Completes coding of the PWM module

git-svn-id: https://nuttx.svn.sourceforge.net/svnroot/nuttx/trunk@4200 7fd9a85b-ad96-42d3-883c-3090e2eb8679

5 files changed, 2294 insertions, 0 deletions

diff --git a/nuttx/drivers/serial/Make.defs b/nuttx/drivers/serial/Make.defs
new file mode 100644
index 000000000..b78628334
--- /dev/null
+++ b/nuttx/drivers/serial/Make.defs
@@ -0,0 +1,50 @@
+############################################################################
+# drivers/serial/Make.defs
+#
+#   Copyright (C) 2009, 2011 Gregory Nutt. All rights reserved.
+#   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
+#
+# 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.
+#
+############################################################################
+
+ifneq ($(CONFIG_NFILE_DESCRIPTORS),0)
+
+# Include serial drivers
+
+CSRCS += serial.c serialirq.c lowconsole.c
+
+ifeq ($(CONFIG_16550_UART),y)
+  CSRCS += uart_16550.c
+endif
+
+# Include serial build support
+
+DEPPATH += --dep-path serial
+VPATH += :serial
+endif
diff --git a/nuttx/drivers/serial/lowconsole.c b/nuttx/drivers/serial/lowconsole.c
new file mode 100644
index 000000000..1de76cc06
--- /dev/null
+++ b/nuttx/drivers/serial/lowconsole.c
@@ -0,0 +1,132 @@
+/****************************************************************************
+ * drivers/serial/lowconsole.c
+ *
+ *   Copyright (C) 2008, 2009 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
+ *
+ * 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 <errno.h>
+#include <debug.h>
+
+#include <nuttx/arch.h>
+#include <nuttx/fs.h>
+
+/****************************************************************************
+ * Definitions
+ ****************************************************************************/
+
+/* The architecture must provide up_putc for this driver */
+
+#ifndef CONFIG_ARCH_LOWPUTC
+#  error "Architecture must provide up_putc() for this driver"
+#endif
+
+/****************************************************************************
+ * Private Function Prototypes
+ ****************************************************************************/
+
+static ssize_t lowconsole_read(struct file *filep, char *buffer, size_t buflen);
+static ssize_t lowconsole_write(struct file *filep, const char *buffer, size_t buflen);
+static int     lowconsole_ioctl(struct file *filep, int cmd, unsigned long arg);
+
+/****************************************************************************
+ * Private Variables
+ ****************************************************************************/
+
+static const struct file_operations g_consoleops =
+{
+  0,                /* open */
+  0,                /* close */
+  lowconsole_read,  /* read */
+  lowconsole_write, /* write */
+  0,                /* seek */
+  lowconsole_ioctl  /* ioctl */
+#ifndef CONFIG_DISABLE_POLL
+  , 0               /* poll */
+#endif
+};
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: lowconsole_ioctl
+ ****************************************************************************/
+
+static int lowconsole_ioctl(struct file *filep, int cmd, unsigned long arg)
+{
+  return -ENOTTY;
+}
+
+/****************************************************************************
+ * Name: lowconsole_read
+ ****************************************************************************/
+
+static ssize_t lowconsole_read(struct file *filep, char *buffer, size_t buflen)
+{
+  return 0;
+}
+
+/****************************************************************************
+ * Name: lowconsole_write
+ ****************************************************************************/
+
+static ssize_t lowconsole_write(struct file *filep, const char *buffer, size_t buflen)
+{
+  ssize_t ret = buflen;
+ 
+  for (; buflen; buflen--)
+    {
+      up_putc(*buffer++);
+    }
+  return ret;
+}
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: lowconsole_init
+****************************************************************************/
+
+void lowconsole_init(void)
+{
+  (void)register_driver("/dev/console", &g_consoleops, 0666, NULL);
+}
diff --git a/nuttx/drivers/serial/serial.c b/nuttx/drivers/serial/serial.c
new file mode 100644
index 000000000..cff810743
--- /dev/null
+++ b/nuttx/drivers/serial/serial.c
@@ -0,0 +1,763 @@
+/************************************************************************************
+ * drivers/serial/serial.c
+ *
+ *   Copyright (C) 2007-2009, 2011 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
+ *
+ * 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 <unistd.h>
+#include <semaphore.h>
+#include <string.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <errno.h>
+#include <debug.h>
+
+#include <nuttx/irq.h>
+#include <nuttx/arch.h>
+#include <nuttx/fs.h>
+#include <nuttx/serial.h>
+
+/************************************************************************************
+ * Definitions
+ ************************************************************************************/
+
+/* The architecture must provide up_putc for this driver */
+
+#ifndef CONFIG_ARCH_LOWPUTC
+#  error "Architecture must provide up_putc() for this driver"
+#endif
+
+#define uart_putc(ch) up_putc(ch)
+
+#define HALF_SECOND_MSEC 500
+#define HALF_SECOND_USEC 500000L
+
+/************************************************************************************
+ * Private Types
+ ************************************************************************************/
+
+/************************************************************************************
+ * Private Function Prototypes
+ ************************************************************************************/
+
+static int     uart_open(FAR struct file *filep);
+static int     uart_close(FAR struct file *filep);
+static ssize_t uart_read(FAR struct file *filep, FAR char *buffer, size_t buflen);
+static ssize_t uart_write(FAR struct file *filep, FAR const char *buffer, size_t buflen);
+static int     uart_ioctl(FAR struct file *filep, int cmd, unsigned long arg);
+#ifndef CONFIG_DISABLE_POLL
+static int     uart_poll(FAR struct file *filep, FAR struct pollfd *fds, bool setup);
+#endif
+
+/************************************************************************************
+ * Private Variables
+ ************************************************************************************/
+
+static const struct file_operations g_serialops =
+{
+  uart_open,  /* open */
+  uart_close, /* close */
+  uart_read,  /* read */
+  uart_write, /* write */
+  0,          /* seek */
+  uart_ioctl  /* ioctl */
+#ifndef CONFIG_DISABLE_POLL
+  , uart_poll /* poll */
+#endif
+};
+
+/************************************************************************************
+ * Private Functions
+ ************************************************************************************/
+
+/************************************************************************************
+ * Name: uart_takesem
+ ************************************************************************************/
+
+static void uart_takesem(FAR sem_t *sem)
+{
+  while (sem_wait(sem) != 0)
+    {
+      /* The only case that an error should occur here is if
+       * the wait was awakened by a signal.
+       */
+
+      ASSERT(*get_errno_ptr() == EINTR);
+    }
+}
+
+/************************************************************************************
+ * Name: uart_givesem
+ ************************************************************************************/
+
+#define uart_givesem(sem) (void)sem_post(sem)
+
+/****************************************************************************
+ * Name: uart_pollnotify
+ ****************************************************************************/
+
+#ifndef CONFIG_DISABLE_POLL
+static void uart_pollnotify(FAR uart_dev_t *dev, pollevent_t eventset)
+{
+  int i;
+
+  for (i = 0; i < CONFIG_DEV_CONSOLE_NPOLLWAITERS; i++)
+    {
+      struct pollfd *fds = dev->fds[i];
+      if (fds)
+        {
+          fds->revents |= (fds->events & eventset);
+          if (fds->revents != 0)
+            {
+              fvdbg("Report events: %02x\n", fds->revents);
+              sem_post(fds->sem);
+            }
+        }
+    }
+}
+#else
+#  define uart_pollnotify(dev,event)
+#endif
+
+/************************************************************************************
+ * Name: uart_putxmitchar
+ ************************************************************************************/
+
+static void uart_putxmitchar(FAR uart_dev_t *dev, int ch)
+{
+  irqstate_t flags;
+  int nexthead;
+
+  /* Increment to see what the next head pointer will be.  We need to use the "next"
+   * head pointer to determine when the circular buffer would overrun
+   */
+ 
+  nexthead = dev->xmit.head + 1;
+  if (nexthead >= dev->xmit.size)
+    {
+      nexthead = 0;
+    }
+
+  /* Loop until we are able to add the character to the TX buffer */
+  
+  for (;;)
+    {
+      if (nexthead != dev->xmit.tail)
+        {
+          dev->xmit.buffer[dev->xmit.head] = ch;
+          dev->xmit.head = nexthead;
+          return;
+        }
+      else
+        {
+          /* Inform the interrupt level logic that we are waiting.
+           * This and the following steps must be atomic.
+           */
+
+          flags = irqsave();
+          dev->xmitwaiting = true;
+
+          /* Wait for some characters to be sent from the buffer
+           * with the TX interrupt enabled.  When the TX interrupt
+           * is enabled, uart_xmitchars should execute and remove
+           * some of the data from the TX buffer.
+           */
+
+          uart_enabletxint(dev);
+          uart_takesem(&dev->xmitsem);
+          uart_disabletxint(dev);
+          irqrestore(flags);
+        }
+    }
+}
+
+/************************************************************************************
+ * Name: uart_irqwrite
+ ************************************************************************************/
+
+static ssize_t uart_irqwrite(FAR uart_dev_t *dev, FAR const char *buffer, size_t buflen)
+{
+  ssize_t ret = buflen;
+
+  /* Force each character through the low level interface */
+
+  for (; buflen; buflen--)
+    {
+      int ch = *buffer++;
+      uart_putc(ch);
+
+     /* If this is the console, then we should replace LF with LF-CR */
+
+      if (ch == '\n')
+        {
+          uart_putc('\r');
+        }
+    }
+
+  return ret;
+}
+
+/************************************************************************************
+ * Name: uart_write
+ ************************************************************************************/
+
+static ssize_t uart_write(FAR struct file *filep, FAR const char *buffer, size_t buflen)
+{
+  FAR struct inode *inode = filep->f_inode;
+  FAR uart_dev_t   *dev   = inode->i_private;
+  ssize_t           ret   = buflen;
+
+  /* We may receive console writes through this path from
+   * interrupt handlers and from debug output in the IDLE task!
+   * In these cases, we will need to do things a little
+   * differently.
+   */
+
+  if (up_interrupt_context() || getpid() == 0)
+    {
+      if (dev->isconsole)
+        {
+          irqstate_t flags = irqsave();
+          ret = uart_irqwrite(dev, buffer, buflen);
+          irqrestore(flags);
+          return ret;
+        }
+      else
+        {
+          return ERROR;
+        }
+    }
+
+  /* Only one user can be accessing dev->xmit.head at once */
+
+  uart_takesem(&dev->xmit.sem);
+
+  /* Loop while we still have data to copy to the transmit buffer.
+   * we add data to the head of the buffer; uart_xmitchars takes the
+   * data from the end of the buffer.
+   */
+
+  uart_disabletxint(dev);
+  for (; buflen; buflen--)
+    {
+      int ch = *buffer++;
+
+      /* Put the character into the transmit buffer */
+
+      uart_putxmitchar(dev, ch);
+
+      /* If this is the console, then we should replace LF with LF-CR */
+
+      if (dev->isconsole && ch == '\n')
+        {
+          uart_putxmitchar(dev, '\r');
+        }
+    }
+
+  if (dev->xmit.head != dev->xmit.tail)
+    {
+      uart_enabletxint(dev);
+    }
+
+  uart_givesem(&dev->xmit.sem);
+  return ret;
+}
+
+/************************************************************************************
+ * Name: uart_read
+ ************************************************************************************/
+
+static ssize_t uart_read(FAR struct file *filep, FAR char *buffer, size_t buflen)
+{
+  FAR struct inode *inode = filep->f_inode;
+  FAR uart_dev_t   *dev   = inode->i_private;
+  irqstate_t        flags;
+  ssize_t           recvd = 0;
+
+  /* Only one user can be accessing dev->recv.tail at once */
+
+  uart_takesem(&dev->recv.sem);
+
+  /* Loop while we still have data to copy to the receive buffer.
+   * we add data to the head of the buffer; uart_xmitchars takes the
+   * data from the end of the buffer.
+   */
+
+  uart_disablerxint(dev);
+  while (recvd < buflen)
+    {
+      /* Check if there is more data to return in the circular buffer */
+
+      if (dev->recv.head != dev->recv.tail)
+        {
+          *buffer++ = dev->recv.buffer[dev->recv.tail];
+          recvd++;
+
+          if (++(dev->recv.tail) >= dev->recv.size)
+            {
+              dev->recv.tail = 0;
+            }
+        }
+
+#ifdef CONFIG_DEV_SERIAL_FULLBLOCKS
+      /* No... then we would have to wait to get receive more data.
+       * If the user has specified the O_NONBLOCK option, then just
+       * return what we have.
+       */
+
+      else if (filep->f_oflags & O_NONBLOCK)
+        {
+          /* If nothing was transferred, then return the -EAGAIN
+           * error (not zero which means end of file).
+           */
+
+          if (recvd < 1)
+            {
+              recvd = -EAGAIN;
+            }
+          break;
+       }
+#else
+      /* No... the circular buffer is empty.  Have we returned anything
+       * to the caller?
+       */
+
+      else if (recvd > 0)
+       {
+          /* Yes.. break out of the loop and return the number of bytes
+           * received up to the wait condition.
+           */
+
+          break;
+       }
+
+      /* No... then we would have to wait to get receive some data.
+       * If the user has specified the O_NONBLOCK option, then do not
+       * wait.
+       */
+
+      else if (filep->f_oflags & O_NONBLOCK)
+        {
+          /* Break out of the loop returning -EAGAIN */
+
+          recvd = -EAGAIN;
+          break;
+        }
+#endif
+      /* Otherwise we are going to have to wait for data to arrive */
+
+      else
+        {
+          /* Wait for some characters to be sent from the buffer with the RX interrupt
+           * re-enabled.  Interrupts are disabled briefly to assure that the following
+           * operations are atomic.
+           */
+
+          flags = irqsave();
+          dev->recvwaiting = true;
+          uart_enablerxint(dev);
+          uart_takesem(&dev->recvsem);
+          uart_disablerxint(dev);
+          irqrestore(flags);
+        }
+    }
+
+  uart_enablerxint(dev);
+  uart_givesem(&dev->recv.sem);
+  return recvd;
+}
+
+/************************************************************************************
+ * Name: uart_ioctl
+ ************************************************************************************/
+
+static int uart_ioctl(FAR struct file *filep, int cmd, unsigned long arg)
+{
+  FAR struct inode *inode = filep->f_inode;
+  FAR uart_dev_t   *dev   = inode->i_private;
+
+  return dev->ops->ioctl(filep, cmd, arg);
+}
+
+/****************************************************************************
+ * Name: uart_poll
+ ****************************************************************************/
+
+#ifndef CONFIG_DISABLE_POLL
+int uart_poll(FAR struct file *filep, FAR struct pollfd *fds, bool setup)
+{
+  FAR struct inode *inode = filep->f_inode;
+  FAR uart_dev_t   *dev   = inode->i_private;
+  pollevent_t       eventset;
+  int               ndx;
+  int               ret   = OK;
+  int               i;
+
+  /* Some sanity checking */
+
+#if CONFIG_DEBUG
+  if (!dev || !fds)
+    {
+      return -ENODEV;
+    }
+#endif
+
+  /* Are we setting up the poll?  Or tearing it down? */
+
+  uart_takesem(&dev->pollsem);
+  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_DEV_CONSOLE_NPOLLWAITERS; i++)
+        {
+          /* Find an available slot */
+
+          if (!dev->fds[i])
+            {
+              /* Bind the poll structure and this slot */
+
+              dev->fds[i]  = fds;
+              fds->priv    = &dev->fds[i];
+              break;
+            }
+        }
+
+      if (i >= CONFIG_DEV_CONSOLE_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;
+
+      uart_takesem(&dev->xmit.sem);
+      ndx = dev->xmit.head + 1;
+      if (ndx >= dev->xmit.size)
+        {
+          ndx = 0;
+        }
+      if (ndx != dev->xmit.tail)
+       {
+         eventset |= POLLOUT;
+       }
+      uart_givesem(&dev->xmit.sem);
+
+      /* Check if the receive buffer is empty */
+
+      uart_takesem(&dev->recv.sem);
+      if (dev->recv.head != dev->recv.tail)
+       {
+         eventset |= POLLIN;
+       }
+      uart_givesem(&dev->recv.sem);
+
+      if (eventset)
+        {
+          uart_pollnotify(dev, 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:
+  uart_givesem(&dev->pollsem);
+  return ret;
+}
+#endif
+
+/************************************************************************************
+ * Name: uart_close
+ *
+ * Description:
+ *   This routine is called when the serial port gets closed.
+ *   It waits for the last remaining data to be sent.
+ *
+ ************************************************************************************/
+
+static int uart_close(FAR struct file *filep)
+{
+  FAR struct inode *inode = filep->f_inode;
+  FAR uart_dev_t   *dev   = inode->i_private;
+  irqstate_t        flags;
+
+  uart_takesem(&dev->closesem);
+  if (dev->open_count > 1)
+    {
+      dev->open_count--;
+      uart_givesem(&dev->closesem);
+      return OK;
+    }
+
+  /* There are no more references to the port */
+
+  dev->open_count = 0;
+
+  /* Stop accepting input */
+
+  uart_disablerxint(dev);
+
+  /* Now we wait for the transmit buffer to clear */
+
+  while (dev->xmit.head != dev->xmit.tail)
+    {
+#ifndef CONFIG_DISABLE_SIGNALS
+      usleep(HALF_SECOND_USEC);
+#else
+      up_mdelay(HALF_SECOND_MSEC);
+#endif
+    }
+
+  /* And wait for the TX fifo to drain */
+
+  while (!uart_txempty(dev))
+    {
+#ifndef CONFIG_DISABLE_SIGNALS
+      usleep(HALF_SECOND_USEC);
+#else
+      up_mdelay(HALF_SECOND_MSEC);
+#endif
+    }
+
+  /* Free the IRQ and disable the UART */
+
+  flags = irqsave();       /* Disable interrupts */
+  uart_detach(dev);        /* Detach interrupts */
+  if (!dev->isconsole)     /* Check for the serial console UART */
+    {
+      uart_shutdown(dev);  /* Disable the UART */
+    }
+  irqrestore(flags);
+
+  uart_givesem(&dev->closesem);
+  return OK;
+ }
+
+/************************************************************************************
+ * Name: uart_open
+ *
+ * Description:
+ *   This routine is called whenever a serial port is opened.
+ *
+ ************************************************************************************/
+
+static int uart_open(FAR struct file *filep)
+{
+  struct inode *inode = filep->f_inode;
+  uart_dev_t   *dev   = inode->i_private;
+  uint8_t       tmp;
+  int           ret   = OK;
+
+  /* If the port is the middle of closing, wait until the close is finished */
+
+  uart_takesem(&dev->closesem);
+
+  /* Start up serial port */
+  /* Increment the count of references to the device. */
+
+  tmp = dev->open_count + 1;
+  if (tmp == 0)
+    {
+      /* More than 255 opens; uint8_t overflows to zero */
+
+      ret = -EMFILE;
+      goto errout_with_sem;
+    }
+
+  /* Check if this is the first time that the driver has been opened. */
+
+  if (tmp == 1)
+    {
+      irqstate_t flags = irqsave();
+
+      /* If this is the console, then the UART has already been initialized. */
+
+      if (!dev->isconsole)
+        {
+          /* Perform one time hardware initialization */
+
+          ret = uart_setup(dev);
+          if (ret < 0)
+            {
+              irqrestore(flags);
+              goto errout_with_sem;
+            }
+        }
+
+      /* In any event, we do have to configure for interrupt driven mode of
+       * operation.  Attach the hardware IRQ(s). Hmm.. should shutdown() the
+       * the device in the rare case that uart_attach() fails, tmp==1, and
+       * this is not the console.
+       */
+
+      ret = uart_attach(dev);
+      if (ret < 0)
+        {
+           uart_shutdown(dev);
+           irqrestore(flags);
+           goto errout_with_sem;
+        }
+
+      /* Mark the io buffers empty */
+
+      dev->xmit.head = 0;
+      dev->xmit.tail = 0;
+      dev->recv.head = 0;
+      dev->recv.tail = 0;
+
+      /* Enable the RX interrupt */
+
+      uart_enablerxint(dev);
+      irqrestore(flags);
+    }
+
+  /* Save the new open count on success */
+
+  dev->open_count = tmp;
+
+errout_with_sem:
+  uart_givesem(&dev->closesem);
+  return ret;
+}
+
+/************************************************************************************
+ * Public Functions
+ ************************************************************************************/
+
+/************************************************************************************
+ * Name: uart_register
+ *
+ * Description:
+ *   Register serial console and serial ports.
+ *
+ ************************************************************************************/
+
+int uart_register(FAR const char *path, FAR uart_dev_t *dev)
+{
+  sem_init(&dev->xmit.sem, 0, 1);
+  sem_init(&dev->recv.sem, 0, 1);
+  sem_init(&dev->closesem, 0, 1);
+  sem_init(&dev->xmitsem,  0, 0);
+  sem_init(&dev->recvsem,  0, 0);
+#ifndef CONFIG_DISABLE_POLL
+  sem_init(&dev->pollsem,  0, 1);
+#endif
+
+  dbg("Registering %s\n", path);
+  return register_driver(path, &g_serialops, 0666, dev);
+}
+
+/************************************************************************************
+ * Name: uart_datareceived
+ *
+ * Description:
+ *   This function is called from uart_recvchars when new serial data is place in 
+ *   the driver's circular buffer.  This function will wake-up any stalled read()
+ *   operations that are waiting for incoming data.
+ *
+ ************************************************************************************/
+
+void uart_datareceived(FAR uart_dev_t *dev)
+{
+  /* Awaken any awaiting read() operations */
+
+  if (dev->recvwaiting)
+    {
+      dev->recvwaiting = false;
+      (void)sem_post(&dev->recvsem);
+    }
+
+  /* Notify all poll/select waiters that they can read from the recv buffer */
+
+  uart_pollnotify(dev, POLLIN);
+
+}
+
+/************************************************************************************
+ * Name: uart_datasent
+ *
+ * Description:
+ *   This function is called from uart_xmitchars after serial data has been sent,
+ *   freeing up some space in the driver's circular buffer. This function will
+ *   wake-up any stalled write() operations that was waiting for space to buffer
+ *   outgoing data.
+ *
+ ************************************************************************************/
+
+void uart_datasent(FAR uart_dev_t *dev)
+{
+  if (dev->xmitwaiting)
+    {
+      dev->xmitwaiting = false;
+      (void)sem_post(&dev->xmitsem);
+    }
+
+  /* Notify all poll/select waiters that they can write to xmit buffer */
+
+  uart_pollnotify(dev, POLLOUT);
+}
+
+
diff --git a/nuttx/drivers/serial/serialirq.c b/nuttx/drivers/serial/serialirq.c
new file mode 100644
index 000000000..22af6896f
--- /dev/null
+++ b/nuttx/drivers/serial/serialirq.c
@@ -0,0 +1,187 @@
+/************************************************************************************
+ * drivers/serial/serialirq.c
+ *
+ *   Copyright (C) 2007-2009, 2011 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
+ *
+ * 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 <semaphore.h>
+#include <debug.h>
+#include <nuttx/serial.h>
+
+/************************************************************************************
+ * Pre-processor Definitions
+ ************************************************************************************/
+
+/************************************************************************************
+ * Private Types
+ ************************************************************************************/
+
+/************************************************************************************
+ * Private Function Prototypes
+ ************************************************************************************/
+
+/************************************************************************************
+ * Private Variables
+ ************************************************************************************/
+
+/************************************************************************************
+ * Private Functions
+ ************************************************************************************/
+
+/************************************************************************************
+ * Public Functions
+ ************************************************************************************/
+
+/************************************************************************************
+ * Name: uart_xmitchars
+ *
+ * Description:
+ *   This function is called from the UART interrupt handler when an interrupt
+ *   is received indicating that there is more space in the transmit FIFO.  This
+ *   function will send characters from the tail of the xmit buffer while the driver
+ *   write() logic adds data to the head of the xmit buffer.
+ *
+ ************************************************************************************/
+
+void uart_xmitchars(FAR uart_dev_t *dev)
+{
+  uint16_t nbytes = 0;
+
+  /* Send while we still have data & room in the fifo */
+
+  while (dev->xmit.head != dev->xmit.tail && uart_txready(dev))
+    {
+      /* Send the next byte */
+
+      uart_send(dev, dev->xmit.buffer[dev->xmit.tail]);
+      nbytes++;
+
+      /* Increment the tail index */
+
+      if (++(dev->xmit.tail) >= dev->xmit.size)
+        {
+          dev->xmit.tail = 0;
+        }
+    }
+
+  /* When all of the characters have been sent from the buffer disable the TX
+   * interrupt.
+   */
+
+  if (dev->xmit.head == dev->xmit.tail)
+    {
+      uart_disabletxint(dev);
+    }
+
+  /* If any bytes were removed from the buffer, inform any waiters there there is
+   * space available.
+   */
+
+  if (nbytes)
+    {
+      uart_datasent(dev);
+    }
+}
+
+/************************************************************************************
+ * Name: uart_receivechars
+ *
+ * Description:
+ *   This function is called from the UART interrupt handler when an interrupt
+ *   is received indicating that are bytes available in the receive fifo.  This
+ *   function will add chars to head of receive buffer.  Driver read() logic will
+ *   take characters from the tail of the buffer.
+ *
+ ************************************************************************************/
+
+void uart_recvchars(FAR uart_dev_t *dev)
+{
+  unsigned int status;
+  int nexthead = dev->recv.head + 1;
+  uint16_t nbytes = 0;
+
+  if (nexthead >= dev->recv.size)
+    {
+      nexthead = 0;
+    }
+
+  /* Loop putting characters into the receive buffer until either there are no
+   * further characters to available.
+   */
+
+  while (uart_rxavailable(dev))
+    {
+      char ch =  uart_receive(dev, &status);
+      
+      /* If the RX buffer becomes full, then the serial data is discarded.  This is
+       * necessary because on most serial hardware, you must read the data in order
+       * to clear the RX interrupt. An option on some hardware might be to simply
+       * disable RX interrupts until the RX buffer becomes non-FULL.  However, that
+       * would probably just cause the overrun to occur in hardware (unless it has
+       * some large internal buffering).
+       */
+
+      if (nexthead != dev->recv.tail)
+        {
+          /* Add the character to the buffer */
+
+          dev->recv.buffer[dev->recv.head] = ch;
+          nbytes++;
+
+          /* Increment the head index */
+
+          dev->recv.head = nexthead;
+          if (++nexthead >= dev->recv.size)
+            {
+               nexthead = 0;
+            }
+        }
+    }
+
+  /* If any bytes were added to the buffer, inform any waiters there there is new
+   * incoming data available.
+   */
+
+  if (nbytes)
+    {
+      uart_datareceived(dev);
+    }
+}
+
diff --git a/nuttx/drivers/serial/uart_16550.c b/nuttx/drivers/serial/uart_16550.c
new file mode 100644
index 000000000..07c0dae36
--- /dev/null
+++ b/nuttx/drivers/serial/uart_16550.c
@@ -0,0 +1,1162 @@
+/****************************************************************************
+ * drivers/serial/uart_16550.c
+ * Serial driver for 16550 UART
+ *
+ *   Copyright (C) 2011 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
+ *
+ * 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 <unistd.h>
+#include <semaphore.h>
+#include <string.h>
+#include <errno.h>
+#include <debug.h>
+
+#include <nuttx/irq.h>
+#include <nuttx/arch.h>
+#include <nuttx/serial.h>
+#include <nuttx/ioctl.h>
+#include <nuttx/uart_16550.h>
+
+#include <arch/board/board.h>
+
+#ifdef CONFIG_16550_UART
+
+/****************************************************************************
+ * Pre-processor definitions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Types
+ ****************************************************************************/
+
+struct u16550_s
+{
+  uart_addrwidth_t uartbase;  /* Base address of UART registers */
+#ifndef CONFIG_16550_SUPRESS_CONFIG
+  uint32_t         baud;      /* Configured baud */
+  uint32_t         uartclk;   /* UART clock frequency */
+#endif
+#ifndef CONFIG_SUPPRESS_SERIAL_INTS
+  uart_datawidth_t ier;       /* Saved IER value */
+  uint8_t          irq;       /* IRQ associated with this UART */
+#endif
+#ifndef CONFIG_16550_SUPRESS_CONFIG
+  uint8_t          parity;    /* 0=none, 1=odd, 2=even */
+  uint8_t          bits;      /* Number of bits (7 or 8) */
+  bool             stopbits2; /* true: Configure with 2 stop bits instead of 1 */
+#endif
+};
+
+/****************************************************************************
+ * Private Function Prototypes
+ ****************************************************************************/
+
+static int  u16550_setup(struct uart_dev_s *dev);
+static void u16550_shutdown(struct uart_dev_s *dev);
+static int  u16550_attach(struct uart_dev_s *dev);
+static void u16550_detach(struct uart_dev_s *dev);
+#ifndef CONFIG_SUPPRESS_SERIAL_INTS
+static int  u16550_interrupt(int irq, void *context);
+#endif
+static int  u16550_ioctl(struct file *filep, int cmd, unsigned long arg);
+static int  u16550_receive(struct uart_dev_s *dev, uint32_t *status);
+static void u16550_rxint(struct uart_dev_s *dev, bool enable);
+static bool u16550_rxavailable(struct uart_dev_s *dev);
+static void u16550_send(struct uart_dev_s *dev, int ch);
+static void u16550_txint(struct uart_dev_s *dev, bool enable);
+static bool u16550_txready(struct uart_dev_s *dev);
+static bool u16550_txempty(struct uart_dev_s *dev);
+
+/****************************************************************************
+ * Private Variables
+ ****************************************************************************/
+
+struct uart_ops_s g_uart_ops =
+{
+  .setup          = u16550_setup,
+  .shutdown       = u16550_shutdown,
+  .attach         = u16550_attach,
+  .detach         = u16550_detach,
+  .ioctl          = u16550_ioctl,
+  .receive        = u16550_receive,
+  .rxint          = u16550_rxint,
+  .rxavailable    = u16550_rxavailable,
+  .send           = u16550_send,
+  .txint          = u16550_txint,
+  .txready        = u16550_txready,
+  .txempty        = u16550_txempty,
+};
+
+/* I/O buffers */
+
+#ifdef CONFIG_16550_UART0
+static char g_uart0rxbuffer[CONFIG_UART0_RXBUFSIZE];
+static char g_uart0txbuffer[CONFIG_UART0_TXBUFSIZE];
+#endif
+#ifdef CONFIG_16550_UART1
+static char g_uart1rxbuffer[CONFIG_UART1_RXBUFSIZE];
+static char g_uart1txbuffer[CONFIG_UART1_TXBUFSIZE];
+#endif
+#ifdef CONFIG_16550_UART2
+static char g_uart2rxbuffer[CONFIG_UART1_RXBUFSIZE];
+static char g_uart2txbuffer[CONFIG_UART1_TXBUFSIZE];
+#endif
+#ifdef CONFIG_16550_UART3
+static char g_uart3rxbuffer[CONFIG_UART1_RXBUFSIZE];
+static char g_uart3txbuffer[CONFIG_UART1_TXBUFSIZE];
+#endif
+
+/* This describes the state of the LPC17xx uart0 port. */
+
+#ifdef CONFIG_16550_UART0
+static struct u16550_s g_uart0priv =
+{
+  .uartbase       = CONFIG_16550_UART0_BASE,
+#ifndef CONFIG_16550_SUPRESS_CONFIG
+  .baud           = CONFIG_UART0_BAUD,
+  .uartclk        = CONFIG_16550_UART0_CLOCK,
+#endif
+#ifndef CONFIG_SUPPRESS_SERIAL_INTS
+  .irq            = CONFIG_16550_UART0_IRQ,
+#endif
+#ifndef CONFIG_16550_SUPRESS_CONFIG
+  .parity         = CONFIG_UART0_PARITY,
+  .bits           = CONFIG_UART0_BITS,
+  .stopbits2      = CONFIG_UART0_2STOP,
+#endif
+};
+
+static uart_dev_t g_uart0port =
+{
+  .recv     =
+  {
+    .size   = CONFIG_UART0_RXBUFSIZE,
+    .buffer = g_uart0rxbuffer,
+  },
+  .xmit     =
+  {
+    .size   = CONFIG_UART0_TXBUFSIZE,
+    .buffer = g_uart0txbuffer,
+  },
+  .ops      = &g_uart_ops,
+  .priv     = &g_uart0priv,
+};
+#endif
+
+/* This describes the state of the LPC17xx uart1 port. */
+
+#ifdef CONFIG_16550_UART1
+static struct u16550_s g_uart1priv =
+{
+  .uartbase       = CONFIG_16550_UART1_BASE,
+#ifndef CONFIG_16550_SUPRESS_CONFIG
+  .baud           = CONFIG_UART1_BAUD,
+  .uartclk        = CONFIG_16550_UART1_CLOCK,
+#endif
+#ifndef CONFIG_SUPPRESS_SERIAL_INTS
+  .irq            = CONFIG_16550_UART1_IRQ,
+#endif
+#ifndef CONFIG_16550_SUPRESS_CONFIG
+  .parity         = CONFIG_UART1_PARITY,
+  .bits           = CONFIG_UART1_BITS,
+  .stopbits2      = CONFIG_UART1_2STOP,
+#endif
+};
+
+static uart_dev_t g_uart1port =
+{
+  .recv     =
+  {
+    .size   = CONFIG_UART1_RXBUFSIZE,
+    .buffer = g_uart1rxbuffer,
+  },
+  .xmit     =
+  {
+    .size   = CONFIG_UART1_TXBUFSIZE,
+    .buffer = g_uart1txbuffer,
+   },
+  .ops      = &g_uart_ops,
+  .priv     = &g_uart1priv,
+};
+#endif
+
+/* This describes the state of the LPC17xx uart1 port. */
+
+#ifdef CONFIG_16550_UART2
+static struct u16550_s g_uart2priv =
+{
+  .uartbase       = CONFIG_16550_UART2_BASE,
+#ifndef CONFIG_16550_SUPRESS_CONFIG
+  .baud           = CONFIG_UART2_BAUD,
+  .uartclk        = CONFIG_16550_UART2_CLOCK,
+#endif
+#ifndef CONFIG_SUPPRESS_SERIAL_INTS
+  .irq            = CONFIG_16550_UART2_IRQ,
+#endif
+#ifndef CONFIG_16550_SUPRESS_CONFIG
+  .parity         = CONFIG_UART2_PARITY,
+  .bits           = CONFIG_UART2_BITS,
+  .stopbits2      = CONFIG_UART2_2STOP,
+#endif
+};
+
+static uart_dev_t g_uart2port =
+{
+  .recv     =
+  {
+    .size   = CONFIG_UART2_RXBUFSIZE,
+    .buffer = g_uart2rxbuffer,
+  },
+  .xmit     =
+  {
+    .size   = CONFIG_UART2_TXBUFSIZE,
+    .buffer = g_uart2txbuffer,
+   },
+  .ops      = &g_uart_ops,
+  .priv     = &g_uart2priv,
+};
+#endif
+
+/* This describes the state of the LPC17xx uart1 port. */
+
+#ifdef CONFIG_16550_UART3
+static struct u16550_s g_uart3priv =
+{
+  .uartbase       = CONFIG_16550_UART3_BASE,
+#ifndef CONFIG_16550_SUPRESS_CONFIG
+  .baud           = CONFIG_UART3_BAUD,
+  .uartclk        = CONFIG_16550_UART3_CLOCK,
+#endif
+#ifndef CONFIG_SUPPRESS_SERIAL_INTS
+  .irq            = CONFIG_16550_UART3_IRQ,
+#endif
+#ifndef CONFIG_16550_SUPRESS_CONFIG
+  .parity         = CONFIG_UART3_PARITY,
+  .bits           = CONFIG_UART3_BITS,
+  .stopbits2      = CONFIG_UART3_2STOP,
+#endif
+};
+
+static uart_dev_t g_uart3port =
+{
+  .recv     =
+  {
+    .size   = CONFIG_UART3_RXBUFSIZE,
+    .buffer = g_uart3rxbuffer,
+  },
+  .xmit     =
+  {
+    .size   = CONFIG_UART3_TXBUFSIZE,
+    .buffer = g_uart3txbuffer,
+   },
+  .ops      = &g_uart_ops,
+  .priv     = &g_uart3priv,
+};
+#endif
+
+/* Which UART with be tty0/console and which tty1? tty2? tty3? */
+
+#if defined(CONFIG_UART0_SERIAL_CONSOLE)
+#  define CONSOLE_DEV     g_uart0port      /* UART0=console */
+#  define TTYS0_DEV       g_uart0port      /* UART0=ttyS0 */
+#  ifdef CONFIG_16550_UART1
+#    define TTYS1_DEV     g_uart1port      /* UART0=ttyS0;UART1=ttyS1 */
+#    ifdef CONFIG_16550_UART2
+#      define TTYS2_DEV   g_uart2port      /* UART0=ttyS0;UART1=ttyS1;UART2=ttyS2 */
+#      ifdef CONFIG_16550_UART3
+#        define TTYS3_DEV g_uart3port      /* UART0=ttyS0;UART1=ttyS1;UART2=ttyS2;UART3=ttyS3 */
+#      else
+#        undef TTYS3_DEV                   /* UART0=ttyS0;UART1=ttyS1;UART2=ttyS;No ttyS3 */
+#      endif
+#    else
+#      ifdef CONFIG_16550_UART3
+#        define TTYS2_DEV g_uart3port     /* UART0=ttyS0;UART1=ttyS1;UART3=ttys2;No ttyS3 */
+#      else
+#        undef TTYS2_DEV                  /* UART0=ttyS0;UART1=ttyS1;No ttyS2;No ttyS3 */
+#      endif
+#      undef TTYS3_DEV                    /* No ttyS3 */
+#    endif
+#  else
+#    ifdef CONFIG_16550_UART2
+#      define TTYS1_DEV   g_uart2port    /* UART0=ttyS0;UART2=ttyS1;No ttyS3 */
+#      ifdef CONFIG_16550_UART3
+#        define TTYS2_DEV g_uart3port    /* UART0=ttyS0;UART2=ttyS1;UART3=ttyS2;No ttyS3 */
+#      else
+#        undef TTYS2_DEV                 /* UART0=ttyS0;UART2=ttyS1;No ttyS2;No ttyS3 */
+#      endif
+#      undef TTYS3_DEV                   /* No ttyS3 */
+#    else
+#      ifdef CONFIG_16550_UART3
+#        define TTYS1_DEV g_uart3port    /* UART0=ttyS0;UART3=ttyS1;No ttyS2;No ttyS3 */
+#      else
+#        undef TTYS1_DEV                 /* UART0=ttyS0;No ttyS1;No ttyS2;No ttyS3 */
+#      endif
+#        undef TTYS2_DEV                  /* No ttyS2 */
+#      undef TTYS3_DEV                    /* No ttyS3 */
+#    endif
+#  endif
+#elif defined(CONFIG_UART1_SERIAL_CONSOLE)
+#  define CONSOLE_DEV     g_uart1port     /* UART1=console */
+#  define TTYS0_DEV       g_uart1port     /* UART1=ttyS0 */
+#  ifdef CONFIG_16550_UART
+#    define TTYS1_DEV     g_uart0port     /* UART1=ttyS0;UART0=ttyS1 */
+#    ifdef CONFIG_16550_UART2
+#      define TTYS2_DEV   g_uart2port     /* UART1=ttyS0;UART0=ttyS1;UART2=ttyS2 */
+#      ifdef CONFIG_16550_UART3
+#        define TTYS3_DEV g_uart3port     /* UART1=ttyS0;UART0=ttyS1;UART2=ttyS2;UART3=ttyS3 */
+#      else
+#        undef TTYS3_DEV                  /* UART1=ttyS0;UART0=ttyS1;UART2=ttyS;No ttyS3 */
+#      endif
+#    else
+#      ifdef CONFIG_16550_UART3
+#        define TTYS2_DEV g_uart3port     /* UART1=ttyS0;UART0=ttyS1;UART3=ttys2;No ttyS3 */
+#      else
+#        undef TTYS2_DEV                  /* UART1=ttyS0;UART0=ttyS1;No ttyS2;No ttyS3 */
+#      endif
+#      undef TTYS3_DEV                    /* No ttyS3 */
+#    endif
+#  else
+#    ifdef CONFIG_16550_UART2
+#      define TTYS1_DEV   g_uart2port     /* UART1=ttyS0;UART2=ttyS1 */
+#      ifdef CONFIG_16550_UART3
+#        define TTYS2_DEV g_uart3port     /* UART1=ttyS0;UART2=ttyS1;UART3=ttyS2;No ttyS3 */
+#      else
+#        undef TTYS2_DEV                  /* UART1=ttyS0;UART2=ttyS1;No ttyS2;No ttyS3 */
+#      endif
+#      undef TTYS3_DEV                    /* No ttyS3 */
+#    else
+#      ifdef CONFIG_16550_UART3
+#        define TTYS1_DEV   g_uart3port   /* UART1=ttyS0;UART3=ttyS1;No ttyS2;No ttyS3 */
+#      else
+#        undef TTYS1_DEV                  /* UART1=ttyS0;No ttyS1;No ttyS2;No ttyS3 */
+#      endif
+#      undef TTYS2_DEV                    /* No ttyS2 */
+#      undef TTYS3_DEV                    /* No ttyS3 */
+#    endif
+#  endif
+#elif defined(CONFIG_UART2_SERIAL_CONSOLE)
+#  define CONSOLE_DEV     g_uart2port     /* UART2=console */
+#  define TTYS0_DEV       g_uart2port     /* UART2=ttyS0 */
+#  ifdef CONFIG_16550_UART
+#    define TTYS1_DEV     g_uart0port     /* UART2=ttyS0;UART0=ttyS1 */
+#    ifdef CONFIG_16550_UART1
+#      define TTYS2_DEV   g_uart1port     /* UART2=ttyS0;UART0=ttyS1;UART1=ttyS2 */
+#      ifdef CONFIG_16550_UART3
+#        define TTYS3_DEV g_uart3port     /* UART2=ttyS0;UART0=ttyS1;UART1=ttyS2;UART3=ttyS3 */
+#      else
+#        undef TTYS3_DEV                  /* UART2=ttyS0;UART0=ttyS1;UART1=ttyS;No ttyS3 */
+#      endif
+#    else
+#      ifdef CONFIG_16550_UART3
+#        define TTYS2_DEV g_uart3port     /* UART2=ttyS0;UART0=ttyS1;UART3=ttys2;No ttyS3 */
+#      else
+#        undef TTYS2_DEV                  /* UART2=ttyS0;UART0=ttyS1;No ttyS2;No ttyS3 */
+#      endif
+#      undef TTYS3_DEV                    /* No ttyS3 */
+#    endif
+#  else
+#    ifdef CONFIG_16550_UART1
+#      define TTYS1_DEV   g_uart1port    /* UART2=ttyS0;UART1=ttyS1 */
+#      ifdef CONFIG_16550_UART3
+#        define TTYS2_DEV g_uart3port    /* UART2=ttyS0;UART1=ttyS1;UART3=ttyS2 */
+#      else
+#        undef TTYS2_DEV                 /* UART2=ttyS0;UART1=ttyS1;No ttyS2;No ttyS3 */
+#      endif
+#      undef TTYS3_DEV                   /* No ttyS3 */
+#    else
+#      ifdef CONFIG_16550_UART3
+#        define TTYS1_DEV g_uart3port    /* UART2=ttyS0;UART3=ttyS1;No ttyS3 */
+#      else
+#        undef TTYS1_DEV                 /* UART2=ttyS0;No ttyS1;No ttyS2;No ttyS3 */
+#      endif
+#      undef TTYS2_DEV                   /* No ttyS2 */
+#      undef TTYS3_DEV                   /* No ttyS3 */
+#    endif
+#  endif
+#elif defined(CONFIG_UART3_SERIAL_CONSOLE)
+#  define CONSOLE_DEV     g_uart3port    /* UART3=console */
+#  define TTYS0_DEV       g_uart3port    /* UART3=ttyS0 */
+#  ifdef CONFIG_16550_UART
+#    define TTYS1_DEV     g_uart0port    /* UART3=ttyS0;UART0=ttyS1 */
+#    ifdef CONFIG_16550_UART1
+#      define TTYS2_DEV   g_uart1port    /* UART3=ttyS0;UART0=ttyS1;UART1=ttyS2 */
+#      ifdef CONFIG_16550_UART2
+#        define TTYS3_DEV g_uart2port    /* UART3=ttyS0;UART0=ttyS1;UART1=ttyS2;UART2=ttyS3 */
+#      else
+#        undef TTYS3_DEV                 /* UART3=ttyS0;UART0=ttyS1;UART1=ttyS;No ttyS3 */
+#      endif
+#    else
+#      ifdef CONFIG_16550_UART2
+#        define TTYS2_DEV g_uart2port    /* UART3=ttyS0;UART0=ttyS1;UART2=ttys2;No ttyS3 */
+#      else
+#        undef TTYS2_DEV                 /* UART3=ttyS0;UART0=ttyS1;No ttyS2;No ttyS3 */
+#      endif
+#        undef TTYS3_DEV                 /* No ttyS3 */
+#    endif
+#  else
+#    ifdef CONFIG_16550_UART1
+#      define TTYS1_DEV   g_uart1port    /* UART3=ttyS0;UART1=ttyS1 */
+#      ifdef CONFIG_16550_UART2
+#        define TTYS2_DEV g_uart2port    /* UART3=ttyS0;UART1=ttyS1;UART2=ttyS2;No ttyS3 */
+#      else
+#        undef TTYS2_DEV                 /* UART3=ttyS0;UART1=ttyS1;No ttyS2;No ttyS3 */
+#      endif
+#      undef TTYS3_DEV                   /* No ttyS3 */
+#    else
+#      ifdef CONFIG_16550_UART2
+#        define TTYS1_DEV   g_uart2port  /* UART3=ttyS0;UART2=ttyS1;No ttyS3;No ttyS3 */
+#        undef TTYS3_DEV                 /* UART3=ttyS0;UART2=ttyS1;No ttyS2;No ttyS3 */
+#      else
+#        undef TTYS1_DEV                 /* UART3=ttyS0;No ttyS1;No ttyS2;No ttyS3 */
+#      endif
+#      undef TTYS2_DEV                   /* No ttyS2 */
+#      undef TTYS3_DEV                   /* No ttyS3 */
+#    endif
+#  endif
+#endif
+
+/************************************************************************************
+ * Inline Functions
+ ************************************************************************************/
+
+/****************************************************************************
+ * Name: u16550_serialin
+ ****************************************************************************/
+
+static inline uart_datawidth_t u16550_serialin(struct u16550_s *priv, int offset)
+{
+  return uart_getreg(priv->uartbase, offset);
+}
+
+/****************************************************************************
+ * Name: u16550_serialout
+ ****************************************************************************/
+
+static inline void u16550_serialout(struct u16550_s *priv, int offset, uart_datawidth_t value)
+{
+  uart_putreg(priv->uartbase, offset, value);
+}
+
+/****************************************************************************
+ * Name: u16550_disableuartint
+ ****************************************************************************/
+
+#ifndef CONFIG_SUPPRESS_SERIAL_INTS
+static inline void u16550_disableuartint(struct u16550_s *priv, uart_datawidth_t *ier)
+{
+  if (ier)
+    {
+      *ier = priv->ier & UART_IER_ALLIE;
+    }
+
+  priv->ier &= ~UART_IER_ALLIE;
+  u16550_serialout(priv, UART_IER_OFFSET, priv->ier);
+}
+#else
+#  define u16550_disableuartint(priv,ier)
+#endif
+
+/****************************************************************************
+ * Name: u16550_restoreuartint
+ ****************************************************************************/
+
+#ifndef CONFIG_SUPPRESS_SERIAL_INTS
+static inline void u16550_restoreuartint(struct u16550_s *priv, uint32_t ier)
+{
+  priv->ier |= ier & UART_IER_ALLIE;
+  u16550_serialout(priv, UART_IER_OFFSET, priv->ier);
+}
+#else
+#  define u16550_restoreuartint(priv,ier)
+#endif
+
+/****************************************************************************
+ * Name: u16550_enablebreaks
+ ****************************************************************************/
+
+static inline void u16550_enablebreaks(struct u16550_s *priv, bool enable)
+{
+  uint32_t lcr = u16550_serialin(priv, UART_LCR_OFFSET);
+  if (enable)
+    {
+      lcr |= UART_LCR_BRK;
+    }
+  else
+    {
+      lcr &= ~UART_LCR_BRK;
+    }
+  u16550_serialout(priv, UART_LCR_OFFSET, lcr);
+}
+
+/************************************************************************************
+ * Name: u16550_divisor
+ *
+ * Descrption:
+ *   Select a divider to produce the BAUD from the UART_CLK.
+ *
+ *     BAUD = UART_CLK / (16 * DL), or
+ *     DIV  = UART_CLK / BAUD / 16
+ *
+ *   Ignoring the fractional divider for now.
+ *
+ ************************************************************************************/
+
+#ifndef CONFIG_16550_SUPRESS_CONFIG
+static inline uint32_t u16550_divisor(struct u16550_s *priv)
+{
+  return (priv->uartclk + (priv->baud << 3)) / (priv->baud << 4);
+}
+#endif
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: u16550_setup
+ *
+ * Description:
+ *   Configure the UART baud, bits, parity, fifos, etc. This
+ *   method is called the first time that the serial port is
+ *   opened.
+ *
+ ****************************************************************************/
+
+static int u16550_setup(struct uart_dev_s *dev)
+{
+#ifndef CONFIG_16550_SUPRESS_CONFIG
+  struct u16550_s *priv = (struct u16550_s*)dev->priv;
+  uint16_t div;
+  uint32_t lcr;
+
+  /* Clear fifos */
+
+  u16550_serialout(priv, UART_FCR_OFFSET, (UART_FCR_RXRST|UART_FCR_TXRST));
+
+  /* Set trigger */
+
+  u16550_serialout(priv, UART_FCR_OFFSET, (UART_FCR_FIFOEN|UART_FCR_RXTRIGGER_8));
+
+  /* Set up the IER */
+
+#ifndef CONFIG_SUPPRESS_SERIAL_INTS
+  priv->ier = u16550_serialin(priv, UART_IER_OFFSET);
+#endif
+
+  /* Set up the LCR */
+
+  lcr = 0;
+  switch (priv->bits)
+    {
+      case 5 :
+        lcr |= UART_LCR_WLS_7BIT;
+        break;
+
+      case 6 :
+        lcr |= UART_LCR_WLS_7BIT;
+        break;
+
+      case 7 :
+        lcr |= UART_LCR_WLS_7BIT;
+        break;
+
+      default:
+      case 8 :
+        lcr |= UART_LCR_WLS_7BIT;
+        break;
+    }
+
+  if (priv->stopbits2)
+    {
+      lcr |= UART_LCR_STB;
+    }
+
+  if (priv->parity == 1)
+    {
+      lcr |= UART_LCR_PEN;
+    }
+  else if (priv->parity == 2)
+    {
+      lcr |= (UART_LCR_PEN|UART_LCR_EPS);
+    }
+
+  /* Enter DLAB=1 */
+
+  u16550_serialout(priv, UART_LCR_OFFSET, (lcr | UART_LCR_DLAB));
+
+  /* Set the BAUD divisor */
+
+  div = u16550_divisor(priv);
+  u16550_serialout(priv, UART_DLM_OFFSET, div >> 8);
+  u16550_serialout(priv, UART_DLL_OFFSET, div & 0xff);
+
+  /* Clear DLAB */
+
+  u16550_serialout(priv, UART_LCR_OFFSET, lcr);
+
+  /* Configure the FIFOs */
+
+  u16550_serialout(priv, UART_FCR_OFFSET,
+                   (UART_FCR_RXTRIGGER_8|UART_FCR_TXRST|UART_FCR_RXRST|UART_FCR_FIFOEN));
+#endif
+  return OK;
+}
+
+/****************************************************************************
+ * Name: u16550_shutdown
+ *
+ * Description:
+ *   Disable the UART.  This method is called when the serial
+ *   port is closed
+ *
+ ****************************************************************************/
+
+static void u16550_shutdown(struct uart_dev_s *dev)
+{
+  struct u16550_s *priv = (struct u16550_s*)dev->priv;
+  u16550_disableuartint(priv, NULL);
+}
+
+/****************************************************************************
+ * Name: u16550_attach
+ *
+ * Description:
+ *   Configure the UART to operation in interrupt driven mode.  This method is
+ *   called when the serial port is opened.  Normally, this is just after the
+ *   the setup() method is called, however, the serial console may operate in
+ *   a non-interrupt driven mode during the boot phase.
+ *
+ *   RX and TX interrupts are not enabled when by the attach method (unless the
+ *   hardware supports multiple levels of interrupt enabling).  The RX and TX
+ *   interrupts are not enabled until the txint() and rxint() methods are called.
+ *
+ ****************************************************************************/
+
+static int u16550_attach(struct uart_dev_s *dev)
+{
+#ifndef CONFIG_SUPPRESS_SERIAL_INTS
+  struct u16550_s *priv = (struct u16550_s*)dev->priv;
+  int ret;
+
+  /* Attach and enable the IRQ */
+
+  ret = irq_attach(priv->irq, u16550_interrupt);
+#ifndef CONFIG_ARCH_NOINTC
+  if (ret == OK)
+    {
+       /* Enable the interrupt (RX and TX interrupts are still disabled
+        * in the UART
+        */
+
+       up_enable_irq(priv->irq);
+    }
+#endif
+  return ret;
+#else
+  return OK;
+#endif
+}
+
+/****************************************************************************
+ * Name: u16550_detach
+ *
+ * Description:
+ *   Detach UART interrupts.  This method is called when the serial port is
+ *   closed normally just before the shutdown method is called.  The exception is
+ *   the serial console which is never shutdown.
+ *
+ ****************************************************************************/
+
+static void u16550_detach(struct uart_dev_s *dev)
+{
+#ifndef CONFIG_SUPPRESS_SERIAL_INTS
+ struct u16550_s *priv = (struct u16550_s*)dev->priv;
+#ifndef CONFIG_ARCH_NOINTC
+  up_disable_irq(priv->irq);
+#endif
+  irq_detach(priv->irq);
+#endif
+}
+
+/****************************************************************************
+ * Name: u16550_interrupt
+ *
+ * Description:
+ *   This is the UART interrupt handler.  It will be invoked when an
+ *   interrupt received on the 'irq'  It should call uart_transmitchars or
+ *   uart_receivechar to perform the appropriate data transfers.  The
+ *   interrupt handling logic must be able to map the 'irq' number into the
+ *   appropriate u16550_s structure in order to call these functions.
+ *
+ ****************************************************************************/
+
+#ifndef CONFIG_SUPPRESS_SERIAL_INTS
+static int u16550_interrupt(int irq, void *context)
+{
+  struct uart_dev_s *dev = NULL;
+  struct u16550_s   *priv;
+  uint32_t           status;
+  int                passes;
+
+#ifdef CONFIG_16550_UART0
+  if (g_uart0priv.irq == irq)
+    {
+      dev = &g_uart0port;
+    }
+  else
+#endif
+#ifdef CONFIG_16550_UART1
+  if (g_uart1priv.irq == irq)
+    {
+      dev = &g_uart1port;
+    }
+  else
+#endif
+#ifdef CONFIG_16550_UART2
+  if (g_uart2priv.irq == irq)
+    {
+      dev = &g_uart2port;
+    }
+  else
+#endif
+#ifdef CONFIG_16550_UART3
+  if (g_uart3priv.irq == irq)
+    {
+      dev = &g_uart3port;
+    }
+#endif
+  ASSERT(dev != NULL);
+  priv = (struct u16550_s*)dev->priv;
+
+  /* Loop until there are no characters to be transferred or,
+   * until we have been looping for a long time.
+   */
+
+  for (passes = 0; passes < 256; passes++)
+    {
+      /* Get the current UART status and check for loop
+       * termination conditions
+       */
+
+       status = u16550_serialin(priv, UART_IIR_OFFSET);
+
+      /* The UART_IIR_INTSTATUS bit should be zero if there are pending
+       * interrupts
+       */
+
+      if ((status & UART_IIR_INTSTATUS) != 0)
+        {
+          /* Break out of the loop when there is no longer a
+           * pending interrupt
+           */
+
+          break;
+        }
+
+      /* Handle the interrupt by its interrupt ID field */
+
+      switch (status & UART_IIR_INTID_MASK)
+        {
+          /* Handle incoming, receive bytes (with or without timeout) */
+
+          case UART_IIR_INTID_RDA:
+          case UART_IIR_INTID_CTI:
+            {
+              uart_recvchars(dev);
+              break;
+            }
+
+          /* Handle outgoing, transmit bytes */
+
+          case UART_IIR_INTID_THRE:
+            {
+              uart_xmitchars(dev);
+              break;
+            }
+
+          /* Just clear modem status interrupts (UART1 only) */
+
+          case UART_IIR_INTID_MSI:
+            {
+              /* Read the modem status register (MSR) to clear */
+
+              status = u16550_serialin(priv, UART_MSR_OFFSET);
+              vdbg("MSR: %02x\n", status);
+              break;
+            }
+
+          /* Just clear any line status interrupts */
+
+          case UART_IIR_INTID_RLS:
+            {
+              /* Read the line status register (LSR) to clear */
+
+              status = u16550_serialin(priv, UART_LSR_OFFSET);
+              vdbg("LSR: %02x\n", status);
+              break;
+            }
+
+          /* There should be no other values */
+
+          default:
+            {
+              dbg("Unexpected IIR: %02x\n", status);
+              break;
+            }
+        }
+    }
+    return OK;
+}
+#endif
+
+/****************************************************************************
+ * Name: u16550_ioctl
+ *
+ * Description:
+ *   All ioctl calls will be routed through this method
+ *
+ ****************************************************************************/
+
+static int u16550_ioctl(struct file *filep, int cmd, unsigned long arg)
+{
+  struct inode      *inode = filep->f_inode;
+  struct uart_dev_s *dev   = inode->i_private;
+  struct u16550_s   *priv  = (struct u16550_s*)dev->priv;
+  int                ret   = OK;
+
+  switch (cmd)
+    {
+    case TIOCSERGSTRUCT:
+      {
+         struct u16550_s *user = (struct u16550_s*)arg;
+         if (!user)
+           {
+             *get_errno_ptr() = EINVAL;
+             ret = ERROR;
+           }
+         else
+           {
+             memcpy(user, dev, sizeof(struct u16550_s));
+           }
+       }
+       break;
+
+    case TIOCSBRK:  /* BSD compatibility: Turn break on, unconditionally */
+      {
+        irqstate_t flags = irqsave();
+        u16550_enablebreaks(priv, true);
+        irqrestore(flags);
+      }
+      break;
+
+    case TIOCCBRK:  /* BSD compatibility: Turn break off, unconditionally */
+      {
+        irqstate_t flags;
+        flags = irqsave();
+        u16550_enablebreaks(priv, false);
+        irqrestore(flags);
+      }
+      break;
+
+    default:
+      *get_errno_ptr() = ENOTTY;
+      ret = ERROR;
+      break;
+    }
+
+  return ret;
+}
+
+/****************************************************************************
+ * Name: u16550_receive
+ *
+ * Description:
+ *   Called (usually) from the interrupt level to receive one
+ *   character from the UART.  Error bits associated with the
+ *   receipt are provided in the return 'status'.
+ *
+ ****************************************************************************/
+
+static int u16550_receive(struct uart_dev_s *dev, uint32_t *status)
+{
+  struct u16550_s *priv = (struct u16550_s*)dev->priv;
+  uint32_t rbr;
+
+  *status = u16550_serialin(priv, UART_LSR_OFFSET);
+  rbr     = u16550_serialin(priv, UART_RBR_OFFSET);
+  return rbr;
+}
+
+/****************************************************************************
+ * Name: u16550_rxint
+ *
+ * Description:
+ *   Call to enable or disable RX interrupts
+ *
+ ****************************************************************************/
+
+static void u16550_rxint(struct uart_dev_s *dev, bool enable)
+{
+#ifndef CONFIG_SUPPRESS_SERIAL_INTS
+  struct u16550_s *priv = (struct u16550_s*)dev->priv;
+  if (enable)
+    {
+      priv->ier |= UART_IER_ERBFI;
+    }
+  else
+    {
+      priv->ier &= ~UART_IER_ERBFI;
+    }
+  u16550_serialout(priv, UART_IER_OFFSET, priv->ier);
+#endif
+}
+
+/****************************************************************************
+ * Name: u16550_rxavailable
+ *
+ * Description:
+ *   Return true if the receive fifo is not empty
+ *
+ ****************************************************************************/
+
+static bool u16550_rxavailable(struct uart_dev_s *dev)
+{
+  struct u16550_s *priv = (struct u16550_s*)dev->priv;
+  return ((u16550_serialin(priv, UART_LSR_OFFSET) & UART_LSR_DR) != 0);
+}
+
+/****************************************************************************
+ * Name: u16550_send
+ *
+ * Description:
+ *   This method will send one byte on the UART
+ *
+ ****************************************************************************/
+
+static void u16550_send(struct uart_dev_s *dev, int ch)
+{
+  struct u16550_s *priv = (struct u16550_s*)dev->priv;
+  u16550_serialout(priv, UART_THR_OFFSET, (uart_datawidth_t)ch);
+}
+
+/****************************************************************************
+ * Name: u16550_txint
+ *
+ * Description:
+ *   Call to enable or disable TX interrupts
+ *
+ ****************************************************************************/
+
+static void u16550_txint(struct uart_dev_s *dev, bool enable)
+{
+#ifndef CONFIG_SUPPRESS_SERIAL_INTS
+  struct u16550_s *priv = (struct u16550_s*)dev->priv;
+  irqstate_t flags;
+
+  flags = irqsave();
+  if (enable)
+    {
+      priv->ier |= UART_IER_ETBEI;
+      u16550_serialout(priv, UART_IER_OFFSET, priv->ier);
+
+      /* Fake a TX interrupt here by just calling uart_xmitchars() with
+       * interrupts disabled (note this may recurse).
+       */
+
+      uart_xmitchars(dev);
+    }
+  else
+    {
+      priv->ier &= ~UART_IER_ETBEI;
+      u16550_serialout(priv, UART_IER_OFFSET, priv->ier);
+    }
+  irqrestore(flags);
+#endif
+}
+
+/****************************************************************************
+ * Name: u16550_txready
+ *
+ * Description:
+ *   Return true if the tranmsit fifo is not full
+ *
+ ****************************************************************************/
+
+static bool u16550_txready(struct uart_dev_s *dev)
+{
+  struct u16550_s *priv = (struct u16550_s*)dev->priv;
+  return ((u16550_serialin(priv, UART_LSR_OFFSET) & UART_LSR_THRE) != 0);
+}
+
+/****************************************************************************
+ * Name: u16550_txempty
+ *
+ * Description:
+ *   Return true if the transmit fifo is empty
+ *
+ ****************************************************************************/
+
+static bool u16550_txempty(struct uart_dev_s *dev)
+{
+  struct u16550_s *priv = (struct u16550_s*)dev->priv;
+  return ((u16550_serialin(priv, UART_LSR_OFFSET) & UART_LSR_THRE) != 0);
+}
+
+/****************************************************************************
+ * Name: u16550_putc
+ *
+ * Description:
+ *   Write one character to the UART (polled)
+ *
+ ****************************************************************************/
+
+static void u16550_putc(struct u16550_s *priv, int ch)
+{
+  while ((u16550_serialin(priv, UART_LSR_OFFSET) & UART_LSR_THRE) != 0);
+  u16550_serialout(priv, UART_THR_OFFSET, (uart_datawidth_t)ch);
+}
+
+/****************************************************************************
+ * Public Funtions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: up_earlyserialinit
+ *
+ * Description:
+ *   Performs the low level UART initialization early in debug so that the
+ *   serial console will be available during bootup.  This must be called
+ *   before uart_serialinit.
+ *
+ *   NOTE: Configuration of the CONSOLE UART was performed by uart_lowsetup()
+ *   very early in the boot sequence.
+ *
+ ****************************************************************************/
+
+void up_earlyserialinit(void)
+{
+  /* Configure all UARTs (except the CONSOLE UART) and disable interrupts */
+
+#ifdef CONFIG_16550_UART0
+  u16550_disableuartint(&g_uart0priv, NULL);
+#endif
+#ifdef CONFIG_16550_UART1
+  u16550_disableuartint(&g_uart1priv, NULL);
+#endif
+#ifdef CONFIG_16550_UART2
+  u16550_disableuartint(&g_uart2priv, NULL);
+#endif
+#ifdef CONFIG_16550_UART3
+  u16550_disableuartint(&g_uart3priv, NULL);
+#endif
+
+  /* Configuration whichever one is the console */
+
+#ifdef CONSOLE_DEV
+  CONSOLE_DEV.isconsole = true;
+  u16550_setup(&CONSOLE_DEV);
+#endif
+}
+
+/****************************************************************************
+ * Name: up_serialinit
+ *
+ * Description:
+ *   Register serial console and serial ports.  This assumes that
+ *   up_earlyserialinit was called previously.
+ *
+ ****************************************************************************/
+
+void up_serialinit(void)
+{
+#ifdef CONSOLE_DEV
+  (void)uart_register("/dev/console", &CONSOLE_DEV);
+#endif
+#ifdef TTYS0_DEV
+  (void)uart_register("/dev/ttyS0", &TTYS0_DEV);
+#endif
+#ifdef TTYS1_DEV
+  (void)uart_register("/dev/ttyS1", &TTYS1_DEV);
+#endif
+#ifdef TTYS2_DEV
+  (void)uart_register("/dev/ttyS2", &TTYS2_DEV);
+#endif
+#ifdef TTYS3_DEV
+  (void)uart_register("/dev/ttyS3", &TTYS3_DEV);
+#endif
+}
+
+/****************************************************************************
+ * Name: up_putc
+ *
+ * Description:
+ *   Provide priority, low-level access to support OS debug  writes
+ *
+ ****************************************************************************/
+
+#ifdef HAVE_16550_CONSOLE
+int up_putc(int ch)
+{
+  struct u16550_s *priv = (struct u16550_s*)CONSOLE_DEV.priv;
+#ifndef CONFIG_SUPPRESS_SERIAL_INTS
+  uart_datawidth_t ier;
+
+  u16550_disableuartint(priv, &ier);
+#endif
+
+  /* Check for LF */
+
+  if (ch == '\n')
+    {
+      /* Add CR */
+
+      u16550_putc(priv, '\r');
+    }
+
+  u16550_putc(priv, ch);
+#ifndef CONFIG_SUPPRESS_SERIAL_INTS
+  u16550_restoreuartint(priv, ier);
+#endif
+  return ch;
+}
+#endif
+
+#endif /* CONFIG_UART_16550 */