Fix 1200 baud reset.

atmel-samd/common-hal/microcontroller/__init__.c

@@ -55,15 +55,14 @@ void common_hal_mcu_enable_interrupts(void) {
 }
 
 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) {
+        if (!bootloader_available()) {
             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

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 && _bootloader_dbl_tap != 0) {
+    if (!set && reset_on_disconnect && bootloader_available()) {
         reset_to_bootloader();
     }
 }

atmel-samd/reset.c

@@ -38,3 +38,8 @@ void reset_to_bootloader(void) {
     _bootloader_dbl_tap = DBL_TAP_MAGIC;
     reset();
 }
+
+extern uint32_t _srelocate;
+bool bootloader_available(void) {
+    return &_bootloader_dbl_tap >= &_srelocate;
+}

atmel-samd/reset.h

@@ -33,5 +33,6 @@ extern uint32_t _bootloader_dbl_tap;
 
 void reset_to_bootloader(void);
 void reset(void);
+bool bootloader_available(void);
 
 #endif  // MICROPY_INCLUDED_ATMEL_SAMD_RESET_H