Allow setting custom baudrates on serial ports (mac and linux version)

Co-authored-by: Jan-Philipp Benecke <github@bnck.me>

serial_darwin.go

@@ -14,3 +14,18 @@ const regexFilter = "^(cu|tty)\\..*"
 const ioctlTcgetattr = unix.TIOCGETA
 const ioctlTcsetattr = unix.TIOCSETA
 const ioctlTcflsh = unix.TIOCFLUSH
+
+func setTermSettingsBaudrate(speed int, settings *unix.Termios) (error, bool) {
+	baudrate, ok := baudrateMap[speed]
+	if !ok {
+		return nil, true
+	}
+	settings.Ispeed = toTermiosSpeedType(baudrate)
+	settings.Ospeed = toTermiosSpeedType(baudrate)
+	return nil, false
+}
+
+func (port *unixPort) setSpecialBaudrate(speed uint32) error {
+	const kIOSSIOSPEED = 0x80045402
+	return unix.IoctlSetPointerInt(port.handle, kIOSSIOSPEED, int(speed))
+}

serial_linux.go

@@ -67,3 +67,31 @@ const ioctlTcflsh = unix.TCFLSH
 func toTermiosSpeedType(speed uint32) uint32 {
 	return speed
 }
+
+func setTermSettingsBaudrate(speed int, settings *unix.Termios) (error, bool) {
+	baudrate, ok := baudrateMap[speed]
+	if !ok {
+		return nil, true
+	}
+	// revert old baudrate
+	for _, rate := range baudrateMap {
+		settings.Cflag &^= rate
+	}
+	// set new baudrate
+	settings.Cflag |= baudrate
+	settings.Ispeed = toTermiosSpeedType(baudrate)
+	settings.Ospeed = toTermiosSpeedType(baudrate)
+	return nil, false
+}
+
+func (port *unixPort) setSpecialBaudrate(speed uint32) error {
+	settings, err := unix.IoctlGetTermios(port.handle, unix.TCGETS2)
+	if err != nil {
+		return err
+	}
+	settings.Cflag &^= unix.CBAUD
+	settings.Cflag |= unix.BOTHER
+	settings.Ispeed = speed
+	settings.Ospeed = speed
+	return unix.IoctlSetTermios(port.handle, unix.TCSETS2, settings)
+}

serial_unix.go

@@ -126,9 +126,6 @@ func (port *unixPort) SetMode(mode *Mode) error {
 	if err != nil {
 		return err
 	}
-	if err := setTermSettingsBaudrate(mode.BaudRate, settings); err != nil {
-		return err
-	}
 	if err := setTermSettingsParity(mode.Parity, settings); err != nil {
 		return err
 	}
@@ -138,7 +135,21 @@ func (port *unixPort) SetMode(mode *Mode) error {
 	if err := setTermSettingsStopBits(mode.StopBits, settings); err != nil {
 		return err
 	}
-	return port.setTermSettings(settings)
+	requireSpecialBaudrate := false
+	if err, special := setTermSettingsBaudrate(mode.BaudRate, settings); err != nil {
+		return err
+	} else if special {
+		requireSpecialBaudrate = true
+	}
+	if err := port.setTermSettings(settings); err != nil {
+		return err
+	}
+	if requireSpecialBaudrate {
+		if err := port.setSpecialBaudrate(uint32(mode.BaudRate)); err != nil {
+			return err
+		}
+	}
+	return nil
 }
 
 func (port *unixPort) SetDTR(dtr bool) error {
@@ -289,22 +300,6 @@ func nativeGetPortsList() ([]string, error) {
 
 // termios manipulation functions
 
-func setTermSettingsBaudrate(speed int, settings *unix.Termios) error {
-	baudrate, ok := baudrateMap[speed]
-	if !ok {
-		return &PortError{code: InvalidSpeed}
-	}
-	// revert old baudrate
-	for _, rate := range baudrateMap {
-		settings.Cflag &^= rate
-	}
-	// set new baudrate
-	settings.Cflag |= baudrate
-	settings.Ispeed = toTermiosSpeedType(baudrate)
-	settings.Ospeed = toTermiosSpeedType(baudrate)
-	return nil
-}
-
 func setTermSettingsParity(parity Parity, settings *unix.Termios) error {
 	switch parity {
 	case NoParity: