diff --git a/docs/Todo.md b/docs/Todo.md
index a533fde9..b3dec34c 100644
--- a/docs/Todo.md
+++ b/docs/Todo.md
@@ -89,8 +89,6 @@ Documentation
 Hardware features
 =================
 
-* Support ADC on Arduino Due.
-
 * Port firmware to more architectures:
  * Beagle Bone Black PRU
  * Smoothieboard / NXP LPC1769 (ARM cortex-M3)
diff --git a/src/adccmds.c b/src/adccmds.c
index 907e05d4..49e195ac 100644
--- a/src/adccmds.c
+++ b/src/adccmds.c
@@ -18,7 +18,7 @@ struct analog_in {
     uint8_t state, sample_count;
 };
 
-static uint8_t
+static uint_fast8_t
 analog_in_event(struct timer *timer)
 {
     struct analog_in *a = container_of(timer, struct analog_in, timer);
diff --git a/src/sam3x8e/Kconfig b/src/sam3x8e/Kconfig
index 00e1f06e..179ac9b7 100644
--- a/src/sam3x8e/Kconfig
+++ b/src/sam3x8e/Kconfig
@@ -2,6 +2,11 @@
 
 if MACH_SAM3X8E
 
+config SAM_SELECT
+    bool
+    default y
+    select HAVE_GPIO_ADC
+
 config BOARD_DIRECTORY
     string
     default "sam3x8e"
diff --git a/src/sam3x8e/gpio.c b/src/sam3x8e/gpio.c
index 78fb0f05..5445c397 100644
--- a/src/sam3x8e/gpio.c
+++ b/src/sam3x8e/gpio.c
@@ -5,6 +5,7 @@
 // This file may be distributed under the terms of the GNU GPLv3 license.
 
 #include <stdint.h> // uint32_t
+#include "autoconf.h" // CONFIG_CLOCK_FREQ
 #include "command.h" // shutdown
 #include "compiler.h" // ARRAY_SIZE
 #include "gpio.h" // gpio_out_setup
@@ -113,3 +114,78 @@ gpio_in_read(struct gpio_in g)
     Pio *regs = g.regs;
     return !!(regs->PIO_PDSR & g.bit);
 }
+
+
+static const uint8_t adc_pins[] = {
+    GPIO('A', 2), GPIO('A', 3), GPIO('A', 4), GPIO('A', 6),
+    GPIO('A', 22), GPIO('A', 23), GPIO('A', 24), GPIO('A', 16),
+    GPIO('B', 12), GPIO('B', 13), GPIO('B', 17), GPIO('B', 18),
+    GPIO('B', 19), GPIO('B', 20)
+};
+
+#define ADC_FREQ_MAX 20000000
+DECL_CONSTANT(ADC_MAX, 4096);
+
+struct gpio_adc
+gpio_adc_setup(uint8_t pin)
+{
+    int chan;
+    for (chan=0; chan<ARRAY_SIZE(adc_pins); chan++) {
+        if (adc_pins[chan] != pin)
+            continue;
+        // Found PIN
+        if (!(PMC->PMC_PCER1 & (1 << (ID_ADC-32)))) {
+            // Setup ADC
+            PMC->PMC_PCER1 = 1 << (ID_ADC-32);
+            uint32_t prescal = SystemCoreClock / (2 * ADC_FREQ_MAX) - 1;
+            ADC->ADC_MR = (ADC_MR_PRESCAL(prescal)
+                           | ADC_MR_STARTUP_SUT768
+                           | ADC_MR_TRANSFER(1));
+        }
+        return (struct gpio_adc){ .bit = 1 << chan };
+    }
+    shutdown("Not a valid ADC pin");
+}
+
+// Try to sample a value. Returns zero if sample ready, otherwise
+// returns the number of clock ticks the caller should wait before
+// retrying this function.
+uint32_t
+gpio_adc_sample(struct gpio_adc g)
+{
+    uint32_t chsr = ADC->ADC_CHSR & 0xffff;
+    if (!chsr) {
+        // Start sample
+        ADC->ADC_CHER = g.bit;
+        ADC->ADC_CR = ADC_CR_START;
+        goto need_delay;
+    }
+    if (chsr != g.bit)
+        // Sampling in progress on another channel
+        goto need_delay;
+    if (!(ADC->ADC_ISR & ADC_ISR_DRDY))
+        // Conversion still in progress
+        goto need_delay;
+    // Conversion ready
+    return 0;
+need_delay:
+    return ADC_FREQ_MAX * 1000ULL / CONFIG_CLOCK_FREQ;
+}
+
+// Read a value; use only after gpio_adc_sample() returns zero
+uint16_t
+gpio_adc_read(struct gpio_adc g)
+{
+    ADC->ADC_CHDR = g.bit;
+    return ADC->ADC_LCDR;
+}
+
+// Cancel a sample that may have been started with gpio_adc_sample()
+void
+gpio_adc_cancel_sample(struct gpio_adc g)
+{
+    irqstatus_t flag = irq_save();
+    if ((ADC->ADC_CHSR & 0xffff) == g.bit)
+        gpio_adc_read(g);
+    irq_restore(flag);
+}
diff --git a/src/sam3x8e/gpio.h b/src/sam3x8e/gpio.h
index d8fdf569..0c75f642 100644
--- a/src/sam3x8e/gpio.h
+++ b/src/sam3x8e/gpio.h
@@ -20,4 +20,12 @@ struct gpio_in {
 struct gpio_in gpio_in_setup(uint8_t pin, int8_t pull_up);
 uint8_t gpio_in_read(struct gpio_in g);
 
+struct gpio_adc {
+    uint32_t bit;
+};
+struct gpio_adc gpio_adc_setup(uint8_t pin);
+uint32_t gpio_adc_sample(struct gpio_adc g);
+uint16_t gpio_adc_read(struct gpio_adc g);
+void gpio_adc_cancel_sample(struct gpio_adc g);
+
 #endif // gpio.h