diff --git a/atmel-samd/Makefile b/atmel-samd/Makefile
index f6c183ba92..b5d2037a24 100644
--- a/atmel-samd/Makefile
+++ b/atmel-samd/Makefile
@@ -123,6 +123,7 @@ CFLAGS_CORTEX_M0 = \
 	-DI2S_CALLBACK_MODE=false \
 	-DTC_ASYNC=true \
 	-DUSB_DEVICE_LPM_SUPPORT \
+	-DCIRCUITPY_SOFTWARE_SAFE_MODE=0x0ADABEEF \
 	-DCIRCUITPY_CANARY_WORD=0xADAF00 \
 	-DCIRCUITPY_SAFE_RESTART_WORD=0xDEADBEEF \
 	--param max-inline-insns-single=500
@@ -315,6 +316,7 @@ SRC_BINDINGS_ENUMS = \
 	digitalio/Direction.c \
 	digitalio/DriveMode.c \
 	digitalio/Pull.c \
+	microcontroller/RunMode.c \
 	help.c \
 	util.c
 
diff --git a/atmel-samd/boards/samd21x18-bootloader-crystalless.ld b/atmel-samd/boards/samd21x18-bootloader-crystalless.ld
index 56ae5feb46..1d54bb88ca 100644
--- a/atmel-samd/boards/samd21x18-bootloader-crystalless.ld
+++ b/atmel-samd/boards/samd21x18-bootloader-crystalless.ld
@@ -11,7 +11,8 @@ MEMORY
 }
 
 /* top end of the stack */
-_estack = ORIGIN(RAM) + LENGTH(RAM);
+_estack = ORIGIN(RAM) + LENGTH(RAM) - 4;
+_bootloader_dbl_tap = _estack;
 
 /* define output sections */
 SECTIONS
diff --git a/atmel-samd/boards/samd21x18-bootloader-external-flash-crystalless.ld b/atmel-samd/boards/samd21x18-bootloader-external-flash-crystalless.ld
index 1c04247473..81c1e84501 100644
--- a/atmel-samd/boards/samd21x18-bootloader-external-flash-crystalless.ld
+++ b/atmel-samd/boards/samd21x18-bootloader-external-flash-crystalless.ld
@@ -11,7 +11,8 @@ MEMORY
 }
 
 /* top end of the stack */
-_estack = ORIGIN(RAM) + LENGTH(RAM);
+_estack = ORIGIN(RAM) + LENGTH(RAM) - 4;
+_bootloader_dbl_tap = _estack;
 
 /* define output sections */
 SECTIONS
diff --git a/atmel-samd/boards/samd21x18-bootloader-external-flash.ld b/atmel-samd/boards/samd21x18-bootloader-external-flash.ld
index 4346c170ce..8563ed3cb3 100644
--- a/atmel-samd/boards/samd21x18-bootloader-external-flash.ld
+++ b/atmel-samd/boards/samd21x18-bootloader-external-flash.ld
@@ -10,7 +10,8 @@ MEMORY
 }
 
 /* top end of the stack */
-_estack = ORIGIN(RAM) + LENGTH(RAM);
+_estack = ORIGIN(RAM) + LENGTH(RAM) - 4;
+_bootloader_dbl_tap = _estack;
 
 /* define output sections */
 SECTIONS
diff --git a/atmel-samd/boards/samd21x18-bootloader.ld b/atmel-samd/boards/samd21x18-bootloader.ld
index 13a3f75c18..4d2005518f 100644
--- a/atmel-samd/boards/samd21x18-bootloader.ld
+++ b/atmel-samd/boards/samd21x18-bootloader.ld
@@ -11,7 +11,8 @@ MEMORY
 }
 
 /* top end of the stack */
-_estack = ORIGIN(RAM) + LENGTH(RAM);
+_estack = ORIGIN(RAM) + LENGTH(RAM) - 4;
+_bootloader_dbl_tap = _estack;
 
 /* define output sections */
 SECTIONS
diff --git a/atmel-samd/boards/samd21x18-external-flash.ld b/atmel-samd/boards/samd21x18-external-flash.ld
index f5797cf6f5..629e190b1c 100644
--- a/atmel-samd/boards/samd21x18-external-flash.ld
+++ b/atmel-samd/boards/samd21x18-external-flash.ld
@@ -12,6 +12,7 @@ MEMORY
 
 /* top end of the stack */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_bootloader_dbl_tap = 0;
 
 /* define output sections */
 SECTIONS
diff --git a/atmel-samd/boards/samd21x18.ld b/atmel-samd/boards/samd21x18.ld
index a68094758f..9e318e9482 100644
--- a/atmel-samd/boards/samd21x18.ld
+++ b/atmel-samd/boards/samd21x18.ld
@@ -12,6 +12,7 @@ MEMORY
 
 /* top end of the stack */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_bootloader_dbl_tap = 0;
 
 /* define output sections */
 SECTIONS
diff --git a/atmel-samd/common-hal/digitalio/DigitalInOut.c b/atmel-samd/common-hal/digitalio/DigitalInOut.c
index 16654f0fe8..b14d20c2d2 100644
--- a/atmel-samd/common-hal/digitalio/DigitalInOut.c
+++ b/atmel-samd/common-hal/digitalio/DigitalInOut.c
@@ -64,7 +64,7 @@ void common_hal_digitalio_digitalinout_deinit(digitalio_digitalinout_obj_t* self
 }
 
 void common_hal_digitalio_digitalinout_switch_to_input(
-        digitalio_digitalinout_obj_t* self, enum digitalio_pull_t pull) {
+        digitalio_digitalinout_obj_t* self, digitalio_pull_t pull) {
     self->output = false;
 
     common_hal_digitalio_digitalinout_set_pull(self, pull);
@@ -72,7 +72,7 @@ void common_hal_digitalio_digitalinout_switch_to_input(
 
 void common_hal_digitalio_digitalinout_switch_to_output(
         digitalio_digitalinout_obj_t* self, bool value,
-        enum digitalio_drive_mode_t drive_mode) {
+        digitalio_drive_mode_t drive_mode) {
     struct port_config pin_conf;
     port_get_config_defaults(&pin_conf);
 
@@ -88,7 +88,7 @@ void common_hal_digitalio_digitalinout_switch_to_output(
     common_hal_digitalio_digitalinout_set_value(self, value);
 }
 
-enum digitalio_direction_t common_hal_digitalio_digitalinout_get_direction(
+digitalio_direction_t common_hal_digitalio_digitalinout_get_direction(
         digitalio_digitalinout_obj_t* self) {
     return self->output? DIRECTION_OUTPUT : DIRECTION_INPUT;
 }
@@ -131,7 +131,7 @@ bool common_hal_digitalio_digitalinout_get_value(
 
 void common_hal_digitalio_digitalinout_set_drive_mode(
         digitalio_digitalinout_obj_t* self,
-        enum digitalio_drive_mode_t drive_mode) {
+        digitalio_drive_mode_t drive_mode) {
     bool value = common_hal_digitalio_digitalinout_get_value(self);
     self->open_drain = drive_mode == DRIVE_MODE_OPEN_DRAIN;
     // True is implemented differently between modes so reset the value to make
@@ -141,7 +141,7 @@ void common_hal_digitalio_digitalinout_set_drive_mode(
     }
 }
 
-enum digitalio_drive_mode_t common_hal_digitalio_digitalinout_get_drive_mode(
+digitalio_drive_mode_t common_hal_digitalio_digitalinout_get_drive_mode(
         digitalio_digitalinout_obj_t* self) {
     if (self->open_drain) {
         return DRIVE_MODE_OPEN_DRAIN;
@@ -151,7 +151,7 @@ enum digitalio_drive_mode_t common_hal_digitalio_digitalinout_get_drive_mode(
 }
 
 void common_hal_digitalio_digitalinout_set_pull(
-        digitalio_digitalinout_obj_t* self, enum digitalio_pull_t pull) {
+        digitalio_digitalinout_obj_t* self, digitalio_pull_t pull) {
     enum port_pin_pull asf_pull = PORT_PIN_PULL_NONE;
     switch (pull) {
         case PULL_UP:
@@ -172,7 +172,7 @@ void common_hal_digitalio_digitalinout_set_pull(
     port_pin_set_config(self->pin->pin, &pin_conf);
 }
 
-enum digitalio_pull_t common_hal_digitalio_digitalinout_get_pull(
+digitalio_pull_t common_hal_digitalio_digitalinout_get_pull(
         digitalio_digitalinout_obj_t* self) {
     uint32_t pin = self->pin->pin;
     PortGroup *const port_base = port_get_group_from_gpio_pin(pin);
diff --git a/atmel-samd/common-hal/microcontroller/__init__.c b/atmel-samd/common-hal/microcontroller/__init__.c
index 84cea008b8..b90c38b604 100644
--- a/atmel-samd/common-hal/microcontroller/__init__.c
+++ b/atmel-samd/common-hal/microcontroller/__init__.c
@@ -26,10 +26,13 @@
 
 #include "py/mphal.h"
 #include "py/obj.h"
+#include "py/runtime.h"
 
+#include "reset.h"
 #include "samd21_pins.h"
 
 #include "shared-bindings/nvm/ByteArray.h"
+#include "shared-bindings/microcontroller/__init__.h"
 #include "shared-bindings/microcontroller/Processor.h"
 
 void common_hal_mcu_delay_us(uint32_t delay) {
@@ -51,9 +54,33 @@ void common_hal_mcu_enable_interrupts(void) {
     cpu_irq_restore(irq_flags);
 }
 
+extern uint32_t _ezero;
+extern uint32_t _srelocate;
+
+void common_hal_mcu_on_next_reset(mcu_runmode_t runmode) {
+    // Set up the defaults.
+    _bootloader_dbl_tap = DBL_TAP_MAGIC;
+    _ezero = CIRCUITPY_CANARY_WORD;
+
+    if (runmode == RUNMODE_BOOTLOADER) {
+        if (&_bootloader_dbl_tap < &_srelocate) {
+            mp_raise_ValueError("Cannot reset into bootloader because no bootloader is present.");
+        }
+        // Pretend to be the first of the two reset presses needed to enter the
+        // bootloader. That way one reset will end in the bootloader.
+        _bootloader_dbl_tap = DBL_TAP_MAGIC;
+    } else if (runmode == RUNMODE_SAFE_MODE) {
+        _ezero = CIRCUITPY_SOFTWARE_SAFE_MODE;
+    }
+}
+
+void common_hal_mcu_reset(void) {
+    reset();
+}
+
 // The singleton microcontroller.Processor object, bound to microcontroller.cpu
 // It currently only has properties, and no state.
-mcu_processor_obj_t common_hal_mcu_processor_obj = {
+const mcu_processor_obj_t common_hal_mcu_processor_obj = {
     .base = {
         .type = &mcu_processor_type,
     },
@@ -62,7 +89,7 @@ mcu_processor_obj_t common_hal_mcu_processor_obj = {
 // NVM is only available on Express boards for now.
 #if CIRCUITPY_INTERNAL_NVM_SIZE > 0
 // The singleton nvm.ByteArray object.
-nvm_bytearray_obj_t common_hal_mcu_nvm_obj = {
+const nvm_bytearray_obj_t common_hal_mcu_nvm_obj = {
     .base = {
         .type = &nvm_bytearray_type,
     },
diff --git a/atmel-samd/main.c b/atmel-samd/main.c
index 7bc4a87ed6..880a0e1709 100644
--- a/atmel-samd/main.c
+++ b/atmel-samd/main.c
@@ -84,6 +84,7 @@ typedef enum {
     BROWNOUT,
     HARD_CRASH,
     USER_SAFE_MODE,
+    SOFTWARE_SAFE_MODE
 } safe_mode_t;
 
 void do_str(const char *src, mp_parse_input_kind_t input_kind) {
@@ -375,7 +376,10 @@ bool start_mp(safe_mode_t safe_mode) {
                 mp_hal_stdout_tx_str(".\r\n");
             } else
             #endif
-            if (safe_mode != NO_SAFE_MODE) {
+            if (safe_mode == SOFTWARE_SAFE_MODE) {
+                mp_hal_stdout_tx_str("\r\nYou requested starting in safe mode from your software.");
+                mp_hal_stdout_tx_str(".\r\nTo exit, please reset the board.\r\n");
+            } else if (safe_mode != NO_SAFE_MODE) {
                 mp_hal_stdout_tx_str("\r\nYou are running in safe mode which means something really bad happened.\r\n");
                 if (safe_mode == HARD_CRASH) {
                     mp_hal_stdout_tx_str("Looks like our core CircuitPython code crashed hard. Whoops!\r\n");
@@ -524,10 +528,14 @@ safe_mode_t samd21_init(void) {
     REG_MTB_MASTER = 0x00000000 + 6;
 #endif
 
+    // CIRCUITPY_SOFTWARE_SAFE_MODE works just like the canary except if it
+    // survives we enter safe mode with a friendlier message.
+    bool software_safe_mode = _ezero == CIRCUITPY_SOFTWARE_SAFE_MODE;
+
 // On power on start or external reset, set _ezero to the canary word. If it
-// gets killed, we boot in safe mod. _ezero is the boundary between statically
-// allocated memory including the fixed MicroPython heap and the stack. If either
-// misbehaves, the canary will not be in tact after soft reset.
+// gets killed, we boot in safe mode. _ezero is the boundary between statically
+// allocated memory including the fixed MicroPython heap and the stack. If
+// either misbehaves, the canary will not be intact after soft reset.
 #ifdef CIRCUITPY_CANARY_WORD
     if (PM->RCAUSE.bit.POR == 1 || PM->RCAUSE.bit.EXT == 1) {
         _ezero = CIRCUITPY_CANARY_WORD;
@@ -607,6 +615,10 @@ safe_mode_t samd21_init(void) {
         return USER_SAFE_MODE;
     }
 
+    if (software_safe_mode) {
+        return SOFTWARE_SAFE_MODE;
+    }
+
     #if CIRCUITPY_INTERNAL_NVM_SIZE > 0
     // Upgrade the nvm flash to include one sector for eeprom emulation.
     struct nvm_fusebits fuses;
diff --git a/atmel-samd/mphalport.c b/atmel-samd/mphalport.c
index c1aebe08a4..4d597be6b2 100644
--- a/atmel-samd/mphalport.c
+++ b/atmel-samd/mphalport.c
@@ -62,7 +62,7 @@ volatile bool reset_on_disconnect = false;
 
 void usb_dtr_notify(uint8_t port, bool set) {
     mp_cdc_enabled = set;
-    if (!set && reset_on_disconnect) {
+    if (!set && reset_on_disconnect && _bootloader_dbl_tap != 0) {
         reset_to_bootloader();
     }
 }
diff --git a/atmel-samd/reset.c b/atmel-samd/reset.c
index 442774a5f4..822789b472 100644
--- a/atmel-samd/reset.c
+++ b/atmel-samd/reset.c
@@ -29,12 +29,12 @@
 
 #include "asf/sam0/utils/cmsis/samd21/include/samd21.h"
 
-// Copied from inc/uf2.h in https://github.com/Microsoft/uf2-samd21
-#define DBL_TAP_PTR ((volatile uint32_t *)(HMCRAMC0_ADDR + HMCRAMC0_SIZE - 4))
-#define DBL_TAP_MAGIC 0xf01669ef // Randomly selected, adjusted to have first and last bit set
-
-void reset_to_bootloader(void) {
+void reset(void) {
     flash_flush();
-    *DBL_TAP_PTR = DBL_TAP_MAGIC;
     NVIC_SystemReset();
 }
+
+void reset_to_bootloader(void) {
+    _bootloader_dbl_tap = DBL_TAP_MAGIC;
+    reset();
+}
diff --git a/atmel-samd/reset.h b/atmel-samd/reset.h
index 88140f3b83..00b2312bb7 100644
--- a/atmel-samd/reset.h
+++ b/atmel-samd/reset.h
@@ -26,6 +26,12 @@
 #ifndef MICROPY_INCLUDED_ATMEL_SAMD_RESET_H
 #define MICROPY_INCLUDED_ATMEL_SAMD_RESET_H
 
+// Copied from inc/uf2.h in https://github.com/Microsoft/uf2-samd21
+#define DBL_TAP_MAGIC 0xf01669ef // Randomly selected, adjusted to have first and last bit set
+
+extern uint32_t _bootloader_dbl_tap;
+
 void reset_to_bootloader(void);
+void reset(void);
 
 #endif  // MICROPY_INCLUDED_ATMEL_SAMD_RESET_H
diff --git a/esp8266/Makefile b/esp8266/Makefile
index bfaefb4651..d177bee58c 100644
--- a/esp8266/Makefile
+++ b/esp8266/Makefile
@@ -128,6 +128,7 @@ SRC_BINDINGS_ENUMS = \
 	digitalio/Direction.c \
 	digitalio/DriveMode.c \
 	digitalio/Pull.c \
+	microcontroller/RunMode.c \
 	util.c
 
 SRC_COMMON_HAL_EXPANDED = $(addprefix shared-bindings/, $(SRC_COMMON_HAL)) \
diff --git a/esp8266/common-hal/digitalio/DigitalInOut.c b/esp8266/common-hal/digitalio/DigitalInOut.c
index 70ed207d59..7101e64145 100644
--- a/esp8266/common-hal/digitalio/DigitalInOut.c
+++ b/esp8266/common-hal/digitalio/DigitalInOut.c
@@ -59,7 +59,7 @@ void common_hal_digitalio_digitalinout_deinit(digitalio_digitalinout_obj_t* self
 }
 
 void common_hal_digitalio_digitalinout_switch_to_input(
-        digitalio_digitalinout_obj_t* self, enum digitalio_pull_t pull) {
+        digitalio_digitalinout_obj_t* self, digitalio_pull_t pull) {
     self->output = false;
 
     if (self->pin->gpio_number == 16) {
@@ -75,7 +75,7 @@ void common_hal_digitalio_digitalinout_switch_to_input(
 
 void common_hal_digitalio_digitalinout_switch_to_output(
         digitalio_digitalinout_obj_t* self, bool value,
-        enum digitalio_drive_mode_t drive_mode) {
+        digitalio_drive_mode_t drive_mode) {
     self->output = true;
     self->open_drain = drive_mode == DRIVE_MODE_OPEN_DRAIN;
     if (self->pin->gpio_number == 16) {
@@ -89,7 +89,7 @@ void common_hal_digitalio_digitalinout_switch_to_output(
     common_hal_digitalio_digitalinout_set_value(self, value);
 }
 
-enum digitalio_direction_t common_hal_digitalio_digitalinout_get_direction(
+digitalio_direction_t common_hal_digitalio_digitalinout_get_direction(
         digitalio_digitalinout_obj_t* self) {
     return self->output? DIRECTION_OUTPUT : DIRECTION_INPUT;
 }
@@ -136,7 +136,7 @@ bool common_hal_digitalio_digitalinout_get_value(
 
 void common_hal_digitalio_digitalinout_set_drive_mode(
         digitalio_digitalinout_obj_t* self,
-        enum digitalio_drive_mode_t drive_mode) {
+        digitalio_drive_mode_t drive_mode) {
     bool value = common_hal_digitalio_digitalinout_get_value(self);
     self->open_drain = drive_mode == DRIVE_MODE_OPEN_DRAIN;
     // True is implemented differently between modes so reset the value to make
@@ -146,7 +146,7 @@ void common_hal_digitalio_digitalinout_set_drive_mode(
     }
 }
 
-enum digitalio_drive_mode_t common_hal_digitalio_digitalinout_get_drive_mode(
+digitalio_drive_mode_t common_hal_digitalio_digitalinout_get_drive_mode(
         digitalio_digitalinout_obj_t* self) {
     if (self->open_drain) {
         return DRIVE_MODE_OPEN_DRAIN;
@@ -156,7 +156,7 @@ enum digitalio_drive_mode_t common_hal_digitalio_digitalinout_get_drive_mode(
 }
 
 void common_hal_digitalio_digitalinout_set_pull(
-        digitalio_digitalinout_obj_t* self, enum digitalio_pull_t pull) {
+        digitalio_digitalinout_obj_t* self, digitalio_pull_t pull) {
     if (pull == PULL_DOWN) {
         nlr_raise(mp_obj_new_exception_msg(&mp_type_OSError,
             "ESP8266 does not support pull down."));
@@ -174,7 +174,7 @@ void common_hal_digitalio_digitalinout_set_pull(
     }
 }
 
-enum digitalio_pull_t common_hal_digitalio_digitalinout_get_pull(
+digitalio_pull_t common_hal_digitalio_digitalinout_get_pull(
         digitalio_digitalinout_obj_t* self) {
     if (self->pin->gpio_number < 16 &&
         (READ_PERI_REG(self->pin->peripheral) & PERIPHS_IO_MUX_PULLUP) != 0) {
diff --git a/esp8266/common-hal/microcontroller/__init__.c b/esp8266/common-hal/microcontroller/__init__.c
index 6aef23761c..6d446ceacb 100644
--- a/esp8266/common-hal/microcontroller/__init__.c
+++ b/esp8266/common-hal/microcontroller/__init__.c
@@ -24,9 +24,12 @@
  * THE SOFTWARE.
  */
 
+#include "py/runtime.h"
+
 #include "common-hal/microcontroller/Pin.h"
 #include "common-hal/microcontroller/Processor.h"
 
+#include "shared-bindings/microcontroller/__init__.h"
 #include "shared-bindings/microcontroller/Pin.h"
 #include "shared-bindings/microcontroller/Processor.h"
 
@@ -34,6 +37,7 @@
 #include "ets_alt_task.h"
 #include "etshal.h"
 #include "osapi.h"
+#include "user_interface.h"
 #include "xtirq.h"
 
 #define ETS_LOOP_ITER_BIT (12)
@@ -54,9 +58,21 @@ void common_hal_mcu_enable_interrupts() {
     enable_irq(saved_interrupt_state & ~(1 << ETS_LOOP_ITER_BIT));
 }
 
+void common_hal_mcu_on_next_reset(mcu_runmode_t runmode) {
+    if (runmode == RUNMODE_BOOTLOADER) {
+        mp_raise_ValueError("Cannot reset into bootloader because no bootloader is present.");
+    } else if (runmode == RUNMODE_SAFE_MODE) {
+        mp_raise_ValueError("ESP8226 does not support safe mode.");
+    }
+}
+
+void common_hal_mcu_reset(void) {
+    system_restart();
+}
+
 // The singleton microcontroller.Processor object, returned by microcontroller.cpu
 // It currently only has properties, and no state.
-mcu_processor_obj_t common_hal_mcu_processor_obj = {
+const mcu_processor_obj_t common_hal_mcu_processor_obj = {
     .base = {
         .type = &mcu_processor_type,
     },
diff --git a/shared-bindings/digitalio/DigitalInOut.c b/shared-bindings/digitalio/DigitalInOut.c
index ea2ba0b893..008883b8bd 100644
--- a/shared-bindings/digitalio/DigitalInOut.c
+++ b/shared-bindings/digitalio/DigitalInOut.c
@@ -124,7 +124,7 @@ STATIC mp_obj_t digitalio_digitalinout_switch_to_output(size_t n_args, const mp_
     mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
     mp_arg_parse_all(n_args - 1, pos_args + 1, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
 
-    enum digitalio_drive_mode_t drive_mode = DRIVE_MODE_PUSH_PULL;
+    digitalio_drive_mode_t drive_mode = DRIVE_MODE_PUSH_PULL;
     if (args[ARG_drive_mode].u_rom_obj == &digitalio_drive_mode_open_drain_obj) {
         drive_mode = DRIVE_MODE_OPEN_DRAIN;
     }
@@ -161,7 +161,7 @@ STATIC mp_obj_t digitalio_digitalinout_switch_to_input(size_t n_args, const mp_o
     mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
     mp_arg_parse_all(n_args - 1, pos_args + 1, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
 
-    enum digitalio_pull_t pull = PULL_NONE;
+    digitalio_pull_t pull = PULL_NONE;
     if (args[ARG_pull].u_rom_obj == &digitalio_pull_up_obj) {
         pull = PULL_UP;
     }else if (args[ARG_pull].u_rom_obj == &digitalio_pull_down_obj) {
@@ -191,7 +191,7 @@ extern const digitalio_digitalio_direction_obj_t digitalio_digitalio_direction_o
 STATIC mp_obj_t digitalio_digitalinout_obj_get_direction(mp_obj_t self_in) {
     digitalio_digitalinout_obj_t *self = MP_OBJ_TO_PTR(self_in);
     raise_error_if_deinited(common_hal_digitalio_digitalinout_deinited(self));
-    enum digitalio_direction_t direction = common_hal_digitalio_digitalinout_get_direction(self);
+    digitalio_direction_t direction = common_hal_digitalio_digitalinout_get_direction(self);
     if (direction == DIRECTION_INPUT) {
         return (mp_obj_t)&digitalio_direction_input_obj;
     }
@@ -262,7 +262,7 @@ STATIC mp_obj_t digitalio_digitalinout_obj_get_drive_mode(mp_obj_t self_in) {
         mp_raise_AttributeError("Drive mode not used when direction is input.");
         return mp_const_none;
     }
-    enum digitalio_drive_mode_t drive_mode = common_hal_digitalio_digitalinout_get_drive_mode(self);
+    digitalio_drive_mode_t drive_mode = common_hal_digitalio_digitalinout_get_drive_mode(self);
     if (drive_mode == DRIVE_MODE_PUSH_PULL) {
         return (mp_obj_t)&digitalio_drive_mode_push_pull_obj;
     }
@@ -277,7 +277,7 @@ STATIC mp_obj_t digitalio_digitalinout_obj_set_drive_mode(mp_obj_t self_in, mp_o
         mp_raise_AttributeError("Drive mode not used when direction is input.");
         return mp_const_none;
     }
-    enum digitalio_drive_mode_t c_drive_mode = DRIVE_MODE_PUSH_PULL;
+    digitalio_drive_mode_t c_drive_mode = DRIVE_MODE_PUSH_PULL;
     if (drive_mode == &digitalio_drive_mode_open_drain_obj) {
         c_drive_mode = DRIVE_MODE_OPEN_DRAIN;
     }
@@ -307,7 +307,7 @@ STATIC mp_obj_t digitalio_digitalinout_obj_get_pull(mp_obj_t self_in) {
         mp_raise_AttributeError("Pull not used when direction is output.");
         return mp_const_none;
     }
-    enum digitalio_pull_t pull = common_hal_digitalio_digitalinout_get_pull(self);
+    digitalio_pull_t pull = common_hal_digitalio_digitalinout_get_pull(self);
     if (pull == PULL_UP) {
         return (mp_obj_t)&digitalio_pull_up_obj;
     } else if (pull == PULL_DOWN) {
@@ -324,7 +324,7 @@ STATIC mp_obj_t digitalio_digitalinout_obj_set_pull(mp_obj_t self_in, mp_obj_t p
         mp_raise_AttributeError("Pull not used when direction is output.");
         return mp_const_none;
     }
-    enum digitalio_pull_t pull = PULL_NONE;
+    digitalio_pull_t pull = PULL_NONE;
     if (pull_obj == &digitalio_pull_up_obj) {
         pull = PULL_UP;
     } else if (pull_obj == &digitalio_pull_down_obj) {
diff --git a/shared-bindings/digitalio/DigitalInOut.h b/shared-bindings/digitalio/DigitalInOut.h
index 74970881b8..2aaa31b7f4 100644
--- a/shared-bindings/digitalio/DigitalInOut.h
+++ b/shared-bindings/digitalio/DigitalInOut.h
@@ -43,14 +43,14 @@ typedef enum {
 digitalinout_result_t common_hal_digitalio_digitalinout_construct(digitalio_digitalinout_obj_t* self, const mcu_pin_obj_t* pin);
 void common_hal_digitalio_digitalinout_deinit(digitalio_digitalinout_obj_t* self);
 bool common_hal_digitalio_digitalinout_deinited(digitalio_digitalinout_obj_t* self);
-void common_hal_digitalio_digitalinout_switch_to_input(digitalio_digitalinout_obj_t* self, enum digitalio_pull_t pull);
-void common_hal_digitalio_digitalinout_switch_to_output(digitalio_digitalinout_obj_t* self, bool value, enum digitalio_drive_mode_t drive_mode);
-enum digitalio_direction_t common_hal_digitalio_digitalinout_get_direction(digitalio_digitalinout_obj_t* self);
+void common_hal_digitalio_digitalinout_switch_to_input(digitalio_digitalinout_obj_t* self, digitalio_pull_t pull);
+void common_hal_digitalio_digitalinout_switch_to_output(digitalio_digitalinout_obj_t* self, bool value, digitalio_drive_mode_t drive_mode);
+digitalio_direction_t common_hal_digitalio_digitalinout_get_direction(digitalio_digitalinout_obj_t* self);
 void common_hal_digitalio_digitalinout_set_value(digitalio_digitalinout_obj_t* self, bool value);
 bool common_hal_digitalio_digitalinout_get_value(digitalio_digitalinout_obj_t* self);
-void common_hal_digitalio_digitalinout_set_drive_mode(digitalio_digitalinout_obj_t* self, enum digitalio_drive_mode_t drive_mode);
-enum digitalio_drive_mode_t common_hal_digitalio_digitalinout_get_drive_mode(digitalio_digitalinout_obj_t* self);
-void common_hal_digitalio_digitalinout_set_pull(digitalio_digitalinout_obj_t* self, enum digitalio_pull_t pull);
-enum digitalio_pull_t common_hal_digitalio_digitalinout_get_pull(digitalio_digitalinout_obj_t* self);
+void common_hal_digitalio_digitalinout_set_drive_mode(digitalio_digitalinout_obj_t* self, digitalio_drive_mode_t drive_mode);
+digitalio_drive_mode_t common_hal_digitalio_digitalinout_get_drive_mode(digitalio_digitalinout_obj_t* self);
+void common_hal_digitalio_digitalinout_set_pull(digitalio_digitalinout_obj_t* self, digitalio_pull_t pull);
+digitalio_pull_t common_hal_digitalio_digitalinout_get_pull(digitalio_digitalinout_obj_t* self);
 
 #endif // MICROPY_INCLUDED_SHARED_BINDINGS_DIGITALIO_DIGITALINOUT_H
diff --git a/shared-bindings/digitalio/Direction.h b/shared-bindings/digitalio/Direction.h
index e8fbf181d2..d71f48c2ed 100644
--- a/shared-bindings/digitalio/Direction.h
+++ b/shared-bindings/digitalio/Direction.h
@@ -29,10 +29,10 @@
 
 #include "py/obj.h"
 
-enum digitalio_direction_t {
+typedef enum {
     DIRECTION_INPUT,
     DIRECTION_OUTPUT
-};
+} digitalio_direction_t;
 typedef struct {
     mp_obj_base_t base;
 } digitalio_direction_obj_t;
diff --git a/shared-bindings/digitalio/DriveMode.h b/shared-bindings/digitalio/DriveMode.h
index 959885b1b9..47d036b3ae 100644
--- a/shared-bindings/digitalio/DriveMode.h
+++ b/shared-bindings/digitalio/DriveMode.h
@@ -29,10 +29,10 @@
 
 #include "py/obj.h"
 
-enum digitalio_drive_mode_t {
+typedef enum {
     DRIVE_MODE_PUSH_PULL,
     DRIVE_MODE_OPEN_DRAIN
-};
+} digitalio_drive_mode_t;
 
 typedef struct {
     mp_obj_base_t base;
diff --git a/shared-bindings/digitalio/Pull.h b/shared-bindings/digitalio/Pull.h
index 8c88d8673e..22fb6cd0e7 100644
--- a/shared-bindings/digitalio/Pull.h
+++ b/shared-bindings/digitalio/Pull.h
@@ -29,11 +29,11 @@
 
 #include "py/obj.h"
 
-enum digitalio_pull_t {
+typedef enum _digitalio_pull_t {
     PULL_NONE,
     PULL_UP,
     PULL_DOWN
-};
+} digitalio_pull_t;
 
 const mp_obj_type_t digitalio_pull_type;
 
diff --git a/shared-bindings/microcontroller/RunMode.c b/shared-bindings/microcontroller/RunMode.c
new file mode 100644
index 0000000000..b27a3c0909
--- /dev/null
+++ b/shared-bindings/microcontroller/RunMode.c
@@ -0,0 +1,90 @@
+/*
+ * This file is part of the Micro Python project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2017 Scott Shawcroft for Adafruit Industries
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "shared-bindings/microcontroller/RunMode.h"
+
+//| .. currentmodule:: microcontroller
+//|
+//| :class:`RunMode` -- run state of the microcontroller
+//| =============================================================
+//|
+//| .. class:: microcontroller.RunMode
+//|
+//|     Enum-like class to define the run mode of the microcontroller and
+//|     CircuitPython.
+//|
+//|     .. data:: NORMAL
+//|
+//|       Run CircuitPython as normal.
+//|
+//|     .. data:: SAFE_MODE
+//|
+//|       Run CircuitPython in safe mode. User code will not be run and the
+//|       file system will be writeable over USB.
+//|
+//|     .. data:: BOOTLOADER
+//|
+//|       Run the bootloader.
+//|
+const mp_obj_type_t mcu_runmode_type;
+
+const mcu_runmode_obj_t mcu_runmode_normal_obj = {
+    { &mcu_runmode_type },
+};
+
+const mcu_runmode_obj_t mcu_runmode_safe_mode_obj = {
+    { &mcu_runmode_type },
+};
+
+const mcu_runmode_obj_t mcu_runmode_bootloader_obj = {
+    { &mcu_runmode_type },
+};
+
+STATIC const mp_rom_map_elem_t mcu_runmode_locals_dict_table[] = {
+    {MP_ROM_QSTR(MP_QSTR_NORMAL),     MP_ROM_PTR(&mcu_runmode_normal_obj)},
+    {MP_ROM_QSTR(MP_QSTR_SAFE_MODE),  MP_ROM_PTR(&mcu_runmode_safe_mode_obj)},
+    {MP_ROM_QSTR(MP_QSTR_BOOTLOADER), MP_ROM_PTR(&mcu_runmode_bootloader_obj)},
+};
+STATIC MP_DEFINE_CONST_DICT(mcu_runmode_locals_dict, mcu_runmode_locals_dict_table);
+
+STATIC void mcu_runmode_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_t kind) {
+    qstr runmode = MP_QSTR_NORMAL;
+    if (MP_OBJ_TO_PTR(self_in) == MP_ROM_PTR(&mcu_runmode_safe_mode_obj)) {
+        runmode = MP_QSTR_SAFE_MODE;
+    } else if (MP_OBJ_TO_PTR(self_in) ==
+               MP_ROM_PTR(&mcu_runmode_bootloader_obj)) {
+        runmode = MP_QSTR_SAFE_MODE;
+    }
+    mp_printf(print, "%q.%q.%q", MP_QSTR_microcontroller, MP_QSTR_RunMode,
+              runmode);
+}
+
+const mp_obj_type_t mcu_runmode_type = {
+    { &mp_type_type },
+    .name = MP_QSTR_RunMode,
+    .print = mcu_runmode_print,
+    .locals_dict = (mp_obj_t)&mcu_runmode_locals_dict,
+};
diff --git a/shared-bindings/microcontroller/RunMode.h b/shared-bindings/microcontroller/RunMode.h
new file mode 100644
index 0000000000..5e8b6e6465
--- /dev/null
+++ b/shared-bindings/microcontroller/RunMode.h
@@ -0,0 +1,47 @@
+/*
+ * This file is part of the Micro Python project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2017 Scott Shawcroft for Adafruit Industries
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#ifndef MICROPY_INCLUDED_SHARED_BINDINGS_MICROCONTROLLER_RUNMODE_H
+#define MICROPY_INCLUDED_SHARED_BINDINGS_MICROCONTROLLER_RUNMODE_H
+
+#include "py/obj.h"
+
+typedef enum {
+    RUNMODE_NORMAL,
+    RUNMODE_SAFE_MODE,
+    RUNMODE_BOOTLOADER
+} mcu_runmode_t;
+
+const mp_obj_type_t mcu_runmode_type;
+
+typedef struct {
+    mp_obj_base_t base;
+} mcu_runmode_obj_t;
+extern const mcu_runmode_obj_t mcu_runmode_normal_obj;
+extern const mcu_runmode_obj_t mcu_runmode_safe_mode_obj;
+extern const mcu_runmode_obj_t mcu_runmode_bootloader_obj;
+
+#endif // MICROPY_INCLUDED_SHARED_BINDINGS_MICROCONTROLLER_RUNMODE_H
diff --git a/shared-bindings/microcontroller/__init__.c b/shared-bindings/microcontroller/__init__.c
index d2567bd65a..cc091591f4 100644
--- a/shared-bindings/microcontroller/__init__.c
+++ b/shared-bindings/microcontroller/__init__.c
@@ -102,6 +102,47 @@ STATIC mp_obj_t mcu_enable_interrupts(void) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_0(mcu_enable_interrupts_obj, mcu_enable_interrupts);
 
+//| .. method:: on_next_reset(run_mode)
+//|
+//|   Configure the run mode used the next time the microcontroller is reset but
+//|   not powered down.
+//|
+//|   :param ~microcontroller.RunMode run_mode: The next run mode
+//|
+STATIC mp_obj_t mcu_on_next_reset(mp_obj_t run_mode_obj) {
+    mcu_runmode_t run_mode;
+    if (run_mode_obj == &mcu_runmode_normal_obj) {
+        run_mode = RUNMODE_NORMAL;
+    } else if (run_mode_obj == &mcu_runmode_safe_mode_obj) {
+        run_mode = RUNMODE_SAFE_MODE;
+    } else if (run_mode_obj == &mcu_runmode_bootloader_obj) {
+        run_mode = RUNMODE_BOOTLOADER;
+    } else {
+        mp_raise_ValueError("Invalid run mode.");
+    }
+
+    common_hal_mcu_on_next_reset(run_mode);
+
+    return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(mcu_on_next_reset_obj, mcu_on_next_reset);
+
+//| .. method:: reset()
+//|
+//|   Reset the microcontroller. After reset, the microcontroller will enter the
+//|   run mode last set by `one_next_reset`.
+//|
+//|   .. warning:: This may result in file system corruption when connected to a
+//|     host computer. Be very careful when calling this! Make sure the device
+//|     "Safely removed" on Windows or "ejected" on Mac OSX and Linux.
+//|
+STATIC mp_obj_t mcu_reset(void) {
+    common_hal_mcu_reset();
+    // We won't actually get here because we're resetting.
+    return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_0(mcu_reset_obj, mcu_reset);
+
 //| .. attribute:: nvm
 //|
 //|   Available non-volatile memory.
@@ -128,11 +169,14 @@ STATIC const mp_rom_map_elem_t mcu_module_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR_delay_us), MP_ROM_PTR(&mcu_delay_us_obj) },
     { MP_ROM_QSTR(MP_QSTR_disable_interrupts), MP_ROM_PTR(&mcu_disable_interrupts_obj) },
     { MP_ROM_QSTR(MP_QSTR_enable_interrupts), MP_ROM_PTR(&mcu_enable_interrupts_obj) },
+    { MP_ROM_QSTR(MP_QSTR_on_next_reset), MP_ROM_PTR(&mcu_on_next_reset_obj) },
+    { MP_ROM_QSTR(MP_QSTR_reset), MP_ROM_PTR(&mcu_reset_obj) },
     #if CIRCUITPY_INTERNAL_NVM_SIZE > 0
     { MP_ROM_QSTR(MP_QSTR_nvm),  MP_ROM_PTR(&common_hal_mcu_nvm_obj) },
     #else
     { MP_ROM_QSTR(MP_QSTR_nvm),  MP_ROM_PTR(&mp_const_none_obj) },
     #endif
+    { MP_ROM_QSTR(MP_QSTR_RunMode),  MP_ROM_PTR(&mcu_runmode_type) },
     { MP_ROM_QSTR(MP_QSTR_Pin),  MP_ROM_PTR(&mcu_pin_type) },
     { MP_ROM_QSTR(MP_QSTR_pin),  MP_ROM_PTR(&mcu_pin_module) },
     { MP_ROM_QSTR(MP_QSTR_Processor),   MP_ROM_PTR(&mcu_processor_type) },
diff --git a/shared-bindings/microcontroller/__init__.h b/shared-bindings/microcontroller/__init__.h
index d43db4bf45..e1487c555a 100644
--- a/shared-bindings/microcontroller/__init__.h
+++ b/shared-bindings/microcontroller/__init__.h
@@ -33,11 +33,16 @@
 
 #include "common-hal/microcontroller/Processor.h"
 
+#include "shared-bindings/microcontroller/RunMode.h"
+
 extern void common_hal_mcu_delay_us(uint32_t);
 
 extern void common_hal_mcu_disable_interrupts(void);
 extern void common_hal_mcu_enable_interrupts(void);
 
+extern void common_hal_mcu_on_next_reset(mcu_runmode_t runmode);
+extern void common_hal_mcu_reset(void);
+
 extern const mp_obj_dict_t mcu_pin_globals;
 
 extern const mcu_processor_obj_t common_hal_mcu_processor_obj;