+
+      /* AUDIOIOC_STOP - Stop the pulsed output.
+       *
+       *   ioctl argument:  None
+       */
+
+      case AUDIOIOC_STOP:
+        {
+          audvdbg("AUDIOIOC_STOP\n");
+          DEBUGASSERT(lower->ops->stop != NULL);
+
+          if (upper->started)
+            {
+              ret = lower->ops->stop(lower);
+              upper->started = false;
+            }
+        }
+        break;
+
+      /* Any unrecognized IOCTL commands might be platform-specific ioctl commands */
+
+      default:
+        {
+          audvdbg("Forwarding unrecognized cmd: %d arg: %ld\n", cmd, arg);
+          DEBUGASSERT(lower->ops->ioctl != NULL);
+          ret = lower->ops->ioctl(lower, cmd, arg);
+        }
+        break;
+    }
+
+  sem_post(&upper->exclsem);
+  return ret;
+}
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: audio_register
+ *
+ * Description:
+ *   This function binds an instance of a "lower half" audio driver with the
+ *   "upper half" Audio device and registers that device so that can be used
+ *   by application code.
+ *
+ *   When this function is called, the "lower half" driver should be in the
+ *   reset state (as if the shutdown() method had already been called).
+ *
+ * Input parameters:
+ *   path - The full path to the driver to be registers in the NuttX pseudo-
+ *     filesystem.  The recommended convention is to name Audio drivers
+ *     based on the function they provide, such as "/dev/pcm0", "/dev/mp31", 
+ *     etc. 
+ *   dev - A pointer to an instance of lower half audio driver.  This instance
+ *     is bound to the Audio driver and must persists as long as the driver
+ *     persists.
+ *
+ * Returned Value:
+ *   Zero on success; a negated errno value on failure.
+ *
+ ****************************************************************************/
+
+int audio_register(FAR const char *name, FAR struct audio_lowerhalf_s *dev)
+{
+  FAR struct audio_upperhalf_s *upper;
+  char  path[AUDIO_MAX_DEVICE_PATH];
+  static bool dev_audio_created = false;
+  const char* devname = "/dev/audio";
+
+  /* Allocate the upper-half data structure */
+
+  upper = (FAR struct audio_upperhalf_s *)kzalloc(sizeof(struct audio_upperhalf_s));
+  if (!upper)
+    {
+      auddbg("Allocation failed\n");
+      return -ENOMEM;
+    }
+
+  /* Initialize the Audio device structure (it was already zeroed by kzalloc()) */
+
+  sem_init(&upper->exclsem, 0, 1);
+  upper->dev = dev;
+
+  /* Create a /dev/audio directory. */
+
+  if (!dev_audio_created)
+    {
+      /* We don't check for error here because even if it fails, then
+       * the register_driver call below will return an error condition
+       * for us.
+       */
+
+      mkdir(devname, 0644);
+      dev_audio_created = true;
+    }
+
+  /* Register the Audio device */
+
+  memset(path, 0, AUDIO_MAX_DEVICE_PATH);
+  strcpy(path, devname);
+  strcat(path, "/");
+  strncat(path, name, AUDIO_MAX_DEVICE_PATH - 11);
+
+  audvdbg("Registering %s\n", path);
+  return register_driver(path, &g_audioops, 0666, upper);
+}
+
+/****************************************************************************
+ * Name: audio_dequeuebuffer
+ *
+ * Description:
+ *   Dequeues a previously enqueued Audio Pipeline Buffer.
+ *
+ *   1. The upper half driver calls the enqueuebuffer method, providing the 
+ *      lower half driver with the ab_buffer to process.
+ *   2. The lower half driver's enqueuebuffer will either processes the
+ *      buffer directly, or more likely add it to a queue for processing
+ *      by a background thread or worker task.
+ *   3. When the lower half driver has completed processing of the enqueued
+ *      ab_buffer, it will call this routine to indicated processing of the
+ *      buffer is complete.
+ *   4. When this routine is called, it will check if any threads are waiting
+ *      to enqueue additional buffers and "wake them up" for further 
+ *      processing.
+ *
+ * Input parameters:
+ *   handle - This is the handle that was provided to the lower-half
+ *     start() method.
+ *   apb - A pointer to the previsously enqueued ap_buffer_s
+ *
+ * Returned Value:
+ *   None
+ *
+ * Assumptions:
+ *   This function may be called from an interrupt handler.
+ *
+ ****************************************************************************/
+
+void audio_dequeuebuffer(FAR void *handle, FAR struct ap_buffer_s *apb)
+{
+  //FAR struct audio_upperhalf_s *upper = (FAR struct audio_upperhalf_s *)handle;
+
+  audllvdbg("Entry\n");
+
+  /* TODO:  Implement the logic */
+
+}
+
+#endif /* CONFIG_AUDIO */
diff --git a/nuttx/audio/buffer.c b/nuttx/audio/buffer.c
new file mode 100644
index 000000000..d6c6ac930
--- /dev/null
+++ b/nuttx/audio/buffer.c
@@ -0,0 +1,165 @@
+/****************************************************************************
+ * audio/buffer.c
+ *
+ *   Copyright (C) 2013 Ken Pettit. All rights reserved.
+ *   Author: Ken Pettit <pettitkd@gmail.com>
+ *
+ * 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 <stdint.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+#include <semaphore.h>
+#include <errno.h>
+#include <debug.h>
+
+#include <nuttx/kmalloc.h>
+#include <nuttx/audio.h>
+#include <nuttx/usb/audio.h>
+
+#if defined(CONFIG_AUDIO)
+
+/****************************************************************************
+ * Preprocessor Definitions
+ ****************************************************************************/
+
+/* Configuration ************************************************************/
+
+/****************************************************************************
+ * Private Types
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Variables
+ ****************************************************************************/
+
+/****************************************************************************
+ * Public Variables
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: apb_semtake
+ *
+ *       Take an Audio Pipeline Buffer.
+ *
+ ****************************************************************************/
+
+static void apb_semtake(sem_t *sem)
+{
+  /* Take the semaphore (perhaps waiting) */
+
+  while (sem_wait(sem) != 0)
+    {
+      /* The only case that an error should occr here is if
+       * the wait was awakened by a signal.
+       */
+
+      ASSERT(errno == EINTR);
+    }
+}
+
+/****************************************************************************
+ * Name: apb_semgive
+ ****************************************************************************/
+
+#define apb_semgive(s) sem_post(s)
+
+/****************************************************************************
+ * Name: apb_alloc
+ *
+ * Allocate an Audio Pipeline Buffer for use in the Audio sub-system.  This
+ * will perform the actual allocate based on buffer data format, number of
+ * channels, etc. and prepare the buffer for consumption.
+ *
+ ****************************************************************************/
+
+FAR struct ap_buffer_s *apb_alloc(int type, int sampleCount)
+{
+  /* TODO:  Implement the alloc logic */
+
+  return NULL;
+}
+
+/****************************************************************************
+ * Name: apb_prepare
+ *
+ * Prepare an AP Buffer for use in the Audio Pipeline.
+ *
+ ****************************************************************************/
+
+void apb_prepare(FAR struct ap_buffer_s *apb, int8_t allocmode, uint8_t format,
+    uint8_t subformat, apb_samp_t maxsamples)
+{
+  /* Perform a reference count decrement and possibly release the memory */
+
+}
+
+/****************************************************************************
+ * Name: apb_free
+ *
+ * Free's a previously allocated or referenced Audio Pipeline Buffer
+ *
+ ****************************************************************************/
+
+void apb_free(FAR struct ap_buffer_s *apb)
+{
+  /* Perform a reference count decrement and possibly release the memory */
+
+}
+
+/****************************************************************************
+ * Name: apb_reference
+ *
+ * Claim a reference to an Audio Pipeline Buffer.  Each call to apb_reference
+ * will increment the reference count and must have a matching apb_free
+ * call.  When the refcount decrements to zero, the buffer will be freed.
+ *
+ ****************************************************************************/
+
+void apb_reference(FAR struct ap_buffer_s *apb)
+{
+  /* TODO:  Implement the reference logic */
+}
+
+#endif /* CONFIG_AUDIO */
+
diff --git a/nuttx/audio/pcm.c b/nuttx/audio/pcm.c
new file mode 100644
index 000000000..4f77c67c5
--- /dev/null
+++ b/nuttx/audio/pcm.c
@@ -0,0 +1,94 @@
+/****************************************************************************
+ * audio/pcm.c
+ *
+ *   Copyright (C) 2013 Ken Pettit. All rights reserved.
+ *   Author: Ken Pettit <pettitkd@gmail.com>
+ *
+ * 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 <stdint.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+#include <semaphore.h>
+#include <errno.h>
+#include <debug.h>
+
+#include <nuttx/kmalloc.h>
+#include <nuttx/audio.h>
+
+#if defined(CONFIG_AUDIO) && defined(CONFIG_AUDIO_FORMAT_PCM)
+
+/****************************************************************************
+ * Preprocessor Definitions
+ ****************************************************************************/
+
+/* Configuration ************************************************************/
+
+/****************************************************************************
+ * Private Types
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Variables
+ ****************************************************************************/
+
+/****************************************************************************
+ * Public Variables
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: audio_pcm_init
+ *
+ * Initialized the Audio PCM library.
+ *
+ ****************************************************************************/
+
+int audio_pcm_initialize(void)
+{
+  /* Initialze the Audio PCM routines */
+
+  return OK;
+}
+
+#endif /* CONFIG_AUDIO && CONFIG_AUDIO_FORMAT_PCM */
+