add E.rebootToUF2() for entering UF2 bootloader mode

on devices that have such a bootloader

the device will reappear as a usb drive

ChangeLog

@@ -1,5 +1,6 @@
           : nRF5x: ensure TIMER1_IRQHandler doesn't always wake idle loop up (fix #1900)
             XiaoBLE: add board: Seeed XIAO BLE
+            Add E.rebootToUF2() for entering UF2 bootloader mode (on boards that have such a bootloader)
 
      2v25 : ESP32C3: Get analogRead working correctly
             Graphics: Adjust image alignment when rotating images to avoid cropping (fix #2535)

src/jshardware.h

@@ -413,6 +413,11 @@ void jshReboot();
 void jshRebootToDFU();
 #endif
 
+#ifdef ESPR_HAS_BOOTLOADER_UF2
+/// Reboot to the UF2 bootloader. Device will reappear as a USB drive.
+void jshRebootToUF2Bootloader();
+#endif
+
 #if JSH_PORTV_COUNT>0
 /// handler for virtual ports (eg. pins on an IO Expander). This should be defined for each type of board used
 void jshVirtualPinInitialise();

src/jswrap_espruino.c

@@ -2379,6 +2379,26 @@ void jswrap_espruino_rebootToDFU() {
 #endif
 }
 
+/*JSON{
+  "type" : "staticmethod",
+  "ifdef" : "ESPR_HAS_BOOTLOADER_UF2",
+  "class" : "E",
+  "name" : "rebootToUF2",
+  "generate" : "jswrap_espruino_rebootToUF2"
+}
+Forces a hard reboot of the microcontroller into the UF2 bootloader.
+
+**Note:** The device will stay in bootloader mode until it is power-cycled or reset.
+*/
+void jswrap_espruino_rebootToUF2() {
+#ifdef ESPR_HAS_BOOTLOADER_UF2
+  jsiKill();
+  jsvKill();
+  jshKill();
+  jshRebootToUF2Bootloader();
+#endif
+}
+
 // ----------------------------------------- USB Specific Stuff
 
 #ifdef USE_USB_HID

src/jswrap_espruino.h

@@ -74,6 +74,7 @@ void jswrap_espruino_asm(JsVar *callspec, JsVar *args);
 void jswrap_espruino_compiledC(JsVar *code);
 void jswrap_espruino_reboot();
 void jswrap_espruino_rebootToDFU();
+void jswrap_espruino_rebootToUF2();
 
 void jswrap_espruino_setUSBHID(JsVar *arr);
 bool jswrap_espruino_sendUSBHID(JsVar *arr);

targets/nrf5x/jshardware.c

@@ -2887,6 +2887,14 @@ void jshReboot() {
   NVIC_SystemReset();
 }
 
+#ifdef ESPR_HAS_BOOTLOADER_UF2
+void jshRebootToUF2Bootloader() {
+  enum { DFU_MAGIC_UF2_RESET = 0x57 };
+  nrf_power_gpregret_set(DFU_MAGIC_UF2_RESET);
+  NVIC_SystemReset();
+}
+#endif
+
 /* Adds the estimated power usage of the microcontroller in uA to the 'devices' object. The CPU should be called 'CPU' */
 void jsvGetProcessorPowerUsage(JsVar *devices) {
   // draws 4mA flat out, 3uA nothing otherwise