diff --git a/atmel-samd/common-hal/analogio/AnalogIn.c b/atmel-samd/common-hal/analogio/AnalogIn.c
index c520b407d02a2..03c502dff7baa 100644
--- a/atmel-samd/common-hal/analogio/AnalogIn.c
+++ b/atmel-samd/common-hal/analogio/AnalogIn.c
@@ -38,13 +38,6 @@
 #include "asf/sam0/drivers/adc/adc.h"
 #include "samd21_pins.h"
 
-// Number of active ADC channels.
-volatile uint8_t active_channel_count;
-
-// Shared between all the instances. Allocated only when needed.
-struct adc_module *adc_instance = NULL;
-struct adc_config *config_adc = NULL;
-
 void common_hal_analogio_analogin_construct(analogio_analogin_obj_t* self,
         const mcu_pin_obj_t *pin) {
     if (!pin->has_adc) {
@@ -54,27 +47,6 @@ void common_hal_analogio_analogin_construct(analogio_analogin_obj_t* self,
     claim_pin(pin);
 
     self->pin = pin;
-
-    if (adc_instance == NULL) {
-        // Allocate strucs on the heap so we only use the memory when we
-        // need it.
-        adc_instance = gc_alloc(sizeof(struct adc_module), false);
-        config_adc = gc_alloc(sizeof(struct adc_config), false);
-
-        adc_get_config_defaults(config_adc);
-
-        config_adc->reference = ADC_REFERENCE_INTVCC1;
-        config_adc->gain_factor = ADC_GAIN_FACTOR_DIV2;
-        config_adc->positive_input = self->pin->adc_input;
-        config_adc->resolution = ADC_RESOLUTION_16BIT;
-        config_adc->clock_prescaler = ADC_CLOCK_PRESCALER_DIV128;
-
-        adc_init(adc_instance, ADC, config_adc);
-    }
-
-    self->adc_instance = adc_instance;
-    self->config_adc = config_adc;
-    active_channel_count++;
 }
 
 bool common_hal_analogio_analogin_deinited(analogio_analogin_obj_t *self) {
@@ -85,36 +57,30 @@ void common_hal_analogio_analogin_deinit(analogio_analogin_obj_t *self) {
     if (common_hal_analogio_analogin_deinited(self)) {
         return;
     }
-    active_channel_count--;
-    if (active_channel_count == 0) {
-        adc_reset(adc_instance);
-        gc_free(adc_instance);
-        gc_free(config_adc);
-        // Set our references to NULL so the GC doesn't mistakenly see the
-        // pointers in memory.
-        adc_instance = NULL;
-        config_adc = NULL;
-    }
     reset_pin(self->pin->pin);
     self->pin = mp_const_none;
 }
 
 void analogin_reset() {
-    if (adc_instance != NULL) {
-        adc_reset(adc_instance);
-        adc_instance = NULL;
-    }
-    active_channel_count = 0;
 }
 
 uint16_t common_hal_analogio_analogin_get_value(analogio_analogin_obj_t *self) {
     // Something else might have used the ADC in a different way,
-    // so we have to completely re-initialize it.
-    // ADC must have been disabled before adc_init() is called.
-    adc_init(adc_instance, ADC, config_adc);
-    config_adc->positive_input = self->pin->adc_input;
+    // so we completely re-initialize it.
 
-    adc_enable(adc_instance);
+    struct adc_config config_adc;
+    adc_get_config_defaults(&config_adc);
+
+    config_adc.reference = ADC_REFERENCE_INTVCC1;
+    config_adc.gain_factor = ADC_GAIN_FACTOR_DIV2;
+    config_adc.positive_input = self->pin->adc_input;
+    config_adc.resolution = ADC_RESOLUTION_16BIT;
+    config_adc.clock_prescaler = ADC_CLOCK_PRESCALER_DIV128;
+
+    struct adc_module adc_instance;
+    // ADC must have been disabled before adc_init() is called.
+    adc_init(&adc_instance, ADC, &config_adc);
+    adc_enable(&adc_instance);
 
     // Read twice and discard first result, as recommended in section 14 of
     // http://www.atmel.com/images/Atmel-42645-ADC-Configurations-with-Examples_ApplicationNote_AT11481.pdf
@@ -125,23 +91,23 @@ uint16_t common_hal_analogio_analogin_get_value(analogio_analogin_obj_t *self) {
     uint16_t data;
     enum status_code status;
 
-    adc_start_conversion(adc_instance);
+    adc_start_conversion(&adc_instance);
     do {
-      status = adc_read(adc_instance, &data);
+      status = adc_read(&adc_instance, &data);
     }  while (status == STATUS_BUSY); 
     if (status == STATUS_ERR_OVERFLOW) {
-      // TODO(tannewt): Throw an error.
+        mp_raise_RuntimeError("ADC result overwritten before reading");
     }
 
-    adc_start_conversion(adc_instance);
+    adc_start_conversion(&adc_instance);
     do {
-        status = adc_read(adc_instance, &data);
+        status = adc_read(&adc_instance, &data);
     } while (status == STATUS_BUSY);
     if (status == STATUS_ERR_OVERFLOW) {
-      // TODO(tannewt): Throw an error.
+        mp_raise_RuntimeError("ADC result overwritten before reading");
     }
 
-    adc_disable(adc_instance);
+    adc_disable(&adc_instance);
     return data;
 }
 
diff --git a/atmel-samd/common-hal/analogio/AnalogIn.h b/atmel-samd/common-hal/analogio/AnalogIn.h
index 3e9ddd76e47c6..a4d5b355dae39 100644
--- a/atmel-samd/common-hal/analogio/AnalogIn.h
+++ b/atmel-samd/common-hal/analogio/AnalogIn.h
@@ -41,8 +41,6 @@
 typedef struct {
     mp_obj_base_t base;
     const mcu_pin_obj_t * pin;
-    struct adc_module * adc_instance;
-    struct adc_config * config_adc;
 } analogio_analogin_obj_t;
 
 void analogin_reset(void);
diff --git a/atmel-samd/main.c b/atmel-samd/main.c
index 36d5dde27377b..fe56410c055f3 100644
--- a/atmel-samd/main.c
+++ b/atmel-samd/main.c
@@ -203,6 +203,7 @@ void reset_samd21(void) {
     analogin_reset();
 
 
+    // TODO: move this to analogout_reset()
     // Wait for the DAC to sync then reset.
     while (DAC->STATUS.reg & DAC_STATUS_SYNCBUSY) {}
     DAC->CTRLA.reg |= DAC_CTRLA_SWRST;