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serial_windows.go
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serial_windows.go
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//
// Copyright 2014-2024 Cristian Maglie. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//
package serial
/*
// MSDN article on Serial Communications:
// http://msdn.microsoft.com/en-us/library/ff802693.aspx
// (alternative link) https://msdn.microsoft.com/en-us/library/ms810467.aspx
// Arduino Playground article on serial communication with Windows API:
// http://playground.arduino.cc/Interfacing/CPPWindows
*/
import (
"errors"
"sync"
"syscall"
"time"
"golang.org/x/sys/windows"
"golang.org/x/sys/windows/registry"
)
type windowsPort struct {
mu sync.Mutex
handle windows.Handle
}
func nativeGetPortsList() ([]string, error) {
key, err := registry.OpenKey(windows.HKEY_LOCAL_MACHINE, `HARDWARE\DEVICEMAP\SERIALCOMM\`, windows.KEY_READ)
switch {
case errors.Is(err, syscall.ERROR_FILE_NOT_FOUND):
// On machines with no serial ports the registry key does not exist.
// Return this as no serial ports instead of an error.
return nil, nil
case err != nil:
return nil, &PortError{code: ErrorEnumeratingPorts, causedBy: err}
}
defer key.Close()
list, err := key.ReadValueNames(0)
if err != nil {
return nil, &PortError{code: ErrorEnumeratingPorts, causedBy: err}
}
return list, nil
}
func (port *windowsPort) Close() error {
port.mu.Lock()
defer func() {
port.handle = 0
port.mu.Unlock()
}()
if port.handle == 0 {
return nil
}
return windows.CloseHandle(port.handle)
}
func (port *windowsPort) Read(p []byte) (int, error) {
var readed uint32
ev, err := createOverlappedEvent()
if err != nil {
return 0, err
}
defer windows.CloseHandle(ev.HEvent)
err = windows.ReadFile(port.handle, p, &readed, ev)
if err == windows.ERROR_IO_PENDING {
err = windows.GetOverlappedResult(port.handle, ev, &readed, true)
}
switch err {
case nil:
// operation completed successfully
case windows.ERROR_OPERATION_ABORTED:
// port may have been closed
return int(readed), &PortError{code: PortClosed, causedBy: err}
default:
// error happened
return int(readed), err
}
if readed > 0 {
return int(readed), nil
}
// Timeout
return 0, nil
}
func (port *windowsPort) Write(p []byte) (int, error) {
var writed uint32
ev, err := createOverlappedEvent()
if err != nil {
return 0, err
}
defer windows.CloseHandle(ev.HEvent)
err = windows.WriteFile(port.handle, p, &writed, ev)
if err == windows.ERROR_IO_PENDING {
// wait for write to complete
err = windows.GetOverlappedResult(port.handle, ev, &writed, true)
}
return int(writed), err
}
func (port *windowsPort) Drain() (err error) {
return windows.FlushFileBuffers(port.handle)
}
func (port *windowsPort) ResetInputBuffer() error {
return windows.PurgeComm(port.handle, windows.PURGE_RXCLEAR|windows.PURGE_RXABORT)
}
func (port *windowsPort) ResetOutputBuffer() error {
return windows.PurgeComm(port.handle, windows.PURGE_TXCLEAR|windows.PURGE_TXABORT)
}
const (
dcbBinary uint32 = 0x00000001
dcbParity = 0x00000002
dcbOutXCTSFlow = 0x00000004
dcbOutXDSRFlow = 0x00000008
dcbDTRControlDisableMask = ^uint32(0x00000030)
dcbDTRControlEnable = 0x00000010
dcbDTRControlHandshake = 0x00000020
dcbDSRSensitivity = 0x00000040
dcbTXContinueOnXOFF = 0x00000080
dcbOutX = 0x00000100
dcbInX = 0x00000200
dcbErrorChar = 0x00000400
dcbNull = 0x00000800
dcbRTSControlDisableMask = ^uint32(0x00003000)
dcbRTSControlEnable = 0x00001000
dcbRTSControlHandshake = 0x00002000
dcbRTSControlToggle = 0x00003000
dcbAbortOnError = 0x00004000
)
var parityMap = map[Parity]byte{
NoParity: windows.NOPARITY,
OddParity: windows.ODDPARITY,
EvenParity: windows.EVENPARITY,
MarkParity: windows.MARKPARITY,
SpaceParity: windows.SPACEPARITY,
}
var stopBitsMap = map[StopBits]byte{
OneStopBit: windows.ONESTOPBIT,
OnePointFiveStopBits: windows.ONE5STOPBITS,
TwoStopBits: windows.TWOSTOPBITS,
}
func (port *windowsPort) SetMode(mode *Mode) error {
params := windows.DCB{}
if windows.GetCommState(port.handle, ¶ms) != nil {
port.Close()
return &PortError{code: InvalidSerialPort}
}
port.setModeParams(mode, ¶ms)
if windows.SetCommState(port.handle, ¶ms) != nil {
port.Close()
return &PortError{code: InvalidSerialPort}
}
return nil
}
func (port *windowsPort) setModeParams(mode *Mode, params *windows.DCB) {
if mode.BaudRate == 0 {
params.BaudRate = windows.CBR_9600 // Default to 9600
} else {
params.BaudRate = uint32(mode.BaudRate)
}
if mode.DataBits == 0 {
params.ByteSize = 8 // Default to 8 bits
} else {
params.ByteSize = byte(mode.DataBits)
}
params.StopBits = stopBitsMap[mode.StopBits]
params.Parity = parityMap[mode.Parity]
}
func (port *windowsPort) SetDTR(dtr bool) error {
// Like for RTS there are problems with the windows.EscapeCommFunction
// observed behaviour was that DTR is set from false -> true
// when setting RTS from true -> false
// 1) Connect -> RTS = true (low) DTR = true (low) OKAY
// 2) SetDTR(false) -> RTS = true (low) DTR = false (high) OKAY
// 3) SetRTS(false) -> RTS = false (high) DTR = true (low) ERROR: DTR toggled
//
// In addition this way the CommState Flags are not updated
/*
var err error
if dtr {
err = windows.EscapeCommFunction(port.handle, windows.SETDTR)
} else {
err = windows.EscapeCommFunction(port.handle, windows.CLTDTR)
}
if err != nil {
return &PortError{}
}
return nil
*/
// The following seems a more reliable way to do it
params := &windows.DCB{}
if err := windows.GetCommState(port.handle, params); err != nil {
return &PortError{causedBy: err}
}
params.Flags &= dcbDTRControlDisableMask
if dtr {
params.Flags |= windows.DTR_CONTROL_ENABLE
}
if err := windows.SetCommState(port.handle, params); err != nil {
return &PortError{causedBy: err}
}
return nil
}
func (port *windowsPort) SetRTS(rts bool) error {
// It seems that there is a bug in the Windows VCP driver:
// it doesn't send USB control message when the RTS bit is
// changed, so the following code not always works with
// USB-to-serial adapters.
//
// In addition this way the CommState Flags are not updated
/*
var err error
if rts {
err = windows.EscapeCommFunction(port.handle, windows.SETRTS)
} else {
err = windows.EscapeCommFunction(port.handle, windows.CLRRTS)
}
if err != nil {
return &PortError{}
}
return nil
*/
// The following seems a more reliable way to do it
params := &windows.DCB{}
if err := windows.GetCommState(port.handle, params); err != nil {
return &PortError{causedBy: err}
}
params.Flags &= dcbRTSControlDisableMask
if rts {
params.Flags |= windows.RTS_CONTROL_ENABLE
}
if err := windows.SetCommState(port.handle, params); err != nil {
return &PortError{causedBy: err}
}
return nil
}
func (port *windowsPort) GetModemStatusBits() (*ModemStatusBits, error) {
var bits uint32
if err := windows.GetCommModemStatus(port.handle, &bits); err != nil {
return nil, &PortError{}
}
return &ModemStatusBits{
CTS: (bits & windows.EV_CTS) != 0,
DCD: (bits & windows.EV_RLSD) != 0,
DSR: (bits & windows.EV_DSR) != 0,
RI: (bits & windows.EV_RING) != 0,
}, nil
}
func (port *windowsPort) SetReadTimeout(timeout time.Duration) error {
commTimeouts := &windows.CommTimeouts{
ReadIntervalTimeout: 0xFFFFFFFF,
ReadTotalTimeoutMultiplier: 0xFFFFFFFF,
ReadTotalTimeoutConstant: 0xFFFFFFFE,
WriteTotalTimeoutConstant: 0,
WriteTotalTimeoutMultiplier: 0,
}
if timeout != NoTimeout {
ms := timeout.Milliseconds()
if ms > 0xFFFFFFFE || ms < 0 {
return &PortError{code: InvalidTimeoutValue}
}
commTimeouts.ReadTotalTimeoutConstant = uint32(ms)
}
if err := windows.SetCommTimeouts(port.handle, commTimeouts); err != nil {
return &PortError{code: InvalidTimeoutValue, causedBy: err}
}
return nil
}
func (port *windowsPort) Break(d time.Duration) error {
if err := windows.SetCommBreak(port.handle); err != nil {
return &PortError{causedBy: err}
}
time.Sleep(d)
if err := windows.ClearCommBreak(port.handle); err != nil {
return &PortError{causedBy: err}
}
return nil
}
func createOverlappedEvent() (*windows.Overlapped, error) {
h, err := windows.CreateEvent(nil, 1, 0, nil)
return &windows.Overlapped{HEvent: h}, err
}
func nativeOpen(portName string, mode *Mode) (*windowsPort, error) {
portName = "\\\\.\\" + portName
path, err := windows.UTF16PtrFromString(portName)
if err != nil {
return nil, err
}
handle, err := windows.CreateFile(
path,
windows.GENERIC_READ|windows.GENERIC_WRITE,
0, nil,
windows.OPEN_EXISTING,
windows.FILE_FLAG_OVERLAPPED,
0)
if err != nil {
switch err {
case windows.ERROR_ACCESS_DENIED:
return nil, &PortError{code: PortBusy}
case windows.ERROR_FILE_NOT_FOUND:
return nil, &PortError{code: PortNotFound}
}
return nil, err
}
// Create the serial port
port := &windowsPort{
handle: handle,
}
// Set port parameters
params := &windows.DCB{}
if windows.GetCommState(port.handle, params) != nil {
port.Close()
return nil, &PortError{code: InvalidSerialPort}
}
port.setModeParams(mode, params)
params.Flags &= dcbDTRControlDisableMask
params.Flags &= dcbRTSControlDisableMask
if mode.InitialStatusBits == nil {
params.Flags |= windows.DTR_CONTROL_ENABLE
params.Flags |= windows.RTS_CONTROL_ENABLE
} else {
if mode.InitialStatusBits.DTR {
params.Flags |= windows.DTR_CONTROL_ENABLE
}
if mode.InitialStatusBits.RTS {
params.Flags |= windows.RTS_CONTROL_ENABLE
}
}
params.Flags &^= dcbOutXCTSFlow
params.Flags &^= dcbOutXDSRFlow
params.Flags &^= dcbDSRSensitivity
params.Flags |= dcbTXContinueOnXOFF
params.Flags &^= dcbInX
params.Flags &^= dcbOutX
params.Flags &^= dcbErrorChar
params.Flags &^= dcbNull
params.Flags &^= dcbAbortOnError
params.XonLim = 2048
params.XoffLim = 512
params.XonChar = 17 // DC1
params.XoffChar = 19 // C3
if windows.SetCommState(port.handle, params) != nil {
port.Close()
return nil, &PortError{code: InvalidSerialPort}
}
if port.SetReadTimeout(NoTimeout) != nil {
port.Close()
return nil, &PortError{code: InvalidSerialPort}
}
return port, nil
}