Add RP2350 support (#4459)

machine/rp2350: add support

* add linker scripts for rp2350
* add bootloader
* begin melding rp2040 and rp2350 APIs
* add UART
* add rp2350 boot patching
* Fix RP2350 memory layout (#4626)
* Remove rp2040-style second stage bootloader.
* Add 'minimum viable' IMAGE_DEF embedded block
* Create a pico2 specific target
* Implement rp2350 init, clock, and uart support
* Merge rp2 reset code back together
* Separate chip-specific clock definitions
* Clear pad isolation bit on rp2350
* Init UART in rp2350 runtime
* Correct usb/serial initialization order
* Implement jump-to-bootloader
* test: add pico2 to smoketests

---------

Signed-off-by: deadprogram <ron@hybridgroup.com>
Co-authored-by: Matthew Mets <matt.mets@cibomahto.com>
Co-authored-by: Matt Mets <matt@blinkinlabs.com>
Co-authored-by: deadprogram <ron@hybridgroup.com>

src/machine/machine_rp2_xosc.go

@@ -0,0 +1,47 @@
+//go:build rp2040 || rp2350
+
+package machine
+
+import (
+	"device/rp"
+	"runtime/volatile"
+	"unsafe"
+)
+
+// On some boards, the XOSC can take longer than usual to stabilize. On such
+// boards, this is needed to avoid a hard fault on boot/reset. Refer to
+// PICO_XOSC_STARTUP_DELAY_MULTIPLIER in the Pico SDK for additional details.
+const XOSC_STARTUP_DELAY_MULTIPLIER = 64
+
+type xoscType struct {
+	ctrl     volatile.Register32
+	status   volatile.Register32
+	dormant  volatile.Register32
+	startup  volatile.Register32
+	reserved [3 - 3*rp2350ExtraReg]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 * XOSC_STARTUP_DELAY_MULTIPLIER
+	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) {
+	}
+}