diff --git a/Makefile b/Makefile
index 378f47a..35468be 100644
--- a/Makefile
+++ b/Makefile
@@ -72,21 +72,30 @@ OBJCOPY		:= $(TOOLCHAIN)-objcopy
 OBJDUMP		:= $(TOOLCHAIN)-objdump
 SIZE		:= $(TOOLCHAIN)-size
 
-# The SAM D20 series is based on an ARM Cortex M0 core
+# The SAM D20 series is based on an ARM Cortex M0+ core
 #
 #
 ARCH_FLAGS 	:= -mcpu=cortex-m0plus -mthumb
 
+# Flags to be used when semihosting
+#
+#
+ifdef SEMIHOSTING
+LDFLAGS	+= --specs=rdimon.specs -lc -lrdimon
+else
+LDFLAGS += --specs=nano.specs -lc
+endif
+
 # Compilation Flags
 #
 # Display all warnings. Compile functions and data into their own sections so
 # they can be discarded if unused.  The linker performs garbage collection of
 # unused input sections.
 #
-CFLAGS		= $(COMPILATION_FLAGS) -Wall -Wextra $(ACCEPT_WARN) -std=gnu99 \
+CFLAGS		+= $(COMPILATION_FLAGS) -Wall -Wextra $(ACCEPT_WARN) -std=gnu99 \
 			-ffunction-sections -fdata-sections $(ARCH_FLAGS)
-ASFLAGS		= -Wall $(ARCH_FLAGS) -a=/dev/null
-LDFLAGS		= $(COMPILATION_FLAGS) $(LINKER_FLAGS) -Wextra $(ARCH_FLAGS)
+ASFLAGS		+= -Wall $(ARCH_FLAGS) -a=/dev/null
+LDFLAGS		+= $(COMPILATION_FLAGS) -lm $(LINKER_FLAGS) -lm -Wextra $(ARCH_FLAGS)
 
 # Compilation Defines
 #
@@ -95,6 +104,9 @@ LDFLAGS		= $(COMPILATION_FLAGS) $(LINKER_FLAGS) -Wextra $(ARCH_FLAGS)
 ifdef TARGET_CHIP
 CFLAGS		+= -D$(TARGET_CHIP) -D__$(TARGET_CHIP)__
 endif
+ifdef SEMIHOSTING
+CFLAGS		+= -D__SEMIHOSTING__
+endif
 
 # Startup and system code
 #
@@ -226,7 +238,7 @@ etags: $(TAGFILES)
 #
 .PHONY: emacs
 emacs:
-	@emacs $(TAGFILES) Makefile config.mk
+	@emacs $(TAGFILES) Makefile config.mk README.md
 
 # Removes everything in the output directory
 #
diff --git a/README-nrf51-gcc-blackmagic.md b/README-samd20-gcc-blackmagic.md
similarity index 88%
rename from README-nrf51-gcc-blackmagic.md
rename to README-samd20-gcc-blackmagic.md
index 16ca350..04ef995 100644
--- a/README-nrf51-gcc-blackmagic.md
+++ b/README-samd20-gcc-blackmagic.md
@@ -76,6 +76,22 @@ outside of RAM and ROM.
 
 These commands can be automated by placing them in a `gdbscript-custom` file.
 
+### Semihosting ###
+
+You can build for semihosting by defining the `SEMIHOSTING` variable
+in make. Like this:
+
+```
+make -kB SEMIHOSTING=1
+```
+
+This build will be significantly larger (in terms of RAM and ROM).
+
+For this build, when a debugger is present at startup the
+`semihost_printf`, `semihost_puts` and `semihost_putchar` functions
+will print to stdio on the host. The Blackmagic Debug Probe supports
+this.
+
 ## Emacs ##
 
 The command `make emacs` can be used to quickly launch an instance of
diff --git a/README.md b/README.md
index da6714a..a8844b4 120000
--- a/README.md
+++ b/README.md
@@ -1 +1 @@
-README-nrf51-gcc-blackmagic.md
\ No newline at end of file
+README-samd20-gcc-blackmagic.md
\ No newline at end of file
diff --git a/chip/sections.ld b/chip/sections.ld
index 86943b9..fe368db 100644
--- a/chip/sections.ld
+++ b/chip/sections.ld
@@ -45,6 +45,8 @@
  *   __data_end
  *   __bss_start
  *   __bss_end
+ *   __end__
+ *   end
  *   __heap_start
  *   __heap_end
  *   __stack_end
@@ -139,6 +141,7 @@ SECTIONS
 	.heap (COPY):
 	{
 		__end__ = .;
+		end = __end__;
 		__heap_start = __end__;
 		*(.heap*)
 		__HeapLimit = .;
diff --git a/chip/startup_samd20.c b/chip/startup_samd20.c
index e9de444..7ad5242 100644
--- a/chip/startup_samd20.c
+++ b/chip/startup_samd20.c
@@ -42,6 +42,7 @@
  */
 
 #include "samd20.h"
+#include "semihosting.h"
 
 /* Initialize segments */
 extern uint32_t __fixed_start;
@@ -59,6 +60,7 @@ int main(void);
 /** \endcond */
 
 void __libc_init_array(void);
+extern void initialise_monitor_handles(void);
 
 /* Default empty handler */
 void Dummy_Handler(void);
@@ -174,6 +176,18 @@ void Reset_Handler(void)
         /* Initialize the C library */
         __libc_init_array();
 
+#ifdef __SEMIHOSTING__
+	/* If there's a debugger attached */
+	if (DSU->STATUSB.reg & DSU_STATUSB_DBGPRES) {
+
+		/* Initialise handles for semihosting */
+		initialise_monitor_handles();
+
+		/* Set semihosting functions */
+		set_semihosting();
+	}
+#endif /* __SEMIHOSTING__ */
+
         /* Branch to main function */
         main();
 
diff --git a/inc/semihosting.h b/inc/semihosting.h
new file mode 100644
index 0000000..a657841
--- /dev/null
+++ b/inc/semihosting.h
@@ -0,0 +1,56 @@
+/*
+ * Wrapper functions for semihosting
+ * Copyright (C) 2014  Richard Meadows <richardeoin>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#ifndef SEMIHOSTING_H
+#define SEMIHOSTING_H
+
+/**
+ * Please use the semihost_*() wrappers so that semihosting functions
+ * can be disables from the makefile!
+ */
+
+#ifndef __SEMIHOSTING__
+
+/* Dummy function handlers */
+#define semihost_putchar(c)
+#define semihost_puts(s)
+#define semihost_printf(...)
+
+#else
+
+/* We would get a SVC exception if we called stdio without a debug probe */
+void set_semihosting(void);
+
+/* Real function handlers */
+#define semihost_putchar(c)	__putchar(c)
+#define semihost_puts(s)	__puts(s)
+#define semihost_printf(...)	__printf(__VA_ARGS__)
+
+void __putchar(char c);
+void __puts(const char* s);
+void __printf(const char *format, ...);
+
+#endif /* __SEMIHOSTING__ */
+
+#endif /* SEMIHOSTING_H */
diff --git a/src/main.c b/src/main.c
index a4777b4..6966f58 100644
--- a/src/main.c
+++ b/src/main.c
@@ -25,6 +25,9 @@
 #include "samd20.h"
 #include "pindefs.h"
 
+#include <stdio.h>
+#include "semihosting.h"
+
 int main(void)
 {
   SystemInit();
@@ -38,6 +41,8 @@ int main(void)
   /* Configure the SysTick for 50ms interrupts */
   SysTick_Config(SystemCoreClock / 20);
 
+  semihost_printf("Hello World\n");
+
   while (1);
 }
 
diff --git a/src/semihosting.c b/src/semihosting.c
new file mode 100644
index 0000000..1871fcb
--- /dev/null
+++ b/src/semihosting.c
@@ -0,0 +1,53 @@
+/*
+ * Wrapper functions for semihosting
+ * Copyright (C) 2014  Richard Meadows <richardeoin>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include <stdio.h>
+#include <stdarg.h>
+
+#include "samd20.h"
+
+uint8_t semihosting_en = 0;
+
+void set_semihosting(void) {
+  semihosting_en = 1;
+}
+
+void __putchar(char c) {
+  if (semihosting_en) {
+    putchar(c);
+  }
+}
+void __puts(const char* s) {
+  if (semihosting_en) {
+    puts(s);
+  }
+}
+void __printf(const char *format, ...) {
+  if (semihosting_en) {
+    va_list args;
+
+    va_start(args, format);
+    vprintf(format, args);
+  }
+}