Added Break implementation for windows

serial_windows.go

@@ -382,7 +382,17 @@ func (port *windowsPort) SetReadTimeout(timeout time.Duration) error {
 }
 
 func (port *windowsPort) Break(d time.Duration) error {
-	return &PortError{code: FunctionNotImplemented}
+	if err := setCommBreak(port.handle); err != nil {
+		return &PortError{causedBy: err}
+	}
+
+	time.Sleep(d)
+
+	if err := clearCommBreak(port.handle); err != nil {
+		return &PortError{causedBy: err}
+	}
+
+	return nil
 }
 
 func createOverlappedEvent() (*syscall.Overlapped, error) {

syscall_windows.go

@@ -25,3 +25,7 @@ package serial
 //sys getOverlappedResult(handle syscall.Handle, overlapEvent *syscall.Overlapped, n *uint32, wait bool) (err error) = GetOverlappedResult
 
 //sys purgeComm(handle syscall.Handle, flags uint32) (err error) = PurgeComm
+
+//sys setCommBreak(handle syscall.Handle) (err error) = SetCommBreak
+
+//sys clearCommBreak(handle syscall.Handle) (err error) = ClearCommBreak

zsyscall_windows.go

@@ -42,6 +42,7 @@ var (
 	modkernel32 = windows.NewLazySystemDLL("kernel32.dll")
 
 	procRegEnumValueW       = modadvapi32.NewProc("RegEnumValueW")
+	procClearCommBreak      = modkernel32.NewProc("ClearCommBreak")
 	procCreateEventW        = modkernel32.NewProc("CreateEventW")
 	procEscapeCommFunction  = modkernel32.NewProc("EscapeCommFunction")
 	procGetCommModemStatus  = modkernel32.NewProc("GetCommModemStatus")
@@ -49,6 +50,7 @@ var (
 	procGetOverlappedResult = modkernel32.NewProc("GetOverlappedResult")
 	procPurgeComm           = modkernel32.NewProc("PurgeComm")
 	procResetEvent          = modkernel32.NewProc("ResetEvent")
+	procSetCommBreak        = modkernel32.NewProc("SetCommBreak")
 	procSetCommState        = modkernel32.NewProc("SetCommState")
 	procSetCommTimeouts     = modkernel32.NewProc("SetCommTimeouts")
 )
@@ -61,6 +63,14 @@ func regEnumValue(key syscall.Handle, index uint32, name *uint16, nameLen *uint3
 	return
 }
 
+func clearCommBreak(handle syscall.Handle) (err error) {
+	r1, _, e1 := syscall.Syscall(procClearCommBreak.Addr(), 1, uintptr(handle), 0, 0)
+	if r1 == 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
+
 func createEvent(eventAttributes *uint32, manualReset bool, initialState bool, name *uint16) (handle syscall.Handle, err error) {
 	var _p0 uint32
 	if manualReset {
@@ -126,6 +136,14 @@ func resetEvent(handle syscall.Handle) (err error) {
 	return
 }
 
+func setCommBreak(handle syscall.Handle) (err error) {
+	r1, _, e1 := syscall.Syscall(procSetCommBreak.Addr(), 1, uintptr(handle), 0, 0)
+	if r1 == 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
+
 func setCommState(handle syscall.Handle, dcb *dcb) (err error) {
 	r1, _, e1 := syscall.Syscall(procSetCommState.Addr(), 2, uintptr(handle), uintptr(unsafe.Pointer(dcb)), 0)
 	if r1 == 0 {