Improves NonBlocking mode config

- Removed the need for NonBlockingRead boolean
- Setting ReadTimeout to positive value sets non blocking mode
- ReadTimeout is specified in milliseconds irrespective of platform
- Caps ReadTimeout on Linux / POSIX systems
- Updated README

README.md

@@ -60,11 +60,17 @@ func main() {
 
 NonBlocking Mode
 ----------------
+By default goserial reads in blocking mode. Which means Read() will
+block until at least one byte is returned. If that's not what you want,
+specify a ReadTimeout in milliseconds and the Read() will timeout
+returning 0 bytes if no bytes are read.
+
+```go
+	c := &serial.Config{Name: "COM45", Baud: 115200, ReadTimeout: 1000}
 
-```go	
-	c := &serial.Config{Name: "COM45", Baud: 115200, NonBlockingRead: true, ReadTimeout: 1000}
-	// On Windows, ReadTimeout is in milliseconds (1000 = 1sec)
-	// where as on Linux and POSIX systems, ReadTimeout is in deciseconds (10 = 1sec)
+	// In this mode, you will want to suppress error for read
+	// as 0 bytes returns EOF error on Linux / POSIX
+	n, _ = s.Read(buf)
 ```
 
 Possible Future Work

serial.go

@@ -65,12 +65,11 @@ import "io"
 //
 // For example:
 //
-//    c0 := &serial.Config{Name: "COM45", Baud: 115200, NonBlockingRead: true, ReadTimeout: 1000}
+//    c0 := &serial.Config{Name: "COM45", Baud: 115200, ReadTimeout: 1000}
 // or
 //    c1 := new(serial.Config)
 //    c1.Name = "/dev/tty.usbserial"
 //    c1.Baud = 115200
-//    c1.NonBlockingRead = true
 //    c1.ReadTimeout = 1000
 //
 type Config struct {
@@ -86,13 +85,12 @@ type Config struct {
 	// XONFlowControl bool
 
 	// CRLFTranslate bool
-	NonBlockingRead bool
-	ReadTimeout     uint32
+	ReadTimeout uint32
 }
 
 // OpenPort opens a serial port with the specified configuration
 func OpenPort(c *Config) (io.ReadWriteCloser, error) {
-	return openPort(c.Name, c.Baud, c.NonBlockingRead, c.ReadTimeout)
+	return openPort(c.Name, c.Baud, c.ReadTimeout)
 }
 
 // func Flush()

serial_linux.go

@@ -9,7 +9,7 @@ import (
 	"unsafe"
 )
 
-func openPort(name string, baud int, nonBlockingRead bool, readTimeout uint32) (rwc io.ReadWriteCloser, err error) {
+func openPort(name string, baud int, readTimeout uint32) (rwc io.ReadWriteCloser, err error) {
 
 	var bauds = map[int]uint32{
 		50:      syscall.B50,
@@ -64,8 +64,19 @@ func openPort(name string, baud int, nonBlockingRead bool, readTimeout uint32) (
 	fd := f.Fd()
 	// set blocking / non-blocking read
 	var minBytesToRead uint8 = 1
-	if nonBlockingRead == true {
+	if readTimeout > 0 {
+		// EOF on zero read
 		minBytesToRead = 0
+		// capping the timeout
+		if readTimeout < 100 {
+			// min possible timeout
+			readTimeout = 100
+		} else if readTimeout > 25500 {
+			// max possible timeout
+			readTimeout = 25500
+		}
+		// convert milliseconds to deciseconds as expected by VTIME
+		readTimeout = readTimeout / 100
 	}
 	t := syscall.Termios{
 		Iflag:  syscall.IGNPAR,

serial_posix.go

@@ -17,7 +17,7 @@ import (
 	//"unsafe"
 )
 
-func openPort(name string, baud int, nonBlockingRead bool, readTimeout uint32) (rwc io.ReadWriteCloser, err error) {
+func openPort(name string, baud int, readTimeout uint32) (rwc io.ReadWriteCloser, err error) {
 	f, err := os.OpenFile(name, syscall.O_RDWR|syscall.O_NOCTTY|syscall.O_NONBLOCK, 0666)
 	if err != nil {
 		return
@@ -77,19 +77,30 @@ func openPort(name string, baud int, nonBlockingRead bool, readTimeout uint32) (
 	// Select raw mode
 	st.c_lflag &= ^C.tcflag_t(C.ICANON | C.ECHO | C.ECHOE | C.ISIG)
 	st.c_oflag &= ^C.tcflag_t(C.OPOST)
-	
+
 	// set blocking / non-blocking read
-	var minBytesToRead uint8 = 1	
-	if nonBlockingRead == true {
+	/*
+	*	http://man7.org/linux/man-pages/man3/termios.3.html
+	* - Supports blocking read and read with timeout operations
+	 */
+	var minBytesToRead uint8 = 1
+	if readTimeout > 0 {
 		// EOF on zero read
 		minBytesToRead = 0
+		// capping the timeout
+		if readTimeout < 100 {
+			// min possible timeout
+			readTimeout = 100
+		} else if readTimeout > 25500 {
+			// max possible timeout
+			readTimeout = 25500
+		}
+		// convert milliseconds to deciseconds as expected by VTIME
+		readTimeout = readTimeout / 100
 	}
 	st.c_cc[C.VMIN] = C.cc_t(minBytesToRead)
 	st.c_cc[C.VTIME] = C.cc_t(readTimeout)
-
-	st.c_oflag &= ^C.tcflag_t(C.OPOST)
-	st.c_oflag &= ^C.tcflag_t(C.OPOST)
-
+
 	_, err = C.tcsetattr(fd, C.TCSANOW, &st)
 	if err != nil {
 		f.Close()

serial_windows.go

@@ -37,7 +37,7 @@ type structTimeouts struct {
 	WriteTotalTimeoutConstant   uint32
 }
 
-func openPort(name string, baud int, nonBlockingRead bool, readTimeout uint32) (rwc io.ReadWriteCloser, err error) {
+func openPort(name string, baud int, readTimeout uint32) (rwc io.ReadWriteCloser, err error) {
 	if len(name) > 0 && name[0] != '\\' {
 		name = "\\\\.\\" + name
 	}
@@ -65,7 +65,7 @@ func openPort(name string, baud int, nonBlockingRead bool, readTimeout uint32) (
 	if err = setupComm(h, 64, 64); err != nil {
 		return
 	}
-	if err = setCommTimeouts(h, nonBlockingRead, readTimeout); err != nil {
+	if err = setCommTimeouts(h, readTimeout); err != nil {
 		return
 	}
 	if err = setCommMask(h); err != nil {
@@ -178,18 +178,20 @@ func setCommState(h syscall.Handle, baud int) error {
 	return nil
 }
 
-func setCommTimeouts(h syscall.Handle, nonBlockingRead bool, readTimeout uint32) error {
+func setCommTimeouts(h syscall.Handle, readTimeout uint32) error {
 	var timeouts structTimeouts
 	const MAXDWORD = 1<<32 - 1
-	if nonBlockingRead == true {
+	if readTimeout > 0 {
+		// non-blocking read
 		timeouts.ReadIntervalTimeout = 1000
 		timeouts.ReadTotalTimeoutMultiplier = 0
 		timeouts.ReadTotalTimeoutConstant = readTimeout
 	} else {
+		// blocking read
 		timeouts.ReadIntervalTimeout = MAXDWORD
 		timeouts.ReadTotalTimeoutMultiplier = MAXDWORD
 		timeouts.ReadTotalTimeoutConstant = MAXDWORD - 1
-	}	
+	}
 
 	/* From http://msdn.microsoft.com/en-us/library/aa363190(v=VS.85).aspx