add rp2040, pico

adds preliminary support (just enough to run blinky1) for the Raspberry Pi Pico board along with the rp2040 mcu.

src/machine/machine_rp2040_resets.go

@@ -0,0 +1,43 @@
+// +build rp2040
+
+package machine
+
+import (
+	"device/rp"
+	"runtime/volatile"
+	"unsafe"
+)
+
+// RESETS_RESET_Msk is bitmask to reset all peripherals
+//
+// TODO: This field is not available in the device file.
+const RESETS_RESET_Msk = 0x01ffffff
+
+type resetsType struct {
+	reset     volatile.Register32
+	wdSel     volatile.Register32
+	resetDone volatile.Register32
+}
+
+var resets = (*resetsType)(unsafe.Pointer(rp.RESETS))
+
+// resetBlock resets hardware blocks specified
+// by the bit pattern in bits.
+func resetBlock(bits uint32) {
+	resets.reset.SetBits(bits)
+}
+
+// unresetBlock brings hardware blocks specified by the
+// bit pattern in bits out of reset.
+func unresetBlock(bits uint32) {
+	resets.reset.ClearBits(bits)
+}
+
+// unresetBlockWait brings specified hardware blocks
+// specified by the bit pattern in bits
+// out of reset and wait for completion.
+func unresetBlockWait(bits uint32) {
+	unresetBlock(bits)
+	for !resets.resetDone.HasBits(bits) {
+	}
+}