samd21,samd51,nrf52840: unify bootloader entry process

src/machine/machine_nrf52840_enter_bootloader.go

@@ -0,0 +1,39 @@
+//go:build nrf52840
+// +build nrf52840
+
+package machine
+
+import (
+	"device/arm"
+	"device/nrf"
+)
+
+const (
+	DFU_MAGIC_SERIAL_ONLY_RESET = 0x4e
+	DFU_MAGIC_UF2_RESET         = 0x57
+	DFU_MAGIC_OTA_RESET         = 0xA8
+)
+
+// 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()
+}