src/machine/machine_rp2040_xosc.go


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//go:build rp2040

package machine

import (
	"device/rp"
	"runtime/volatile"
	"unsafe"
)

type xoscType struct {
	ctrl     volatile.Register32
	status   volatile.Register32
	dormant  volatile.Register32
	startup  volatile.Register32
	reserved [3]volatile.Register32
	count    volatile.Register32
}

var xosc = (*xoscType)(unsafe.Pointer(rp.XOSC))

// init initializes the crystal oscillator system.
//
// This function will block until the crystal oscillator has stabilised.
func (osc *xoscType) init() {
	// Assumes 1-15 MHz input
	if xoscFreq > 15 {
		panic("xosc frequency cannot be greater than 15MHz")
	}
	osc.ctrl.Set(rp.XOSC_CTRL_FREQ_RANGE_1_15MHZ)

	// Set xosc startup delay
	delay := (((xoscFreq * MHz) / 1000) + 128) / 256
	osc.startup.Set(uint32(delay))

	// Set the enable bit now that we have set freq range and startup delay
	osc.ctrl.SetBits(rp.XOSC_CTRL_ENABLE_ENABLE << rp.XOSC_CTRL_ENABLE_Pos)

	// Wait for xosc to be stable
	for !osc.status.HasBits(rp.XOSC_STATUS_STABLE) {
	}
}