diff --git a/boards/samd21-xpro/include/periph_conf.h b/boards/samd21-xpro/include/periph_conf.h
index 0eec5a2a1..a346a469f 100644
--- a/boards/samd21-xpro/include/periph_conf.h
+++ b/boards/samd21-xpro/include/periph_conf.h
@@ -271,34 +271,34 @@ static const spi_conf_t spi_config[] = {
  * @name ADC Configuration
  * @{
  */
-#define ADC_NUMOF                          (1U)
 #define ADC_0_EN                           1
 #define ADC_MAX_CHANNELS                   14
 /* ADC 0 device configuration */
 #define ADC_0_DEV                          ADC
 #define ADC_0_IRQ                          ADC_IRQn
-#define ADC_0_CHANNELS                     (3U)
-/**
- * @brief ADC Channel Configuration
- */
-typedef struct {
-    gpio_t pin;            /**< ADC channel pin */
-    uint32_t muxpos;       /**< ADC channel pin multiplexer value */
-} adc_channel_t;
 
 /* ADC 0 Default values */
 #define ADC_0_CLK_SOURCE                   0 /* GCLK_GENERATOR_0 */
 #define ADC_0_PRESCALER                    ADC_CTRLB_PRESCALER_DIV512
-static const adc_channel_t adc_channels[] = {
+
+#define ADC_0_NEG_INPUT                    ADC_INPUTCTRL_MUXNEG_GND
+#define ADC_0_GAIN_FACTOR_DEFAULT          ADC_INPUTCTRL_GAIN_1X
+#define ADC_0_REF_DEFAULT                  ADC_REFCTRL_REFSEL_INT1V
+
+static const adc_conf_chan_t adc_channels[] = {
     /* port, pin, muxpos */
+    {GPIO_PIN(PB, 0), ADC_INPUTCTRL_MUXPOS_PIN8},      /* EXT1, pin 3 */
+    {GPIO_PIN(PB, 1), ADC_INPUTCTRL_MUXPOS_PIN9},      /* EXT1, pin 4 */
     {GPIO_PIN(PA, 10), ADC_INPUTCTRL_MUXPOS_PIN18},    /* EXT2, pin 3 */
     {GPIO_PIN(PA, 11), ADC_INPUTCTRL_MUXPOS_PIN19},    /* EXT2, pin 4 */
-    {GPIO_PIN(PA, 2), ADC_INPUTCTRL_MUXPOS_PIN0}       /* EXT3, pin 3 */
+    {GPIO_PIN(PA, 2), ADC_INPUTCTRL_MUXPOS_PIN0},      /* EXT3, pin 3 */
+    {GPIO_PIN(PA, 3), ADC_INPUTCTRL_MUXPOS_PIN1}       /* EXT3, pin 4. This is
+                        disconnected by default. PA3 is connected to USB_ID.
+                        Move PA03 SELECT jumper to EXT3 to connect. */
 };
 
-#define ADC_0_NEG_INPUT                    ADC_INPUTCTRL_MUXNEG_GND
-#define ADC_0_GAIN_FACTOR_DEFAULT          ADC_INPUTCTRL_GAIN_1X
-#define ADC_0_REF_DEFAULT                  ADC_REFCTRL_REFSEL_INT1V
+#define ADC_0_CHANNELS                     (6U)
+#define ADC_NUMOF                          ADC_0_CHANNELS
 /** @} */
 
 #ifdef __cplusplus
diff --git a/boards/samr21-xpro/Makefile.features b/boards/samr21-xpro/Makefile.features
index 3b09ac148..370a47e1f 100644
--- a/boards/samr21-xpro/Makefile.features
+++ b/boards/samr21-xpro/Makefile.features
@@ -1,4 +1,5 @@
 # Put defined MCU peripherals here (in alphabetical order)
+FEATURES_PROVIDED += periph_adc
 FEATURES_PROVIDED += periph_cpuid
 FEATURES_PROVIDED += periph_gpio
 FEATURES_PROVIDED += periph_i2c
diff --git a/boards/samr21-xpro/include/periph_conf.h b/boards/samr21-xpro/include/periph_conf.h
index ffde89924..f4910d0d0 100644
--- a/boards/samr21-xpro/include/periph_conf.h
+++ b/boards/samr21-xpro/include/periph_conf.h
@@ -240,6 +240,33 @@ static const spi_conf_t spi_config[] = {
 #define RTT_RUNSTDBY        (1)         /* Keep RTT running in sleep states */
 /** @} */
 
+/**
+ * @name ADC Configuration
+ * @{
+ */
+#define ADC_0_EN                           1
+#define ADC_MAX_CHANNELS                   14
+/* ADC 0 device configuration */
+#define ADC_0_DEV                          ADC
+#define ADC_0_IRQ                          ADC_IRQn
+
+/* ADC 0 Default values */
+#define ADC_0_CLK_SOURCE                   0 /* GCLK_GENERATOR_0 */
+#define ADC_0_PRESCALER                    ADC_CTRLB_PRESCALER_DIV512
+
+#define ADC_0_NEG_INPUT                    ADC_INPUTCTRL_MUXNEG_GND
+#define ADC_0_GAIN_FACTOR_DEFAULT          ADC_INPUTCTRL_GAIN_1X
+#define ADC_0_REF_DEFAULT                  ADC_REFCTRL_REFSEL_INT1V
+
+static const adc_conf_chan_t adc_channels[] = {
+    /* port, pin, muxpos */
+    {GPIO_PIN(PA, 6), ADC_INPUTCTRL_MUXPOS_PIN6},      /* EXT1, pin 3 */
+    {GPIO_PIN(PA, 7), ADC_INPUTCTRL_MUXPOS_PIN7},      /* EXT1, pin 4 */
+};
+
+#define ADC_0_CHANNELS                     (2U)
+#define ADC_NUMOF                          ADC_0_CHANNELS
+/** @} */
 #ifdef __cplusplus
 }
 #endif
diff --git a/cpu/samd21/include/periph_cpu.h b/cpu/samd21/include/periph_cpu.h
index 4be6f4597..c2ec27b98 100644
--- a/cpu/samd21/include/periph_cpu.h
+++ b/cpu/samd21/include/periph_cpu.h
@@ -99,6 +99,14 @@ typedef struct {
     uart_txpad_t tx_pad;    /**< pad selection for TX line */
 } uart_conf_t;
 
+/**
+ * @brief ADC Channel Configuration
+ */
+typedef struct {
+    gpio_t pin;            /**< ADC channel pin */
+    uint32_t muxpos;       /**< ADC channel pin multiplexer value */
+} adc_conf_chan_t;
+
 /**
  * @brief   Return the numeric id of a SERCOM device derived from its address
  *