fix(rp2): disable DBGPAUSE on startup

Author: mikesmitty

src/machine/machine_rp2.go

@@ -58,6 +58,10 @@ func machineInit() {
 
 	// Peripheral clocks should now all be running
 	unresetBlockWait(RESETS_RESET_Msk)
+
+	// DBGPAUSE pauses the timer when a debugger is connected. This prevents
+	// sleep functions from ever returning, so disable it.
+	timer.setDbgPause(false)
 }
 
 //go:linkname ticks runtime.machineTicks

src/machine/machine_rp2_timer.go

@@ -101,3 +101,15 @@ func (tmr *timerType) lightSleep(us uint64) {
 	// Disable interrupt
 	intr.Disable()
 }
+
+// setDbgPause sets whether this timer is paused when a debugger is connected.
+func (tmr *timerType) setDbgPause(enable bool) {
+	const bitPos = 1
+	const bitMask = 0b11
+	val := uint32(0b00)
+	if enable {
+		// Disable timer when debugger is connected to either core.
+		val = 0b11
+	}
+	tmr.dbgPause.ReplaceBits(val, bitMask, bitPos)
+}