Merge pull request #140 from cmaglie/initial_rts_dtr

Allow setting RTS and DTR on `Open`

serial.go

@@ -53,7 +53,7 @@ type Port interface {
 // NoTimeout should be used as a parameter to SetReadTimeout to disable timeout.
 var NoTimeout time.Duration = -1
 
-// ModemStatusBits contains all the modem status bits for a serial port (CTS, DSR, etc...).
+// ModemStatusBits contains all the modem input status bits for a serial port (CTS, DSR, etc...).
 // It can be retrieved with the Port.GetModemStatusBits() method.
 type ModemStatusBits struct {
 	CTS bool // ClearToSend status
@@ -62,6 +62,16 @@ type ModemStatusBits struct {
 	DCD bool // DataCarrierDetect status
 }
 
+// ModemOutputBits contains all the modem output bits for a serial port.
+// This is used in the Mode.InitialStatusBits struct to specify the initial status of the bits.
+// Note: Linux and MacOSX (and basically all unix-based systems) can not set the status bits
+// before opening the port, even if the initial state of the bit is set to false they will go
+// anyway to true for a few milliseconds, resulting in a small pulse.
+type ModemOutputBits struct {
+	RTS bool // ReadyToSend status
+	DTR bool // DataTerminalReady status
+}
+
 // Open opens the serial port using the specified modes
 func Open(portName string, mode *Mode) (Port, error) {
 	return nativeOpen(portName, mode)
@@ -78,6 +88,7 @@ type Mode struct {
 	DataBits          int              // Size of the character (must be 5, 6, 7 or 8)
 	Parity            Parity           // Parity (see Parity type for more info)
 	StopBits          StopBits         // Stop bits (see StopBits type for more info)
+	InitialStatusBits *ModemOutputBits // Initial output modem bits status (if nil defaults to DTR=true and RTS=true)
 }
 
 // Parity describes a serial port parity setting

serial_unix.go

@@ -240,6 +240,26 @@ func nativeOpen(portName string, mode *Mode) (*unixPort, error) {
 		return nil, &PortError{code: InvalidSerialPort}
 	}
 
+	if mode.InitialStatusBits != nil {
+		status, err := port.getModemBitsStatus()
+		if err != nil {
+			return nil, &PortError{code: InvalidSerialPort, causedBy: err}
+		}
+		if mode.InitialStatusBits.DTR {
+			status |= unix.TIOCM_DTR
+		} else {
+			status &^= unix.TIOCM_DTR
+		}
+		if mode.InitialStatusBits.RTS {
+			status |= unix.TIOCM_RTS
+		} else {
+			status &^= unix.TIOCM_RTS
+		}
+		if err := port.setModemBitsStatus(status); err != nil {
+			return nil, &PortError{code: InvalidSerialPort, causedBy: err}
+		}
+	}
+
 	// MacOSX require that this operation is the last one otherwise an
 	// 'Invalid serial port' error is returned... don't know why...
 	if port.SetMode(mode) != nil {

serial_windows.go

@@ -450,10 +450,19 @@ func nativeOpen(portName string, mode *Mode) (*windowsPort, error) {
 		port.Close()
 		return nil, &PortError{code: InvalidSerialPort}
 	}
-	params.Flags &= dcbRTSControlDisbaleMask
-	params.Flags |= dcbRTSControlEnable
 	params.Flags &= dcbDTRControlDisableMask
+	params.Flags &= dcbRTSControlDisbaleMask
+	if mode.InitialStatusBits == nil {
 		params.Flags |= dcbDTRControlEnable
+		params.Flags |= dcbRTSControlEnable
+	} else {
+		if mode.InitialStatusBits.DTR {
+			params.Flags |= dcbDTRControlEnable
+		}
+		if mode.InitialStatusBits.RTS {
+			params.Flags |= dcbRTSControlEnable
+		}
+	}
 	params.Flags &^= dcbOutXCTSFlow
 	params.Flags &^= dcbOutXDSRFlow
 	params.Flags &^= dcbDSRSensitivity