diff --git a/Makefile b/Makefile
index 1c403a2..60da885 100644
--- a/Makefile
+++ b/Makefile
@@ -2,15 +2,16 @@
 
 NAME=quad
 
-OBJS=crt0.o main.o
+SSRCS=crt0.s
+CSRCS=main.c i2c.c
 
-CFLAGS=-march=armv4t -msoft-float
+CFLAGS=-march=armv4t -msoft-float -O1
 
 LDSCRIPT=lpc2103_flash.ld
 CC=arm-elf-gcc
 OBJCOPY=arm-elf-objcopy
 
-CLEANOBJS=$(OBJS) $(NAME).hex $(NAME).elf $(NAME).bin $(NAME).map
+CLEANOBJS=$(OBJS) $(NAME).hex $(NAME).elf $(NAME).bin $(NAME).map .depend
 
 all: $(NAME).bin
 
@@ -18,6 +19,9 @@ all: $(NAME).bin
 # In theory, nothing below here needs touching for as long as all of the
 # sources are in a single directory.
 
+COBJS=$(CSRCS:.c=.o)
+SOBJS=$(SSRCS:.s=.o)
+OBJS=$(SOBJS) $(COBJS)
 
 .SUFFIXES: .elf .hex .bin
 
@@ -36,3 +40,7 @@ run: $(NAME).hex
 clean:
 	rm -rf $(CLEANOBJS)
 
+depend:
+	$(CC) -MM $(CFLAGS) -nostdlib -nostartfiles $(CSRCS) >.depend
+
+.sinclude ".depend"
diff --git a/i2c.c b/i2c.c
new file mode 100644
index 0000000..9620d2d
--- /dev/null
+++ b/i2c.c
@@ -0,0 +1,104 @@
+
+#include "i2c.h"
+
+#define I2CBASE  0xE001C000
+
+#define I2CONSET 0x00
+#define I2STAT   0x04
+#define I2DAT    0x08
+#define I2ADR    0x0c
+#define I2SCLH   0x10
+#define I2SCLL   0x14
+#define I2CONCLR 0x18
+
+#define IREG(x) (((volatile unsigned char *)I2CBASE)[x])
+#define IWREG(x) (((volatile unsigned int *)I2CBASE)[(x)/sizeof(unsigned int)])
+
+#define AAFLAG (1<<2)
+#define SIFLAG (1<<3)
+#define STOFLAG (1<<4)
+#define STAFLAG (1<<5)
+
+#define SI (IREG(I2CONSET) & SIFLAG)
+
+void init_i2c(void)
+{
+	IREG(I2CONSET) = 0x40; /* Enable I2C ready for Master Tx */
+	/* Set up for just under 400kHz */
+#if 0
+	IWREG(I2SCLL) = (25 * 100);
+	IWREG(I2SCLH) = (12 * 100);
+#else
+	IWREG(I2SCLL) = 1475; /* ~5kHz */
+	IWREG(I2SCLH) = 1475;
+#endif
+}
+
+int i2cstat;
+
+int i2c_wait(void)
+{
+	int stat;
+	while (!SI);
+	stat = IREG(I2STAT);
+	i2cstat = stat;
+	return stat;
+}
+
+void i2c_go(void)
+{
+	IREG(I2CONCLR) = SIFLAG;
+}
+
+int i2c_conreg(void)
+{
+	return IREG(I2CONSET);
+}
+
+int i2c_statreg(void)
+{
+	return IREG(I2STAT);
+}
+
+bool i2c_send_start(void)
+{
+	IREG(I2CONCLR) = STOFLAG | STAFLAG;
+	IREG(I2CONSET) = STAFLAG;
+/*	i2c_go(); */
+	switch (i2c_wait()) {
+	case 0x08:
+	case 0x10:
+/*		IREG(I2CONCLR) = STAFLAG; */
+		return TRUE;
+	default:
+/*		IREG(I2CONCLR) = STAFLAG; */
+		return FALSE;
+	}
+}
+
+bool i2c_send_address(int addr, bool write)
+{
+	return i2c_send_data((addr<<1) + (write?0:1));
+}
+
+bool i2c_send_data(int data)
+{
+	IREG(I2DAT) = data;
+	IREG(I2CONCLR) = STAFLAG | SIFLAG;
+	switch (i2c_wait()) {
+	case 0x18:
+	case 0x28:
+		return TRUE;
+	default:
+		return FALSE;
+	}
+}
+
+void i2c_send_stop(void)
+{
+	IREG(I2CONCLR) = STAFLAG | AAFLAG;
+	IREG(I2CONSET) = STOFLAG;
+	i2c_go();
+	/* Don't think we need to wait here. Could be wrong. */
+}
+
diff --git a/i2c.h b/i2c.h
new file mode 100644
index 0000000..45a7bc4
--- /dev/null
+++ b/i2c.h
@@ -0,0 +1,11 @@
+#include "types.h"
+void init_i2c(void);
+extern int i2cstat;
+int i2c_wait(void);
+void i2c_go(void);
+int i2c_conreg(void);
+int i2c_statreg(void);
+bool i2c_send_start(void);
+bool i2c_send_address(int addr, bool write);
+bool i2c_send_data(int data);
+void i2c_send_stop(void);
diff --git a/main.c b/main.c
index 497aa39..3384eb4 100644
--- a/main.c
+++ b/main.c
@@ -1,4 +1,6 @@
 
+#include "i2c.h"
+
 #define UARTBASE 0xE000C000
 
 #define RBR 0x00
@@ -16,29 +18,47 @@
 #define FDR 0x28
 #define TER 0x30
 
-#define REG(x) (((volatile unsigned char *)UARTBASE)[x])
+#define UREG(x) (((volatile unsigned char *)UARTBASE)[x])
+
+#define U0THRE ((UREG(LSR) & (1<<5))) /* UART0 transmitter holding register is empty */
+#define U0DR ((UREG(LSR) & (1<<0))) /* UART0 data ready */
+
+
+#define I2CBASE  0xE001C000
+
+#define I2CONSET 0x00
+#define I2STAT   0x04
+#define I2DAT    0x08
+#define I2ADR    0x0c
+#define I2SCLH   0x10
+#define I2SCLL   0x14
+#define I2CONCLR 0x18
+
+#define IREG(x) (((volatile unsigned char *)I2CBASE)[x])
 
-#define U0THRE ((REG(LSR) & (1<<5))) /* UART0 transmitter holding register is empty */
-#define U0DR ((REG(LSR) & (1<<0))) /* UART0 data ready */
 
 #define PINSEL0 (*((volatile unsigned char *) 0xE002C000))
 
 void init_uart(void)
 {
-	REG(FDR) = 0x10; /* DivAddVal = 0, MulVal = 1 */
+	UREG(FDR) = 0x10; /* DivAddVal = 0, MulVal = 1 */
 
-	REG(LCR) = 0x80;
-	REG(DLM) = 0x00;
-	REG(DLL) = 0x08; /* 14745600 / (16*115200) */
-	REG(LCR) = 0x13;
-	REG(FCR) = 0x07;
+	UREG(LCR) = 0x80;
+	UREG(DLM) = 0x00;
+	UREG(DLL) = 0x08; /* 14745600 / (16*115200) */
+	UREG(LCR) = 0x13;
+	UREG(FCR) = 0x07;
+}
 
-	PINSEL0 = 0x00000005; /* P0.0 and P0.1 assigned to UART */
+void init_pins(void)
+{
+	PINSEL0 = 0x00000055; /* P0.0 and P0.1 assigned to UART */
+			      /* P0.2 and P0.3 assigned to I2C  */
 }
 
 void putch(char c) {
 	while (!U0THRE);
-	REG(THR) = c;
+	UREG(THR) = c;
 }
 
 void putstr(char *s) {
@@ -59,9 +79,26 @@ void putint(unsigned int n) {
 	putstr(s+i);
 }
 
+void puthex(unsigned int n) {
+	char s[9];
+	int i;
+
+	i = 8;
+	s[i] = '\0';
+
+	do {
+		int x = n % 16;
+		if (x > 9)
+			x += 'A' - '0' - 10;
+		s[--i] = x + '0';
+	} while ((n /= 16) > 0);
+
+	putstr(s+i);
+}
+
 char getch(void) {
 	while (!U0DR);
-	return REG(RBR);
+	return UREG(RBR);
 }
 
 void reply(char *str)
@@ -74,6 +111,8 @@ unsigned int count = 0;
 
 int main(void) {
 	init_uart();
+	init_i2c();
+	init_pins();
 	putstr("Your entire life has been a mathematical error... a mathematical error I'm about to correct!\r\n");
 
 	while (1) {
@@ -101,6 +140,49 @@ int main(void) {
 		case '?':
 			reply("Help is not available. Try a psychiatrist.");
 			break;
+		case 'R':
+			putstr("I2C register is: ");
+			puthex(i2c_conreg());
+			reply(".");
+			break;
+		case 'T':
+			putstr("I2C status was: ");
+			puthex(i2cstat);
+			putstr(" I2C status is: ");
+			puthex(i2c_statreg());
+			reply(".");
+			break;
+		case 'S':
+			putstr("Sending START... ");
+			if (i2c_send_start())
+				reply("OK");
+			else
+				reply("FAIL");
+			break;
+		case 'D':
+			putstr("Sending address... ");
+			if (i2c_send_address(0x53, TRUE))
+				reply("OK");
+			else
+				reply("FAIL");
+			break;
+		case 'B':
+			putstr("Sending bytes... ");
+			if (i2c_send_data(0xfe))
+				reply("OK");
+			else
+				reply("FAIL");
+
+			if (i2c_send_data(0x04))
+				reply("OK");
+			else
+				reply("FAIL");
+			break;
+		case 'O':
+			putstr("Sending STOP... ");
+			i2c_send_stop();
+			reply("sent");
+			break;
 		default:
 			reply("Unrecognised command.");
 			break;
diff --git a/types.h b/types.h
new file mode 100644
index 0000000..680c9a6
--- /dev/null
+++ b/types.h
@@ -0,0 +1,3 @@
+typedef int bool;
+#define TRUE 1
+#define FALSE 0