x/sys/windows: add serial comm functions

Serial ports are still widely used to communicate with a large range of
devices.

This change adds the remaining functions described in "Serial
Communications in Win32", enabling Go applications and libraries to be
written that support the full set of serial port functionality on
Windows.

x/sys/unix already has equivalent functionality through termios.

See https://learn.microsoft.com/en-us/previous-versions/ms810467(v=msdn.10).

windows/syscall_windows.go

@@ -349,8 +349,17 @@ func NewCallbackCDecl(fn interface{}) uintptr {
 //sys	SetProcessPriorityBoost(process Handle, disable bool) (err error) = kernel32.SetProcessPriorityBoost
 //sys	GetProcessWorkingSetSizeEx(hProcess Handle, lpMinimumWorkingSetSize *uintptr, lpMaximumWorkingSetSize *uintptr, flags *uint32)
 //sys	SetProcessWorkingSetSizeEx(hProcess Handle, dwMinimumWorkingSetSize uintptr, dwMaximumWorkingSetSize uintptr, flags uint32) (err error)
+//sys	ClearCommError(handle Handle, lpErrors *uint32, lpStat *ComStat) (err error)
+//sys	EscapeCommFunction(handle Handle, dwFunc uint32) (err error)
+//sys	GetCommState(handle Handle, lpDCB *DCB) (err error)
+//sys	GetCommModemStatus(handle Handle, lpModemStat *uint32) (err error)
 //sys	GetCommTimeouts(handle Handle, timeouts *CommTimeouts) (err error)
+//sys	PurgeComm(handle Handle, dwFlags uint32) (err error)
+//sys	SetCommMask(handle Handle, dwEvtMask uint32) (err error)
+//sys	SetCommState(handle Handle, lpDCB *DCB) (err error)
 //sys	SetCommTimeouts(handle Handle, timeouts *CommTimeouts) (err error)
+//sys	SetupComm(handle Handle, dwInQueue uint32, dwOutQueue uint32) (err error)
+//sys	WaitCommEvent(handle Handle, lpEvtMask *uint32, lpOverlapped *Overlapped) (err error)
 //sys	GetActiveProcessorCount(groupNumber uint16) (ret uint32)
 //sys	GetMaximumProcessorCount(groupNumber uint16) (ret uint32)
 //sys	EnumWindows(enumFunc uintptr, param unsafe.Pointer) (err error) = user32.EnumWindows
@@ -1835,3 +1844,73 @@ func ResizePseudoConsole(pconsole Handle, size Coord) error {
 	// accept arguments that can be casted to uintptr, and Coord can't.
 	return resizePseudoConsole(pconsole, *((*uint32)(unsafe.Pointer(&size))))
 }
+
+// DCB constants. See https://learn.microsoft.com/en-us/windows/win32/api/winbase/ns-winbase-dcb.
+const (
+	CBR_110    = 110
+	CBR_300    = 300
+	CBR_600    = 600
+	CBR_1200   = 1200
+	CBR_2400   = 2400
+	CBR_4800   = 4800
+	CBR_9600   = 9600
+	CBR_14400  = 14400
+	CBR_19200  = 19200
+	CBR_38400  = 38400
+	CBR_57600  = 57600
+	CBR_115200 = 115200
+	CBR_128000 = 128000
+	CBR_256000 = 256000
+
+	DTR_CONTROL_DISABLE   = 0x00
+	DTR_CONTROL_ENABLE    = 0x01
+	DTR_CONTROL_HANDSHAKE = 0x02
+
+	RTS_CONTROL_DISABLE   = 0x00
+	RTS_CONTROL_ENABLE    = 0x01
+	RTS_CONTROL_HANDSHAKE = 0x02
+	RTS_CONTROL_TOGGLE    = 0x03
+
+	NOPARITY    = 0
+	ODDPARITY   = 1
+	EVENPARITY  = 2
+	MARKPARITY  = 3
+	SPACEPARITY = 4
+
+	ONESTOPBIT   = 0
+	ONE5STOPBITS = 1
+	TWOSTOPBITS  = 2
+)
+
+// EscapeCommFunction constants. See https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-escapecommfunction.
+const (
+	SETXOFF  = 1
+	SETXON   = 2
+	SETRTS   = 3
+	CLRRTS   = 4
+	SETDTR   = 5
+	CLRDTR   = 6
+	SETBREAK = 8
+	CLRBREAK = 9
+)
+
+// PurgeComm constants. See https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-purgecomm.
+const (
+	PURGE_TXABORT = 0x0001
+	PURGE_RXABORT = 0x0002
+	PURGE_TXCLEAR = 0x0004
+	PURGE_RXCLEAR = 0x0008
+)
+
+// SetCommMask constants. See https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-setcommmask.
+const (
+	EV_RXCHAR  = 0x0001
+	EV_RXFLAG  = 0x0002
+	EV_TXEMPTY = 0x0004
+	EV_CTS     = 0x0008
+	EV_DSR     = 0x0010
+	EV_RLSD    = 0x0020
+	EV_BREAK   = 0x0040
+	EV_ERR     = 0x0080
+	EV_RING    = 0x0100
+)

windows/types_windows.go

@@ -3380,3 +3380,27 @@ type BLOB struct {
 	Size     uint32
 	BlobData *byte
 }
+
+type ComStat struct {
+	Flags    [4]uint8
+	CBInQue  uint32
+	CBOutQue uint32
+}
+
+type DCB struct {
+	DCBlength  uint32
+	BaudRate   uint32
+	Flags      [4]uint8
+	wReserved  uint16
+	XonLim     uint16
+	XoffLim    uint16
+	ByteSize   uint8
+	Parity     uint8
+	StopBits   uint8
+	XonChar    byte
+	XoffChar   byte
+	ErrorChar  byte
+	EofChar    byte
+	EvtChar    byte
+	wReserved1 uint16
+}