diff --git a/apps/ir_spam1/Makefile b/apps/ir_spam1/Makefile
new file mode 100644
index 0000000..f751647
--- /dev/null
+++ b/apps/ir_spam1/Makefile
@@ -0,0 +1,71 @@
+# File:   Makefile
+# Author: M. P. Hayes, UCECE
+# Date:   12 Sep 2010
+# Descr:  Makefile for ir_spam1
+
+# Definitions.
+CC = avr-gcc
+CFLAGS = -mmcu=atmega32u2 -Os -Wall -Wstrict-prototypes -Wextra -g -I../../drivers/avr -I../../utils
+OBJCOPY = avr-objcopy
+SIZE = avr-size
+DEL = rm
+
+
+# Default target.
+all: ir_spam1.out
+
+
+# Compile: create object files from C source files.
+ir_spam1.o: ir_spam1.c ../../drivers/avr/ir_uart.h ../../drivers/avr/system.h ../../utils/pacer.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+ir_uart.o: ../../drivers/avr/ir_uart.c ../../drivers/avr/ir_uart.h ../../drivers/avr/pio.h ../../drivers/avr/system.h ../../drivers/avr/timer0.h ../../drivers/avr/usart1.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+pio.o: ../../drivers/avr/pio.c ../../drivers/avr/pio.h ../../drivers/avr/system.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+prescale.o: ../../drivers/avr/prescale.c ../../drivers/avr/prescale.h ../../drivers/avr/system.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+system.o: ../../drivers/avr/system.c ../../drivers/avr/system.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+timer.o: ../../drivers/avr/timer.c ../../drivers/avr/system.h ../../drivers/avr/timer.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+timer0.o: ../../drivers/avr/timer0.c ../../drivers/avr/bits.h ../../drivers/avr/prescale.h ../../drivers/avr/system.h ../../drivers/avr/timer0.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+usart1.o: ../../drivers/avr/usart1.c ../../drivers/avr/system.h ../../drivers/avr/usart1.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+pacer.o: ../../utils/pacer.c ../../drivers/avr/system.h ../../drivers/avr/timer.h ../../utils/pacer.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+
+
+
+# Link: create output file (executable) from object files.
+ir_spam1.out: ir_spam1.o ir_uart.o pio.o prescale.o system.o timer.o timer0.o usart1.o pacer.o
+	$(CC) $(CFLAGS) $^ -o $@ -lm
+	$(SIZE) $@
+
+
+# Create hex file for programming from executable file.
+ir_spam1.hex: ir_spam1.out
+	$(OBJCOPY) -O ihex ir_spam1.out ir_spam1.hex
+
+
+# Target: clean project.
+.PHONY: clean
+clean: 
+	-$(DEL) *.o *.out *.hex
+
+
+# Target: program project.
+.PHONY: program
+program: ir_spam1.hex
+	dfu-programmer atmega32u2 erase; dfu-programmer atmega32u2 flash ir_spam1.hex; dfu-programmer atmega32u2 start
+
+
diff --git a/apps/ir_spam1/Makefile.test b/apps/ir_spam1/Makefile.test
new file mode 100644
index 0000000..772517a
--- /dev/null
+++ b/apps/ir_spam1/Makefile.test
@@ -0,0 +1,52 @@
+# File:   Makefile
+# Author: M. P. Hayes, UCECE
+# Date:   11 Sep 2010
+# Descr:  Makefile for ir_spam1
+
+CC = gcc
+CFLAGS = -Wall -Wstrict-prototypes -Wextra -g -I../../drivers/test -I../../utils
+
+DEL = rm
+
+
+# Default target.
+all: ir_spam1
+
+
+# Compile: create object files from C source files.
+ir_spam1-test.o: ir_spam1.c ../../drivers/test/ir_uart.h ../../drivers/test/system.h ../../utils/pacer.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+ir_uart-test.o: ../../drivers/test/ir_uart.c ../../drivers/test/ir_uart.h ../../drivers/test/system.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+mgetkey-test.o: ../../drivers/test/mgetkey.c ../../drivers/test/mgetkey.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+pio-test.o: ../../drivers/test/pio.c ../../drivers/test/avrtest.h ../../drivers/test/pio.h ../../drivers/test/system.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+system-test.o: ../../drivers/test/system.c ../../drivers/test/avrtest.h ../../drivers/test/mgetkey.h ../../drivers/test/pio.h ../../drivers/test/system.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+timer-test.o: ../../drivers/test/timer.c ../../drivers/test/system.h ../../drivers/test/timer.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+pacer-test.o: ../../utils/pacer.c ../../drivers/test/system.h ../../drivers/test/timer.h ../../utils/pacer.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+
+
+
+# Link: create executable file from object files.
+ir_spam1: ir_spam1-test.o ir_uart-test.o mgetkey-test.o pio-test.o system-test.o timer-test.o pacer-test.o
+	$(CC) $(CFLAGS) $^ -o $@ -lrt
+
+
+# Clean: delete derived files.
+.PHONY: clean
+clean: 
+	-$(DEL) ir_spam1 ir_spam1-test.o ir_uart-test.o mgetkey-test.o pio-test.o system-test.o timer-test.o pacer-test.o
+
+
+
diff --git a/apps/ir_spam1/doc/Makefile b/apps/ir_spam1/doc/Makefile
new file mode 100644
index 0000000..00afecd
--- /dev/null
+++ b/apps/ir_spam1/doc/Makefile
@@ -0,0 +1,45 @@
+# File:   Makefile
+# Author: M. P. Hayes, UCECE
+# Date:   11 Sep 2010
+# Descr:  Makefile for ir_uart_test1 docs
+
+# The scripts used to make the graphs require the program dot; this
+# is part of the graphviz package.
+
+DEL = rm
+
+all: file_dependencies.pdf module_dependencies.pdf makefile_dependencies.pdf build_dependencies.pdf callgraph.pdf
+
+file_dependencies.pdf: files.d 
+	../../../etc/graphdeps.py $< --out $@
+
+module_dependencies.pdf: modules.d 
+	../../../etc/graphdeps.py $< --modules --rotate --out $@
+
+makefile_dependencies.pdf: ../Makefile
+	../../../etc/graphdeps.py $< --out $@
+
+build_dependencies.pdf: ../Makefile
+	../../../etc/graphdeps.py $< --out $@ --showops
+
+callgraph.pdf: callgraph.d
+	../../../etc/graphdeps.py --calls --modules $< --out $@ --showops
+
+
+files.d: ../Makefile
+	(cd ..;	../../etc/makemake.py --relpath --files . . ../../drivers ../../drivers/avr ../../utils ../../extra --exclude system.h > doc/files.d)
+
+
+modules.d: ../Makefile
+	(cd ..;	../../etc/makemake.py --relpath --modules . . ../../drivers ../../drivers/avr ../../utils ../../extra --exclude system > doc/modules.d)
+
+
+callgraph.d: ../Makefile
+	(cd ..;	../../etc/makemake.py --cc="avr-gcc" --cflags="-Os -mmcu=atmega32u2" --relpath --calls . . ../../drivers ../../drivers/avr ../../utils ../../extra --exclude system.h > doc/callgraph.d)
+
+
+# Clean: delete derived files.
+.PHONY: clean
+clean: 
+	-$(DEL) *.d *.pdf
+
diff --git a/apps/ir_spam1/doc/README b/apps/ir_spam1/doc/README
new file mode 100644
index 0000000..39a9712
--- /dev/null
+++ b/apps/ir_spam1/doc/README
@@ -0,0 +1,16 @@
+Running make in this directory will generate a number of PDF graphs.
+In the callgraph, the arrows means "calls".  In the dependency graphs,
+the arrows means "requires" (or "depends upon").
+
+callgraph.pdf             This shows the callgraph, i.e., what functions each
+                          function in the program calls.
+module_dependencies.pdf   This shows the dependencies between the modules.
+file_dependencies.pdf     This shows the dependencies between the files.
+makefile_dependencies.pdf This shows the dependencies required by make when
+                          building the program.
+build_dependencies.pdf    This is like makefile_dependencies.pdf but shows
+                          the operations performed to generate the new file.
+
+callgraph.d               This shows the callgraph in text format.
+files.d                   This shows the file dependencies in text format.
+modules.d                 This shows the module dependencies in text format.
diff --git a/apps/ir_spam1/ir_spam1.c b/apps/ir_spam1/ir_spam1.c
new file mode 100644
index 0000000..f61f497
--- /dev/null
+++ b/apps/ir_spam1/ir_spam1.c
@@ -0,0 +1,35 @@
+/** @file   ir_spam1.c
+    @author M. P. Hayes, UCECE
+    @date   24 September 2013
+    @brief  Repeatedly send message over IR.
+*/
+
+#include "system.h"
+#include "pacer.h"
+#include "ir_uart.h"
+
+/* Define polling rate in Hz.  */
+#define LOOP_RATE 20
+
+
+int main (void)
+{
+    int count = 5;
+
+    system_init ();
+
+    ir_uart_init ();
+
+    pacer_init (LOOP_RATE);
+
+    /* Paced loop.  */
+    while (1)
+    {
+        /* Wait for next tick.  */
+        pacer_wait ();
+        
+        ir_uart_putc ('A');
+    }
+
+    return 0;
+}
diff --git a/apps/pacerdemo1/Makefile.test b/apps/pacerdemo1/Makefile.test
new file mode 100644
index 0000000..0e6e90b
--- /dev/null
+++ b/apps/pacerdemo1/Makefile.test
@@ -0,0 +1,52 @@
+# File:   Makefile
+# Author: M. P. Hayes, UCECE
+# Date:   11 Sep 2010
+# Descr:  Makefile for pacerdemo1
+
+CC = gcc
+CFLAGS = -Wall -Wstrict-prototypes -Wextra -g -I../../drivers/test -I../../drivers -I../../utils
+
+DEL = rm
+
+
+# Default target.
+all: pacerdemo1
+
+
+# Compile: create object files from C source files.
+pacerdemo1-test.o: pacerdemo1.c ../../drivers/led.h ../../drivers/test/avrtest.h ../../drivers/test/pio.h ../../drivers/test/system.h ../../utils/pacer.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+led-test.o: ../../drivers/led.c ../../drivers/led.h ../../drivers/test/avrtest.h ../../drivers/test/pio.h ../../drivers/test/system.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+mgetkey-test.o: ../../drivers/test/mgetkey.c ../../drivers/test/mgetkey.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+pio-test.o: ../../drivers/test/pio.c ../../drivers/test/avrtest.h ../../drivers/test/pio.h ../../drivers/test/system.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+system-test.o: ../../drivers/test/system.c ../../drivers/test/avrtest.h ../../drivers/test/mgetkey.h ../../drivers/test/pio.h ../../drivers/test/system.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+timer-test.o: ../../drivers/test/timer.c ../../drivers/test/system.h ../../drivers/test/timer.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+pacer-test.o: ../../utils/pacer.c ../../drivers/test/system.h ../../drivers/test/timer.h ../../utils/pacer.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+
+
+
+# Link: create executable file from object files.
+pacerdemo1: pacerdemo1-test.o led-test.o mgetkey-test.o pio-test.o system-test.o timer-test.o pacer-test.o
+	$(CC) $(CFLAGS) $^ -o $@ -lrt
+
+
+# Clean: delete derived files.
+.PHONY: clean
+clean: 
+	-$(DEL) pacerdemo1 pacerdemo1-test.o led-test.o mgetkey-test.o pio-test.o system-test.o timer-test.o pacer-test.o
+
+
+
diff --git a/drivers/avr/system.c b/drivers/avr/system.c
index f7b30af..f494d96 100644
--- a/drivers/avr/system.c
+++ b/drivers/avr/system.c
@@ -30,6 +30,7 @@ static void system_watchdog_timer_init (void)
 }
 
 
+/** Initialise clock and disable watchdog timer.  */
 void system_init (void)
 {
     system_clock_init ();
diff --git a/drivers/avr/system.h b/drivers/avr/system.h
index f2e2e92..670542e 100644
--- a/drivers/avr/system.h
+++ b/drivers/avr/system.h
@@ -12,7 +12,7 @@
 typedef uint8_t bool;
 
 
-/* Useful macros.  */
+/** Useful macros.  */
 #define BIT(X) (1 << (X))
 
 #define ARRAY_SIZE(ARRAY) (sizeof (ARRAY) / sizeof (ARRAY[0]))
@@ -20,11 +20,11 @@ typedef uint8_t bool;
 #define  __unused__ __attribute__ ((unused))
 
 
-/* Clock frequency Hz.  */
+/** Clock frequency Hz.  */
 #define F_CPU 8000000
 
 
-/* LED matrix columns.  (Note these are labelled in reverse order on
+/** LED matrix columns.  (Note these are labelled in reverse order on
    the schematic.)  */
 #define LEDMAT_COL1_PIO PC6_PIO
 #define LEDMAT_COL2_PIO PB7_PIO
@@ -34,7 +34,7 @@ typedef uint8_t bool;
 #define LEDMAT_COLS_NUM 5
 
 
-/* LED matrix rows.  */
+/** LED matrix rows.  */
 #define LEDMAT_ROW1_PIO PB6_PIO
 #define LEDMAT_ROW2_PIO PB5_PIO
 #define LEDMAT_ROW3_PIO PB4_PIO 
@@ -45,12 +45,12 @@ typedef uint8_t bool;
 #define LEDMAT_ROWS_NUM 7
 
 
-/* Button.  */
+/** Button.  */
 #define BUTTON1 0
 #define BUTTON1_PIO PD7_PIO
 
 
-/* Navswitch.  */
+/** Navswitch.  */
 #define NAVSWITCH_PUSH_PIO LEDMAT_COL3_PIO
 #define NAVSWITCH_DOWN_PIO NAVSWITCH_PUSH_PIO 
 #define NAVSWITCH_EAST_PIO LEDMAT_COL1_PIO
@@ -59,18 +59,19 @@ typedef uint8_t bool;
 #define NAVSWITCH_SOUTH_PIO LEDMAT_COL5_PIO
 
 
-/* LED (active high).  */
+/** LED (active high).  */
 #define LED1 0
 #define LED1_PIO PC2_PIO
 
 
-/* Infrared transmitter LED and receiver.  */
+/** Infrared transmitter LED and receiver.  */
 #define IR_TX_LOW_PIO PD3_PIO 
 #define IR_TX_HIGH_PIO PD0_PIO
 #define IR_RX_PIO PD2_PIO
 
 #define IR_MODULATION_FREQ 36e3
 
+/** Initialise clock and disable watchdog timer.  */
 void system_init (void);
 
 #endif
diff --git a/drivers/ir_rx5_rx.c b/drivers/ir_rx5_rx.c
new file mode 100644
index 0000000..0d8fab3
--- /dev/null
+++ b/drivers/ir_rx5_rx.c
@@ -0,0 +1,151 @@
+/** @file   ir_rc5_rx.c
+    @author M. P. Hayes, UCECE
+    @date   21 May 2013
+    @brief  Infrared serial receiver driver for Phillips RC5 protocol.
+*/
+
+/* The Phillips RC-5 protocol uses the following format of 14 bits:
+   1 start bit
+   1 field bit (this used to be a second start bit)
+   1 toggle bit
+   5 address bits
+   6 command bits
+ 
+   Manchester encoding is used for the bits.  The start bit is a `1' bits.
+   `1' bits have the IR modulation on for the second half of the cycle.
+   `0' bits have the IR modulation on for the first half of the cycle.
+
+   Each bit period is 1778 microseconds (64 cycles of 36 kHz modulation)
+   thus a frame is 24.9 ms.
+
+   While a button is pressed, a frame is repeatedly sent.  If the button
+   is repressed, the toggle bit is changed.
+
+   This is a simple polled implementation that will block for the entire frame
+   if it detects a start bit.
+*/
+
+
+#include "ir_rc5_rx.h"
+#include "pio.h"
+#include "delay.h"
+
+#define IR_RC5_BIT_PERIOD_US 1778
+
+#ifndef IR_RC5_RX_ACTIVE_STATE
+/* Most IR demodulators have an active low output.  */
+#define IR_RC5_RX_ACTIVE_STATE 0
+#endif
+
+
+/** Return output state of IR receiver.
+    @return IR receiver state (1 = IR modulation detected).  */
+static inline uint8_t ir_rc5_rx_get (void)
+{
+    return pio_input_get (IR_RC5_RX_PIO) == IR_RC5_RX_ACTIVE_STATE;
+}
+
+
+uint8_t ir_rc5_rx_ready_p (void)
+{
+    return ir_rc5_rx_get ();
+}
+
+
+static uint16_t ir_rc5_rx_wait_state (uint8_t state)
+{
+    uint16_t us;
+    
+    for (us = 0; us < IR_RC5_BIT_PERIOD_US; us++)
+    {
+        if (ir_rc5_rx_get () == state)
+            return us;
+        /* TODO: figure out how to determine the fudge term.  Ideally,
+           we should poll a counter incremented by the CPU clock.  */
+        DELAY_US (1 - 0.4);
+    }
+    return us;
+}
+
+
+static uint16_t ir_rc5_rx_wait_transition (void)
+{
+    uint8_t initial;
+    
+    initial = ir_rc5_rx_get ();
+
+    return ir_rc5_rx_wait_state (!initial);
+}
+
+
+/** Receive RC5 data packet over IR serial link.  
+    @return 14-bits of data or error status code
+    @note No error checking is performed.  If there is no activity on the
+    IR serial link, this function returns immediately.  Otherwise, this
+    function blocks until the entire frame is received.  This must be called
+    frequently to ensure that a start bit is seen.  */
+int16_t ir_rc5_rx_read (void)
+{
+    int16_t data;
+    int i;
+    uint16_t us;
+
+    /* Look to see if there is some IR modulation marking the second
+       half of the first start bit.  It is possible that we may have
+       missed the start bit.  In this case we are likely to
+       time out.  */
+    if (!ir_rc5_rx_ready_p ())
+        return IR_RC5_RX_NONE;
+
+    /* The old RC-5 format had two start bits; this made a bit-bashed
+       software implementation easier.  The problem is that we have
+       been called just before the falling edge of the start bit.
+       So we have to special case these two bits.  */
+
+    /* Search for the next falling transition.  */
+    us = ir_rc5_rx_wait_state (0);
+    if (us >= IR_RC5_BIT_PERIOD_US)
+        return IR_RC5_RX_TIMEOUT;
+
+    if (us > (IR_RC5_BIT_PERIOD_US >> 1))
+    {
+        /* The field bit is 0.  */
+        data = 2;
+    }
+    else
+    {
+        /* The field bit is 1; so delay until middle of bit period.  */
+        data = 3;
+        us = ir_rc5_rx_wait_state (1);
+        if (us >= IR_RC5_BIT_PERIOD_US)
+            return IR_RC5_RX_TIMEOUT;
+    }
+
+    for (i = 2; i < 14; i++)
+    {
+        data <<= 1;
+        
+        DELAY_US (0.5 * IR_RC5_BIT_PERIOD_US + 100);
+
+        us = ir_rc5_rx_wait_transition ();
+        if (us >= IR_RC5_BIT_PERIOD_US)
+            return IR_RC5_RX_TIMEOUT;
+
+        if (ir_rc5_rx_get ())
+            data |= 1;
+    }
+
+    return data;
+}
+
+
+/** Initialise IR serial receiver driver.  */
+void ir_rc5_rx_init (void)
+{
+    /* Ensure PIO clock activated for reading.  */
+    pio_init (IR_RX_PIO);
+
+    /* Configure IR receiver PIO as input.  */
+    pio_config_set (IR_RX_PIO, PIO_INPUT);
+}
+
diff --git a/drivers/ir_rx5_rx.h b/drivers/ir_rx5_rx.h
new file mode 100644
index 0000000..803aa6d
--- /dev/null
+++ b/drivers/ir_rx5_rx.h
@@ -0,0 +1,34 @@
+/** @file   ir_rc5_rx.h
+    @author M. P. Hayes, UCECE
+    @date   21 May 2013
+    @brief  Infrared serial receiver driver for Phillips RC5 protocol.
+*/
+
+#ifndef IR_RC5_RX_H
+#define IR_RC5_RX_H
+
+#include "config.h"
+
+/** Status return codes.  */
+typedef enum ir_rc5_rx_ret 
+{
+    /** No data to read.  */
+    IR_RC5_RX_NONE = 0,
+    /** Timeout waiting for transition.  */
+    IR_RC5_RX_TIMEOUT = -1
+} ir_rc5_rx_ret_t;
+
+
+/** Receive RC5 data packet over IR serial link.  
+    @return 14-bits of data or error status code
+    @note No error checking is performed.  If there is no activity on the
+    IR serial link, this function returns immediately.  Otherwise, this
+    function blocks until the entire frame is received.  This must be called
+    frequently to ensure that a start bit is seen.  */
+int16_t ir_rc5_rx_read (void);
+
+
+/** Initialise IR serial receiver driver.  */
+void ir_rc5_rx_init (void);
+
+#endif