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diff --git a/examples/i2c-mcp4725-dac.cpp b/examples/i2c-mcp4725-dac.cpp
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+// i2c-mcp4725-dac.cpp
+//
+// Written by Andrew Meyer <ajm@leaflabs.com>
+// Modified by Marti Bolivar <mbolivar@leaflabs.com>
+//
+// Simple program showing how to control an MCP4725 DAC using the
+// libmaple I2C interface. There's an MCP4725 breakout board available
+// on SparkFun:
+//
+// http://www.sparkfun.com/products/8736
+//
+// How to use:
+//
+// 1. Connect the DAC SDA and SCL pins to I2C2, with a pullup
+//    resistor (1 KOhm should work) to VCC.
+// 2. Load the sketch and connect to SerialUSB.
+// 3. Press the button.
+//
+// The program then makes sure the DAC is connected properly (during
+// setup()), then has the DAC output a sawtooth wave (with loop()).
+
+#include <wirish/wirish.h>
+#include <libmaple/i2c.h>
+
+#define MCP_ADDR         0x60
+#define MCP_WRITE_DAC    0b01000000
+#define MCP_WRITE_EEPROM 0b01100000
+#define MCP_PD_NORMAL    0b00000000
+#define MCP_PD_1K        0b00000010
+#define MCP_PD_100K      0b00000100
+#define MCP_PD_500K      0b00000110
+
+static uint8 write_msg_data[3];
+static i2c_msg write_msg;
+
+static uint8 read_msg_data[5];
+static i2c_msg read_msg;
+
+/*
+ * DAC control routines
+ */
+
+void mcp_i2c_setup(void) {
+  write_msg.addr = MCP_ADDR;
+  write_msg.flags = 0; // write, 7 bit address
+  write_msg.length = sizeof(write_msg_data);
+  write_msg.xferred = 0;
+  write_msg.data = write_msg_data;
+
+  read_msg.addr = MCP_ADDR;
+  read_msg.flags = I2C_MSG_READ;
+  read_msg.length = sizeof(read_msg_data);
+  read_msg.xferred = 0;
+  read_msg.data = read_msg_data;
+}
+
+void mcp_write_val(uint16 val) {
+  write_msg_data[0] = MCP_WRITE_DAC | MCP_PD_NORMAL;
+  uint16 tmp = val >> 4;
+  write_msg_data[1] = tmp;
+  tmp = (val << 4) & 0x00FF;
+  write_msg_data[2] = tmp;
+
+  i2c_master_xfer(I2C2, &write_msg, 1, 0);
+}
+
+uint16 mcp_read_val() {
+  uint16 tmp = 0;
+
+  i2c_master_xfer(I2C2, &read_msg, 1, 2);
+
+  /* We don't care about the status and EEPROM bytes (0, 3, and 4). */
+  tmp = (read_msg_data[1] << 4);
+  tmp += (read_msg_data[2] >> 4);
+  return tmp;
+}
+
+int mcp_test() {
+  uint16 val;
+  uint16 test_val = 0x0101;
+
+  SerialUSB.println("Testing the MCP4725...");
+  /* Read the value of the register (should be 0x0800 if factory fresh) */
+  val = mcp_read_val();
+  SerialUSB.print("DAC Register = 0x");
+  SerialUSB.println(val, HEX);
+
+  mcp_write_val(test_val);
+  SerialUSB.print("Wrote 0x");
+  SerialUSB.print(test_val, HEX);
+  SerialUSB.println(" to the DAC");
+
+  val = mcp_read_val();
+  SerialUSB.print("DAC Register = 0x");
+  SerialUSB.println(val, HEX);
+
+  if (val != test_val) {
+    SerialUSB.println("ERROR: MCP4725 not responding correctly");
+    return 0;
+  }
+
+  SerialUSB.println("MCP4725 seems to be working");
+  return 1;
+}
+
+/*
+ * setup() and loop()
+ */
+
+void setup() {
+  pinMode(BOARD_BUTTON_PIN, INPUT);
+  i2c_master_enable(I2C2, 0);
+  mcp_i2c_setup();
+
+  waitForButtonPress();
+  ASSERT(mcp_test());
+
+  SerialUSB.println("Starting sawtooth wave");
+}
+
+void loop() {
+  static uint16 dout = 0;
+
+  mcp_write_val(dout);
+
+  dout += 50;
+  if (dout >= 32768) {
+    dout = 0;
+  }
+}
+
+// -- init() and main() -------------------------------------------------------
+
+__attribute__((constructor)) void premain() {
+    init();
+}
+
+int main(void) {
+    setup();
+
+    while (true) {
+        loop();
+    }
+    return 0;
+}