diff --git a/ports/arm/platforms/qemu_integratorcp/Makefile b/ports/arm/platforms/qemu_integratorcp/Makefile
index 7243d1c..6bfe97b 100644
--- a/ports/arm/platforms/qemu_integratorcp/Makefile
+++ b/ports/arm/platforms/qemu_integratorcp/Makefile
@@ -23,7 +23,7 @@ QEMU=qemu-system-arm
 BUILD_DIR=build
 
 # Platform-specific object files
-PLATFORM_OBJECTS = modules.o
+PLATFORM_OBJECTS = modules.o uart.o
 PLATFORM_ASM_OBJECTS = startup.o
 
 # Port-specific object files
diff --git a/ports/arm/platforms/qemu_integratorcp/uart.c b/ports/arm/platforms/qemu_integratorcp/uart.c
new file mode 100644
index 0000000..4773004
--- /dev/null
+++ b/ports/arm/platforms/qemu_integratorcp/uart.c
@@ -0,0 +1,220 @@
+/*
+ * Copyright (c) 2013, Kelvin Lawson. All rights reserved.
+ *
+ * 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. No personal names or organizations' names associated with the
+ *    Atomthreads project may be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE ATOMTHREADS PROJECT 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 PROJECT 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.
+ */
+
+
+/** 
+ * \file
+ * UART implementation for non-hosted compiler toolchains.
+ *
+ *
+ * Some toolchains may be semi-hosted and implement these automatically
+ * for use within QEMU.
+ */
+
+#include "atom.h"
+#include "atommutex.h"
+#include "atomport.h"
+#include "uart.h"
+
+
+/* Constants */
+
+/** UART0 registers base address */
+#define UART0_ADDR       0x16000000
+
+/** FR Register bits */
+#define UART_FR_RXFE     0x10
+#define UART_FR_TXFF     0x20
+
+/** UART register access macros */
+#define UART_DR(baseaddr) (*(unsigned int *)(baseaddr))
+#define UART_FR(baseaddr) (*(((unsigned int *)(baseaddr))+6))
+
+
+/* Local data */
+
+/*
+ * Semaphore for single-threaded access to UART device
+ */
+static ATOM_MUTEX uart_mutex;
+
+/*
+ * Initialised flag
+ */
+static int initialised = FALSE;
+
+
+/* Forward declarations */
+static int uart_init (void);
+
+
+/**
+ * \b uart_init
+ *
+ * Initialisation of UART driver. Creates a mutex that enforces
+ * single-threaded access to the UART. We poll register bits
+ * to check when space is available, which would not otherwise
+ * be thread-safe.
+ *
+ * @retval ATOM_OK Success
+ * @retval ATOM_ERROR Failed to create mutex
+ */
+static int uart_init (void)
+{
+    int status;
+
+    /* Check we are not already initialised */
+    if (initialised == FALSE)
+    {
+        /* Create a mutex for single-threaded UART access */
+        if (atomMutexCreate (&uart_mutex) != ATOM_OK)
+        {
+            /* Mutex creation failed */
+            status = ATOM_ERROR;
+        }
+        else
+        {
+            /* Success */
+            initialised = TRUE;
+            status = ATOM_OK;
+        }
+    }
+
+    /* Finished */
+    return (status);
+}
+
+
+/**
+ * \b uart_read
+ *
+ * Simple polled UART read.
+ *
+ * @param[in] ptr Pointer to receive buffer
+ * @param[in] len Max bytes to read
+ *
+ * @retval Number of bytes read
+ *
+ */
+int uart_read (char *ptr, int len)
+{
+    int todo = 0;
+
+    /* Check we are initialised */
+    if (initialised == FALSE)
+    {
+        uart_init();
+    }
+
+    /* Check parameters */
+    if ((ptr == NULL) || (len == 0))
+    {
+        return 0;
+    }
+
+    /* Block thread on private access to the UART */
+    if (atomMutexGet(&uart_mutex, 0) == ATOM_OK)
+    {
+        /* Wait for not-empty */
+        while(UART_FR(UART0_ADDR) & UART_FR_RXFE)
+            ;
+
+        /* Read first byte */
+        *ptr++ = UART_DR(UART0_ADDR);
+
+        /* Loop over remaining bytes until empty */
+        for (todo = 1; todo < len; todo++)
+        {
+            /* Quit if receive FIFO empty */
+            if(UART_FR(UART0_ADDR) & UART_FR_RXFE)
+            {
+                break;
+            }
+
+            /* Read next byte */
+            *ptr++ = UART_DR(UART0_ADDR);
+        }
+
+        /* Return mutex access */
+        atomMutexPut(&uart_mutex);
+    }
+
+    /* Return number of bytes read */
+    return todo;
+}
+
+
+/**
+ * \b uart_write
+ *
+ * Simple polled UART write.
+ *
+ * @param[in] ptr Pointer to write buffer
+ * @param[in] len Number of bytes to write
+ *
+ * @retval Number of bytes written
+ */
+int uart_write (const char *ptr, int len)
+{
+    int todo;
+
+    /* Check we are initialised */
+    if (initialised == FALSE)
+    {
+        uart_init();
+    }
+
+    /* Check parameters */
+    if ((ptr == NULL) || (len == 0))
+    {
+        return 0;
+    }
+
+    /* Block thread on private access to the UART */
+    if (atomMutexGet(&uart_mutex, 0) == ATOM_OK)
+    {
+        /* Loop through all bytes to write */
+        for (todo = 0; todo < len; todo++)
+        {
+            /* Wait for empty */
+            while(UART_FR(UART0_ADDR) & UART_FR_TXFF)
+                ;
+
+            /* Write byte to UART */
+            UART_DR(UART0_ADDR) = *ptr++;
+        }
+
+        /* Return mutex access */
+        atomMutexPut(&uart_mutex);
+    }
+
+    /* Return bytes-written count */
+    return len;
+}
+
diff --git a/ports/arm/platforms/qemu_integratorcp/uart.h b/ports/arm/platforms/qemu_integratorcp/uart.h
new file mode 100644
index 0000000..57018c4
--- /dev/null
+++ b/ports/arm/platforms/qemu_integratorcp/uart.h
@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2013, Kelvin Lawson. All rights reserved.
+ *
+ * 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. No personal names or organizations' names associated with the
+ *    Atomthreads project may be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE ATOMTHREADS PROJECT 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 PROJECT 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.
+ */
+
+#ifndef __ATOM_UART_H
+#define __ATOM_UART_H
+
+/* UART driver APIs */
+extern int uart_read (char *ptr, int len);
+extern int uart_write (const char *ptr, int len);
+
+#endif /* __ATOM_UART_H */
diff --git a/ports/arm/syscalls.c b/ports/arm/syscalls.c
index 16c6a19..5e4c08e 100644
--- a/ports/arm/syscalls.c
+++ b/ports/arm/syscalls.c
@@ -37,20 +37,20 @@
  * without newlib. Allows usage of printf() and friends as well as heap
  * allocation.
  *
+ * NOTE: Platform/BSP must implement uart_read() and uart_write().
+ *
+ * NOTE: Platform/BSP linker script must define "end" and "heap_top" which are
+ * the heap base and top respectively.
+ *
+ * No file table is implemented. All file read/write operations are carried
+ * out on the UART driver, regardless of file descriptor.
+ *
  * Mostly based on code from http://balau82.wordpress.com
  *
  */
 
 #include <sys/stat.h>
-
-enum {
- UART_FR_RXFE = 0x10,
- UART_FR_TXFF = 0x20,
- UART0_ADDR = 0x16000000,
-};
-
-#define UART_DR(baseaddr) (*(unsigned int *)(baseaddr))
-#define UART_FR(baseaddr) (*(((unsigned int *)(baseaddr))+6))
+#include "uart.h"
 
 
 /** 
@@ -70,7 +70,7 @@ extern int _write(int file, char *ptr, int len) __attribute__((weak));
 /**
  * \b _close
  *
- * Simple stub implementation.
+ * Simple stub implementation with no file table. All parameters ignored.
  *
  */
 int _close(int file)
@@ -82,11 +82,12 @@ int _close(int file)
 /**
  * \b _fstat
  *
- * Simple stub implementation.
+ * Simple stub implementation. Always return character device.
  *
  */
 int _fstat(int file, struct stat *st)
 {
+    /* Only UART supported, always return character-oriented device file */
     st->st_mode = S_IFCHR;
     return 0;
 }
@@ -95,7 +96,7 @@ int _fstat(int file, struct stat *st)
 /**
  * \b _isatty
  *
- * Simple stub implementation.
+ * Simple stub implementation. Only UART supported so TTY always true.
  *
  */
 int _isatty(int file)
@@ -107,7 +108,7 @@ int _isatty(int file)
 /**
  * \b _lseek
  *
- * Simple stub implementation.
+ * Simple stub implementation. All parameters ignored.
  *
  */
 int _lseek(int file, int ptr, int dir)
@@ -119,7 +120,7 @@ int _lseek(int file, int ptr, int dir)
 /**
  * \b _open
  *
- * Simple stub implementation.
+ * Simple stub implementation with no file table. All parameters ignored.
  *
  */
 int _open(const char *name, int flags, int mode)
@@ -131,58 +132,52 @@ int _open(const char *name, int flags, int mode)
 /**
  * \b _read
  *
- * Simple stub implementation.
+ * Simple read file implementation. Ignores file descriptor parameter
+ * and always reads from the UART driver.
  *
+ * @param[in] file File descriptor (parameter ignored)
+ * @param[in] ptr Pointer to receive buffer
+ * @param[in] len Max bytes to read
+ *
+ * @retval Number of bytes read
  */
 int _read(int file, char *ptr, int len)
 {
-    int todo;
-
-    if(len == 0)
-        return 0;
-
-    while(UART_FR(UART0_ADDR) & UART_FR_RXFE)
-        ;
-
-    *ptr++ = UART_DR(UART0_ADDR);
-    for (todo = 1; todo < len; todo++)
-    {
-        if(UART_FR(UART0_ADDR) & UART_FR_RXFE)
-        {
-            break;
-        }
-        *ptr++ = UART_DR(UART0_ADDR);
-    }
-    return todo;
+    /* Read from the UART driver, regardless of file descriptor */
+	return (uart_read (ptr, len));
 }
 
 
 /**
  * \b _write
  *
- * Simple stub implementation.
+ * Simple write file implementation. Ignores file descriptor parameter
+ * and always writes to the UART driver.
  *
+ * @param[in] file File descriptor (parameter ignored)
+ * @param[in] ptr Pointer to write buffer
+ * @param[in] len Number of bytes to write
+ *
+ * @retval Number of bytes written
  */
 int _write(int file, char *ptr, int len)
 {
-    int todo;
-
-    for (todo = 0; todo < len; todo++)
-    {
-        while(UART_FR(UART0_ADDR) & UART_FR_TXFF)
-            ;
-        UART_DR(UART0_ADDR) = *ptr++;
-    }
-
-    return len;
+    /* Write to the UART driver, regardless of file descriptor */
+    return (uart_write (ptr, len));
 }
 
 
 /**
  * \b _sbrk
  *
- * Simple stub implementation.
+ * Simple heap implementation.
  *
+ * The platform/BSP must define "end" and "heap_top" which are the heap
+ * base and top respectively.
+ *
+ * @param[in] incr Chunk size
+ *
+ * @retval Pointer to allocated chunk start
  */
 caddr_t _sbrk(int incr)
 {
@@ -191,19 +186,26 @@ caddr_t _sbrk(int incr)
  static char *heap_end = 0;
  char *prev_heap_end;
 
+    /* First time in, initialise heap base using definition from linker script */
     if (heap_end == 0)
     {
         heap_end = &end;
     }
+
+    /* Save the previous heap base */
     prev_heap_end = heap_end;
 
+    /* Check we have not passed the heap top */
     if (heap_end + incr > &heap_top)
     {
-        /* Heap and stack collision */
+        /* Heap top reached, failed to allocate */
         return (caddr_t)0;
     }
 
+    /* New heap base */
     heap_end += incr;
+
+    /* Return pointer to previous base (where our allocation starts) */
     return (caddr_t)prev_heap_end;
 }
 
diff --git a/ports/avr/uart.c b/ports/avr/uart.c
index 5d51231..763e38f 100644
--- a/ports/avr/uart.c
+++ b/ports/avr/uart.c
@@ -45,6 +45,8 @@
 #endif
 
 
+/* Local data */
+
 /*
  * Semaphore for single-threaded access to UART device
  */