From ddd6b7d383b9d1ad02e69ae09e7a38ea45a608d5 Mon Sep 17 00:00:00 2001
From: patacongo <patacongo@7fd9a85b-ad96-42d3-883c-3090e2eb8679>
Date: Sat, 11 Feb 2012 00:32:53 +0000
Subject: [PATCH] Add a RAM-based logging device

git-svn-id: https://nuttx.svn.sourceforge.net/svnroot/nuttx/trunk@4379 7fd9a85b-ad96-42d3-883c-3090e2eb8679
---
 nuttx/ChangeLog                          |   3 +
 nuttx/Documentation/NuttX.html           | 127 ++++-
 nuttx/configs/stm3210e-eval/src/up_adc.c |   3 +-
 nuttx/drivers/Makefile                   |   4 +
 nuttx/drivers/README.txt                 |  13 +
 nuttx/drivers/ramlog.c                   | 590 +++++++++++++++++++++++
 6 files changed, 734 insertions(+), 6 deletions(-)
 create mode 100644 nuttx/drivers/ramlog.c

diff --git a/nuttx/ChangeLog b/nuttx/ChangeLog
index a5856e50f9..1de3de5f0f 100644
--- a/nuttx/ChangeLog
+++ b/nuttx/ChangeLog
@@ -2450,4 +2450,7 @@
 	* fs/fat/fs_fatfs.c:  Fix and error in the FAT statfs() implementation that
 	  was causing some block counts to be reported incorrectly (reported by
 	  David Sidrane).
+	* drivers/ramlog.c:  Add a character driver that can substitute
+	  for /dev/console and or be used for logging debug output when there
+	  is no serial port available (such as when a telnet console is used).
 
diff --git a/nuttx/Documentation/NuttX.html b/nuttx/Documentation/NuttX.html
index 51ac872aa2..c604b9dad4 100644
--- a/nuttx/Documentation/NuttX.html
+++ b/nuttx/Documentation/NuttX.html
@@ -8,7 +8,7 @@
   <tr align="center" bgcolor="#e4e4e4">
     <td>
       <h1><big><font color="#3c34ec"><i>NuttX RTOS</i></font></big></h1>
-      <p>Last Updated: February 4, 2012</p>
+      <p>Last Updated: February 9, 2012</p>
     </td>
   </tr>
 </table>
@@ -707,7 +707,6 @@
       <li>Touchscreen, USB keyboard, GPIO-based buttons and keypads. </li>
     </p>
 </tr>
-</table></center>
 
 <tr>
   <td valign="top" width="22"><img height="20" width="20" src="favicon.ico"></td>
@@ -719,7 +718,21 @@
   <td><br></td>
   <td>
     <p>
-      <li>Support for Analog-to-Digital converters.</li>
+      <li>Support for Analog-to-Digital conversion (ADC) and Digital-to-Analog conversion (DAC).</li>
+    </p>
+</tr>
+
+<tr>
+  <td valign="top" width="22"><img height="20" width="20" src="favicon.ico"></td>
+  <td bgcolor="#5eaee1">
+    <b>Motor Control</b>
+  </td>
+</tr>
+<tr>
+  <td><br></td>
+  <td>
+    <p>
+      <li>Pulse width modulation (PWM) / Pulse count modulation.</li>
     </p>
 </tr>
 </table></center>
@@ -2838,9 +2851,115 @@ buildroot-1.10 2011-05-06 &lt;gnutt@nuttx.org&gt;
 <ul><pre>
 nuttx-6.15 2012-xx-xx Gregory Nutt &lt;gnutt@nuttx.org&gt;
 
+    * arch/arm/src/stm32/stm32_pwm.c:  Pulse count was limited to 128; now is
+      (essentially) unlimited.
+    * configs/stm3240g-eval/include/board.h:  Input frequences wrong for all but
+      one APB2 timer.
+    * arch/mips/src/pic32mx/pic32mx-ethernet.c:  The PIC32 Ethernet driver is
+      code complete, but still untested.
+    * confgs/sim/*/Make.defs and arch/sim/src/Makefile:  Add support for building
+      a 32-bit executable on a 64-bit Linux target.
+    * configs/sure-pic32mx/src/up_leds.c:  Correct GPIOs used for LEDs. The wrong
+      pins were being used.
+    * arch/arm/src/stm32/chip/stm32f10xxx_gpio.h: Correct offset to one AFIO EXICR
+      register.
+    * arch/arm/src/lpc17xx/lpc17_can.c:  Added &quot;advanced&quot; configuration options
+      to specify the CAN TSEG1 and TSEG2 clock counts specifically.
+    * include/nuttx/can.h and drivers/can.c:  Add support for extended (29-bit)
+      CAN IDs.
+    * arch/arm/src/lpc17xx/lpc17_can.c:  Add support for extended (29-bit) CAN IDs.
+    * arch/arm/src/stm32/stm32_can.c:  Add support for extended (29-bit) CAN IDs.
+    * include/nuttx/power/pm.h:  Move include/nuttx/pm.h into a sub-directory named
+      power.
+    * drivers/power:  Rename the drivers/pm directory to power
+    * include/power/battery.h and drivers/battery.c:  Add the interface definitions
+      for an upper and lower half battery driver.  Add the implementation of the
+      common upper half battery driver.
+    * drivers/power/max1704x.c:  Add a driver for MAX17040x battery &quot;fuel guage&quot;
+    * arch/arm/src/stm32/stm32_i2c.c: Add support for I2C3
+    * drivers/usbdev/: Lots of name changes: cdc_serial->cdcacm, usbstrg->usbmsc, 
+      usbser->pl2303
+    * drivers/usbdev/composite: Fleshed out support for a composite USB device.
+    * drivers/stm3210e-eval/composite and drivers/stm3210e-eval/src/up_composite.c:
+      Add a configuration test the USB composite device.
+    * include/nuttx/usb/usb.h, drivers/usbdev/composite_descriptors.c, and
+      drivers/usbdev/cdcacm_descriptors.c:  Add support for the USB Interface
+      Association Descriptor (IAD)
+    * arch/arm/src/stm32/stm32_i2c.c: Correct a typo in STM32 I2C3 support
+      (submitted by Mike Smith)
+    * arch/*/src/Makefile:  Candidate solution for dependency issue in the board
+      sub-directory:  By making libboard.a a &quot;phony&quot; target, libboard.a should
+      always rebuilt (the end result is worth the small increase in build time)
+      (submitted by Mike Smith).
+    * include/net/psock.h:  Added a new low level socket interface that allows the
+      OS to use the socket interface without having a socket descriptor.
+    * include/net/psock.h: Removed psock.h.  The new interfaces are moved into
+      nuttx/net.h which already has similar logic.
+    * include/nuttx/usb/usb.h: Can't use 'class' as a field name in USB structures.
+      This upsets C++ if usb.h is included. 'class' -> 'classid' in this header
+      file and all places that referenced 'class'
+    * drivers/usbdev/usbmsc.c: Fixed some backward conditional compilation.
+    * sched/on_exit.c:  Add support for the on_exit() function.,
+    * sched/exit.c, task_exithook.c, task_delete.c, sched_releasetcb.c:  Move
+      the logic that closes file descriptors sooner in the task shutdown sequence.
+      When drivers are closed, they may need to do things that require a fully
+      up-and-running task.  Some things cannot be done later when the task is
+      crippled.
+    * lib/dirent: Moved readdir_r() and telldir() from lib/misc to this new
+      directory where they belong.
+    * lib/termios.  Implemented tcsetattr() and tcgetattr().
+    * lib/stdio/lib_fgets.c:  The old fgets includes some terminal related
+      functionality:  It handles VT-100 commands, includes a command line editor
+      and echo characters back to the terminal.  This old, overloaded fgets()
+      was renamed readline() and moved to apps/system/readline.  The version
+      of fgets() in lib/stdio was them simplified and stripped down so that it
+      *only* gets a string -- as its description implies.
+    * arch/arm/src/lpc214x/lpc214x_usbdev.c:  Add corrections suggested by
+      David Hewson many, many months ago.
+    * configs/mcu123-lpc214x/composite and configs/mcu123-lpc214x/src/up_composite.c:
+      Add a configuration to test the USB composite device.
+    * configs/stm3240g-eval/telnetd:  Add a configuration for testing the
+      Telnet daemon.
+    * configs/stm3240g-eval/nsh2:  This is another NSH configuration.  It differs
+      from the original nsh configuration because it does not have an RS-232
+      console (only a Telnet console) and SDIO is enabled.  This configuration is
+      required because the STM3240G-EVAL board cannot simultaneously support
+      RS-232 and SDIO due to pin conflicts.
+    * lib/string/lib_strcasestr.c:  Add strcasestr().
+    * lib/stdio/lib_avsprintf.c:  Add avsprintf().
+    * lib/net/lib_inetntop.c:  Add inet_ntop().
+    * lib/net/lib_inetpton.c:  Add inet_pton().
+    * include/pthread.h:  Correct PTHREAD_MUTEX_INITIALIZER.
+    * fs/fat/fs_fatfs.c:  Fix and error in the FAT statfs() implementation that
+      was causing some block counts to be reported incorrectly (reported by
+      David Sidrane).
+
 apps-6.15 2012-xx-xx Gregory Nutt &lt;gnutt@nuttx.org&gt;
 
-pascal-3.1 2012-xx-xx Gregory Nutt &lt;gnutt@nuttx.org&gt;
+    * apps/nshlib/nsh_serial.c and nsh_usbdev.c:  If NuttX is configured to use
+      a USB serial console, then NSH needs to wait until the USB console is
+      connected and available.
+    * apps/examples/composite:  Add a test of the USB composite device.
+    * apps/examples/telnetd:  Move the tiny uIP shell example from
+      netutils/telnetd to examples/telnetd.  Enhanced the telnetd daemon so that
+      it supports telnetd via a TTY device driver: A new TTY device driver is
+      created when each new telnet connection is created.  The shell thread
+      is started with stdin, stdout, and stderror mapped to the TTY device.
+    * netutils/telnetd:  The old uIP telnet demo is gone.  In its place is a new
+      telnet infrastructure. The new telnet daemon creates sessions that are
+      &quot;wrapped&quot; as character devices and mapped to stdin, stdout, and stderr.
+      Now the telnet session can be inherited by spawned tasks.
+    * examples/telnetd:  Add a test for the new telnet daemon.
+    * examples/telnetd/telnetd_driver.c: Move the internal socket structure from
+      the daemon's socket array into the driver's state data so that it will be
+      independent from the the telnetd daemon.
+    * apps/system/readline:  Moved the old nuttx/lib/stdio/lib_fgets.c here
+      and renamed it as readline().  The old fgets was simplied and the overloaded
+      readline functionality was removed.
+    * apps/netutils/ftpd:  Add an FTPD server (does not even compile on initial
+      checkin).
+    * apps/examples/ftpd:  Add a test for the FTPD server (untest on initial
+      check-in).pascal-3.1 2012-xx-xx Gregory Nutt &lt;gnutt@nuttx.org&gt;
 
 buildroot-1.11 2012-xx-xx &lt;gnutt@nuttx.org&gt;
 
diff --git a/nuttx/configs/stm3210e-eval/src/up_adc.c b/nuttx/configs/stm3210e-eval/src/up_adc.c
index 6b1a8cb50e..c7c7e0c0a4 100644
--- a/nuttx/configs/stm3210e-eval/src/up_adc.c
+++ b/nuttx/configs/stm3210e-eval/src/up_adc.c
@@ -57,8 +57,7 @@
 /************************************************************************************
  * Definitions
  ************************************************************************************/
-
-/* Configuration ************************************************************/
+/* Configuration ********************************************************************/
 /* Up to 3 ADC interfaces are supported */
 
 #if STM32_NADC < 3
diff --git a/nuttx/drivers/Makefile b/nuttx/drivers/Makefile
index 9d804871e9..332233d521 100644
--- a/nuttx/drivers/Makefile
+++ b/nuttx/drivers/Makefile
@@ -70,6 +70,10 @@ ifneq ($(CONFIG_DISABLE_MOUNTPOINT),y)
   CSRCS += ramdisk.c rwbuffer.c
 endif
 
+ifeq ($(CONFIG_RAMLOG),y)
+  CSRCS += ramlog.c
+endif
+
 ifeq ($(CONFIG_CAN),y)
   CSRCS += can.c
 endif
diff --git a/nuttx/drivers/README.txt b/nuttx/drivers/README.txt
index e5a1483b22..0cddb93115 100644
--- a/nuttx/drivers/README.txt
+++ b/nuttx/drivers/README.txt
@@ -31,6 +31,19 @@ ramdisk.c
 	a block driver that can be mounted as a files system.  See
 	include/nuttx/ramdisk.h.
 
+ramlog.c
+	This is a driver that was intended to support debugging output,
+	aka syslogging, when the normal serial output is not available.
+	For example, if you are using a telnet or USB serial console,
+	the debug output will get lost.
+
+	This driver is similar to a pipe in that it saves the debugging
+	output in a FIFO in RAM.  It differs from a pipe in numerous
+	details as needed to support logging.
+
+	This driver is built when CONFIG_RAMLOG is defined in the Nuttx
+	configuration.
+
 rwbuffer.c
 	A facility that can be use by any block driver in-order to add
 	writing buffering and read-ahead buffering.
diff --git a/nuttx/drivers/ramlog.c b/nuttx/drivers/ramlog.c
new file mode 100644
index 0000000000..79f57636cd
--- /dev/null
+++ b/nuttx/drivers/ramlog.c
@@ -0,0 +1,590 @@
+/****************************************************************************
+ * drivers/ramlog.c
+ *
+ *   Copyright (C) 2012 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 <stdbool.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <string.h>
+#include <poll.h>
+#include <errno.h>
+#include <assert.h>
+#include <debug.h>
+
+#include <nuttx/fs.h>
+#include <nuttx/kmalloc.h>
+#include <nuttx/fs.h>
+#include <nuttx/arch.h>
+//#include <nuttx/ramlog.h>
+
+#include <arch/irq.h>
+
+#ifdef CONFIG_RAMLOG
+
+/****************************************************************************
+ * Private Types
+ ****************************************************************************/
+/* Configuration ************************************************************/
+/* CONFIG_RAMLOG - Enables the RAM logging feature
+ * CONFIG_RAMLOG_CONSOLE - Use the RAM logging device as a system console.
+ * CONFIG_RAMLOG_SYSLOG - Use the RAM logging device for the syslogging
+ *   interface.  This should have:
+ *   CONFIG_SYSLOG=ramlog
+ * CONFIG_RAMLOG_NPOLLWAITERS - The number of threads than can be waiting
+ *   for this driver on poll().  Default: 4
+ */
+
+#ifndef CONFIG_RAMLOG_NPOLLWAITERS
+#  define CONFIG_RAMLOG_NPOLLWAITERS 4
+#endif
+
+#ifndef CONFIG_SYSLOG
+#  undef CONFIG_RAMLOG_SYSLOG
+#endif
+
+/****************************************************************************
+ * Private Types
+ ****************************************************************************/
+
+struct ramlog_dev_s
+{
+  volatile uint8_t  rl_nwaiters;     /* Number of threads waiting for data */
+  volatile uint16_t rl_head;         /* The head index (where data is added) */
+  volatile uint16_t rl_tail;         /* The tail index (where data is remove) */
+  sem_t             rl_exclsem;      /* Enforces mutually exclusive access */
+  sem_t             rl_waitsem;      /* Used to wait for data */
+  size_t            rl_bufsize;      /* Size of the RAM buffer */
+  FAR char         *rl_buffer;       /* Circular RAM buffer */
+
+  /* The following is a list if poll structures of threads waiting for
+   * driver events. The 'struct pollfd' reference for each open is also
+   * retained in the f_priv field of the 'struct file'.
+   */
+
+#ifndef CONFIG_DISABLE_POLL
+  struct pollfd *rl_fds[CONFIG_RAMLOG_NPOLLWAITERS];
+#endif
+};
+
+/****************************************************************************
+ * Private Function Prototypes
+ ****************************************************************************/
+
+static ssize_t ramlog_read(FAR struct file *, FAR char *, size_t);
+static ssize_t ramlog_write(FAR struct file *, FAR const char *, size_t);
+#ifndef CONFIG_DISABLE_POLL
+static int     ramlog_poll(FAR struct file *filep, FAR struct pollfd *fds,
+                           bool setup);
+#endif
+
+/****************************************************************************
+ * Private Data
+ ****************************************************************************/
+
+static const struct file_operations g_ramlogfops =
+{
+  0,             /* open */
+  0,             /* close */
+  ramlog_read,   /* read */
+  ramlog_write,  /* write */
+  0,             /* seek */
+  0              /* ioctl */
+#ifndef CONFIG_DISABLE_POLL
+  , ramlog_poll  /* poll */
+#endif
+};
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: ramlog_pollnotify
+ ****************************************************************************/
+
+#ifndef CONFIG_DISABLE_POLL
+static void ramlog_pollnotify(FAR struct ramlog_dev_s *priv, pollevent_t eventset)
+{
+  FAR struct pollfd *fds;
+  irqstate_t flags;
+  int i;
+
+  /* This function may be called from an interrupt handler */
+
+  for (i = 0; i < CONFIG_RAMLOG_NPOLLWAITERS; i++)
+    {
+      flags = irqsave();
+      fds = priv->rl_fds[i];
+      if (fds)
+        {
+          fds->revents |= (fds->events & eventset);
+          if (fds->revents != 0)
+            {
+              sem_post(fds->sem);
+            }
+        }
+      irqrestore(flags);
+    }
+}
+#else
+#  define ramlog_pollnotify(priv,event)
+#endif
+
+/****************************************************************************
+ * Name: ramlog_read
+ ****************************************************************************/
+
+static ssize_t ramlog_read(FAR struct file *filep, FAR char *buffer, size_t len)
+{
+  struct inode *inode  = filep->f_inode;
+  struct ramlog_dev_s *priv;
+  ssize_t nread;
+  char ch;
+  int ret;
+
+  /* Some sanity checking */
+
+  DEBUGASSERT(inode && inode->i_private);
+  priv = inode->i_private;
+
+  /* If the circular buffer is empty, then wait for something to be written
+   * to it.  This function may NOT be called from an interrupt handler.
+   */
+
+  DEBUGASSERT(!up_interrupt_context());
+
+  /* Get exclusive access to the rl_tail index */
+
+  ret = sem_wait(&priv->rl_exclsem);
+  if (ret < 0)
+    {
+      return ret;
+    }
+
+  /* Loop until something is read */
+
+  for (nread = 0; nread < len; )
+    {
+      /* Get the next byte from the buffer */
+
+      if (priv->rl_head == priv->rl_tail)
+        {
+          /* The circular buffer is empty.  Did we read anything? */
+
+          if (nread > 0)
+            {
+              /* Yes.. re-enable interrupts and the break out to return what
+               * we have.
+               */
+
+              break;
+            }
+
+          /* If the driver was opened with O_NONBLOCK option, then don't wait.
+           * Re-enable interrupts and return EGAIN.
+           */
+
+          if (filep->f_oflags & O_NONBLOCK)
+            {
+              nread = -EAGAIN;
+              break;
+            }
+
+          /* Otherwise, wait for something to be written to the circular
+           * buffer. Increment the number of waiters so that the ramlog_write()
+           * will not that it needs to post the semaphore to wake us up.
+           */
+
+          sched_lock();
+          priv->rl_nwaiters++;
+          sem_post(&priv->rl_exclsem);
+
+          /* We may now be pre-empted!  But that should be okay because we
+           * have already incremented nwaiters.  Pre-emptions is disabled
+           * but will be re-enabled while we are waiting.
+           */
+
+          ret = sem_wait(&priv->rl_waitsem);
+
+          /* Interrupts will be disabled when we return.  So the decrementing
+           * rl_nwaiters here is safe.
+           */
+
+          priv->rl_nwaiters--;
+          sched_unlock();
+
+          /* Did we successfully get the rl_waitsem? */
+
+          if (ret >= 0)
+            {
+              /* Yes... then retake the mutual exclusion semaphore */
+
+              ret = sem_wait(&priv->rl_exclsem);
+            }
+
+          /* Was the semaphore wait successful? Did we successful re-take the
+           * mutual exclusion semaphore?
+           */
+
+          if (ret < 0) 
+            {
+              /* No.. One of the two sem_wait's failed. */
+
+              int errval = errno;
+
+              /* Were we awakened by a signal?  Did we read anything before
+               * we received the signal?
+               */
+
+              if (errval != EINTR || nread >= 0)
+                {
+                  /* Yes.. return the error. */
+
+                  nread = -errval;
+                }
+
+              /* Break out to return what we have.  Note, we can't exactly
+               * "break" out because whichever error occurred, we do not hold
+               * the exclusion semaphore.
+               */
+
+              goto errout_without_sem;
+            }
+        }
+      else
+        {
+          /* The circular buffer is not empty, get the next byte from the
+           * tail index.
+           */
+
+          ch = priv->rl_buffer[priv->rl_tail];
+
+          /* Increment the tail index and re-enable interrupts */
+
+          if (++priv->rl_tail >= priv->rl_bufsize)
+            {
+              priv->rl_tail = 0;
+            }
+
+          /* Add the character to the user buffer */
+
+          buffer[nread] = ch;
+          nread++;
+        }
+    }
+
+  /* Relinquish the mutual exclusion semaphore */
+
+  sem_post(&priv->rl_exclsem);
+
+  /* Notify all poll/select waiters that they can write to the FIFO */
+
+errout_without_sem:
+  if (nread > 0)
+    {
+      ramlog_pollnotify(priv, POLLOUT);
+    }
+  return nread;
+}
+
+/****************************************************************************
+ * Name: ramlog_write
+ ****************************************************************************/
+
+static ssize_t ramlog_write(FAR struct file *filep, FAR const char *buffer, size_t len)
+{
+  struct inode *inode = filep->f_inode;
+  struct ramlog_dev_s *priv;
+  irqstate_t flags;
+  ssize_t nwritten;
+  int nexthead;
+  int i;
+
+  /* Some sanity checking */
+
+  DEBUGASSERT(inode && inode->i_private);
+  priv = inode->i_private;
+
+ /* Loop until all of the bytes have been written.  This function may be
+  * called from an interrupt handler!  Semaphores cannot be used!
+  *
+  * The write logic only needs to modify the rl_head index.  Therefore,
+  * there is a difference in the way that rl_head and rl_tail are protected:
+  * rl_tail is protected with a semaphore; rl_tail is protected by disabling
+  * interrupts.
+  */
+
+  for (nwritten = 0; nwritten < len; nwritten++)
+    {
+      /* Disable interrupts (in case we are NOT called from interrupt handler) */
+
+      flags = irqsave();
+
+      /* Calculate the write index AFTER the next byte is written */
+
+      nexthead = priv->rl_head + 1;
+      if (nexthead >= priv->rl_bufsize)
+        {
+          nexthead = 0;
+        }
+
+      /* Would the next write overflow the circular buffer? */
+
+      if (nexthead == priv->rl_tail)
+        {
+          /* Yes... then break out of the loop to return the number of bytes
+           * written.  The data to be written is dropped on the floor.
+           */
+
+          return nwritten;
+        }
+
+      /* No... copy the byte and re-enable interrupts */
+
+      priv->rl_buffer[priv->rl_head] = buffer[nwritten];
+      priv->rl_head = nexthead;
+      irqrestore(flags);
+    }
+
+  /* Was anything written? */
+
+  if (nwritten > 0)
+    {
+      /* Are there threads waiting for read data? */
+
+      flags = irqsave();
+      for (i = 0; i < priv->rl_nwaiters; i++)
+        {
+          /* Yes.. Notify all of the waiting readers that more data is available */
+
+          sem_post(&priv->rl_waitsem);
+        }
+
+      /* Notify all poll/select waiters that they can write to the FIFO */
+
+      ramlog_pollnotify(priv, POLLIN);
+    }
+ 
+  /* Return the number of bytes written */
+
+  return nwritten;
+}
+
+/****************************************************************************
+ * Name: ramlog_poll
+ ****************************************************************************/
+
+#ifndef CONFIG_DISABLE_POLL
+int ramlog_poll(FAR struct file *filep, FAR struct pollfd *fds, bool setup)
+{
+  FAR struct inode *inode = filep->f_inode;
+  FAR struct ramlog_dev_s *priv;
+  pollevent_t eventset;
+  int ndx;
+  int ret;
+  int i;
+
+  /* Some sanity checking */
+
+  DEBUGASSERT(inode && inode->i_private);
+  priv = inode->i_private;
+
+  /* Get exclusive access to the poll structures */
+
+  ret = sem_wait(&priv->rl_exclsem);
+  if (ret < 0)
+    {
+      int errval = errno;
+      return -errval;
+    }
+
+  /* Are we setting up the poll?  Or tearing it down? */
+
+  if (setup)
+    {
+      /* This is a request to set up the poll.  Find an available
+       * slot for the poll structure reference
+       */
+
+      for (i = 0; i < CONFIG_RAMLOG_NPOLLWAITERS; i++)
+        {
+          /* Find an available slot */
+
+          if (!priv->rl_fds[i])
+            {
+              /* Bind the poll structure and this slot */
+
+              priv->rl_fds[i] = fds;
+              fds->priv       = &priv->rl_fds[i];
+              break;
+            }
+        }
+
+      if (i >= CONFIG_RAMLOG_NPOLLWAITERS)
+        {
+          fds->priv    = NULL;
+          ret          = -EBUSY;
+          goto errout;
+        }
+
+      /* Should immediately notify on any of the requested events?
+       * First, check if the xmit buffer is full.
+       */
+
+      eventset = 0;
+
+      ndx = priv->rl_head + 1;
+      if (ndx >= priv->rl_bufsize)
+        {
+          ndx = 0;
+        }
+  
+      if (ndx != priv->rl_tail)
+       {
+         eventset |= POLLOUT;
+       }
+
+      /* Check if the receive buffer is empty */
+
+      if (priv->rl_head != priv->rl_tail)
+       {
+         eventset |= POLLIN;
+       }
+
+      if (eventset)
+        {
+          ramlog_pollnotify(priv, eventset);
+        }
+
+    }
+  else if (fds->priv)
+    {
+      /* This is a request to tear down the poll. */
+
+      struct pollfd **slot = (struct pollfd **)fds->priv;
+
+#ifdef CONFIG_DEBUG
+      if (!slot)
+        {
+          ret = -EIO;
+          goto errout;
+        }
+#endif
+
+      /* Remove all memory of the poll setup */
+
+      *slot      = NULL;
+      fds->priv  = NULL;
+    }
+
+errout:
+  sem_post(&priv->rl_exclsem);
+  return ret;
+}
+#endif
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: ramlog_register
+ *
+ * Description:
+ *   Create the RAM logging device and register it at the specified path.
+ *   Mostly likely this path will be /dev/console
+ *
+ ****************************************************************************/
+
+int ramlog_register(FAR const char *devpath, FAR char *buffer, size_t buflen)
+{
+  FAR struct ramlog_dev_s *priv;
+  int ret = -ENOMEM;
+
+  /* Sanity checking */
+
+  DEBUGASSERT(devpath && buffer && buflen > 1);
+
+  /* Allocate a RAM logging device structure */
+
+  priv = (struct ramlog_dev_s *)kzalloc(sizeof(struct ramlog_dev_s));
+  if (priv)
+    {
+      /* Initialize the non-zero values in the RAM logging device structure */
+
+      sem_init(&priv->rl_exclsem, 0, 1);
+      sem_init(&priv->rl_waitsem, 0, 0);
+      priv->rl_bufsize = buflen;
+      priv->rl_buffer  = buffer;
+
+      /* Register the character driver */
+
+      ret = register_driver(devpath, &g_ramlogfops, 0666, priv);
+      if (ret < 0)
+        {
+          kfree(priv);
+        }
+    }
+
+  return ret;
+}
+
+/****************************************************************************
+ * Name: ramlog
+ *
+ * Description:
+ *   This is the low-level system logging interface.  The debugging/syslogging
+ *   interfaces are lib_rawprintf() and lib_lowprinf().  The difference is
+ *   the lib_rawprintf() writes to fd=1 (stdout) and lib_lowprintf() uses
+ *   a lower level interface that works from interrupt handlers.  This
+ *   function is a a low-level interface used to implement lib_lowprintf()
+ *   when CONFIG_RAMLOG_SYSLOG=y and CONFIG_SYSLOG=ramlog
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_RAMLOG_SYSLOG
+#  warning "Missing logic"
+#endif
+
+#endif /* CONFIG_RAMLOG */