machine/nrf: implement auto-reset over USB for nrf52840

src/machine/usb_nrf52840.go

@@ -384,12 +384,6 @@ func cdcSetup(setup usbSetup) bool {
 	return false
 }
 
-func checkShouldReset() {
-	if usbLineInfo.dwDTERate == 1200 && usbLineInfo.lineState&usb_CDC_LINESTATE_DTR == 0 {
-		// TODO: reset here
-	}
-}
-
 func sendUSBPacket(ep uint32, data []byte) {
 	count := len(data)
 	copy(udd_ep_in_cache_buffer[ep][:], data)

src/machine/usb_nrf52840_reset_none.go

@@ -0,0 +1,6 @@
+// +build nrf52840,!nrf52840_reset_uf2
+
+package machine
+
+func checkShouldReset() {
+}

src/machine/usb_nrf52840_reset_uf2.go

@@ -0,0 +1,46 @@
+// +build nrf52840,nrf52840_reset_uf2
+
+package machine
+
+import (
+	"device/arm"
+	"device/nrf"
+)
+
+const (
+	DFU_MAGIC_SERIAL_ONLY_RESET = 0x4e
+	DFU_MAGIC_UF2_RESET         = 0x57
+	DFU_MAGIC_OTA_RESET         = 0xA8
+)
+
+// checkShouldReset is called by the USB-CDC implementation to check whether to
+// reset into the bootloader/OTA and if so, resets the chip appropriately.
+func checkShouldReset() {
+	if usbLineInfo.dwDTERate == 1200 && usbLineInfo.lineState&usb_CDC_LINESTATE_DTR == 0 {
+		EnterUF2Bootloader()
+	}
+}
+
+// EnterSerialBootloader resets the chip into the serial bootloader. After
+// reset, it can be flashed using serial/nrfutil.
+func EnterSerialBootloader() {
+	arm.DisableInterrupts()
+	nrf.POWER.GPREGRET.Set(DFU_MAGIC_SERIAL_ONLY_RESET)
+	arm.SystemReset()
+}
+
+// EnterUF2Bootloader resets the chip into the UF2 bootloader. After reset, it
+// can be flashed via nrfutil or by copying a UF2 file to the mass storage device
+func EnterUF2Bootloader() {
+	arm.DisableInterrupts()
+	nrf.POWER.GPREGRET.Set(DFU_MAGIC_UF2_RESET)
+	arm.SystemReset()
+}
+
+// EnterOTABootloader resets the chip into the bootloader so that it can be
+// flashed via an OTA update
+func EnterOTABootloader() {
+	arm.DisableInterrupts()
+	nrf.POWER.GPREGRET.Set(DFU_MAGIC_OTA_RESET)
+	arm.SystemReset()
+}