all: move Register{8,16,32} values into runtime/volatile

This avoids duplication of code. None of the smoke tests have changed
their output.

src/machine/machine_atmega.go

@@ -4,6 +4,7 @@ package machine
 
 import (
 	"device/avr"
+	"runtime/volatile"
 )
 
 // Configure sets the pin to input or output.
@@ -34,7 +35,7 @@ func (p Pin) Get() bool {
 	}
 }
 
-func (p Pin) getPortMask() (*avr.Register8, uint8) {
+func (p Pin) getPortMask() (*volatile.Register8, uint8) {
 	if p < 8 {
 		return avr.PORTD, 1 << uint8(p)
 	} else {

src/machine/machine_attiny.go

@@ -4,6 +4,7 @@ package machine
 
 import (
 	"device/avr"
+	"runtime/volatile"
 )
 
 // Configure sets the pin to input or output.
@@ -15,7 +16,7 @@ func (p Pin) Configure(config PinConfig) {
 	}
 }
 
-func (p Pin) getPortMask() (*avr.Register8, uint8) {
+func (p Pin) getPortMask() (*volatile.Register8, uint8) {
 	return avr.PORTB, 1 << uint8(p)
 }
 

src/machine/machine_avr.go

@@ -4,6 +4,7 @@ package machine
 
 import (
 	"device/avr"
+	"runtime/volatile"
 )
 
 type PinMode uint8
@@ -30,7 +31,7 @@ func (p Pin) Set(value bool) {
 // Warning: there are no separate pin set/clear registers on the AVR. The
 // returned mask is only valid as long as no other pin in the same port has been
 // changed.
-func (p Pin) PortMaskSet() (*avr.Register8, uint8) {
+func (p Pin) PortMaskSet() (*volatile.Register8, uint8) {
 	port, mask := p.getPortMask()
 	return port, port.Get() | mask
 }
@@ -41,7 +42,7 @@ func (p Pin) PortMaskSet() (*avr.Register8, uint8) {
 // Warning: there are no separate pin set/clear registers on the AVR. The
 // returned mask is only valid as long as no other pin in the same port has been
 // changed.
-func (p Pin) PortMaskClear() (*avr.Register8, uint8) {
+func (p Pin) PortMaskClear() (*volatile.Register8, uint8) {
 	port, mask := p.getPortMask()
 	return port, port.Get() &^ mask
 }

src/machine/usb.go

@@ -4,9 +4,9 @@ package machine
 
 import (
 	"bytes"
-	"device/sam"
 	"encoding/binary"
 	"errors"
+	"runtime/volatile"
 )
 
 const deviceDescriptorSize = 18
@@ -484,11 +484,11 @@ const (
 // 		 RoReg8                    Reserved1[0x5];
 //   } UsbDeviceDescBank;
 type usbDeviceDescBank struct {
-	ADDR      sam.Register32
-	PCKSIZE   sam.Register32
-	EXTREG    sam.Register16
-	STATUS_BK sam.Register8
-	_reserved [5]sam.Register8
+	ADDR      volatile.Register32
+	PCKSIZE   volatile.Register32
+	EXTREG    volatile.Register16
+	STATUS_BK volatile.Register8
+	_reserved [5]volatile.Register8
 }
 
 type usbDeviceDescriptor struct {