nrf: set interrupt priorities

The default priority is 0 (highest) which is reserved by the SoftDevice.
For normal operation the exact priority level doesn't matter, only the
relative priority matters. So this change makes the code compatible with
the SoftDevice without actually changing the behavior.

src/machine/machine_nrf.go

@@ -78,6 +78,7 @@ func (uart UART) Configure(config UARTConfig) {
 	nrf.UART0.INTENSET = nrf.UART_INTENSET_RXDRDY_Msk
 
 	// Enable RX IRQ.
+	arm.SetPriority(nrf.IRQ_UART0, 0xc0) // low priority
 	arm.EnableIRQ(nrf.IRQ_UART0)
 }
 

src/runtime/runtime_nrf.go

@@ -42,7 +42,7 @@ func initLFCLK() {
 
 func initRTC() {
 	nrf.RTC1.TASKS_START = 1
-	// TODO: set priority
+	arm.SetPriority(nrf.IRQ_RTC1, 0xc0) // low priority
 	arm.EnableIRQ(nrf.IRQ_RTC1)
 }