serial_linux.go

// +build linux,!cgo

package serial

import (
	"os"
	"syscall"
	"time"
	"unsafe"
)

func openPort(name string, baud int, databits byte, parity Parity, stopbits StopBits, readTimeout time.Duration) (p *Port, err error) {
	var bauds = map[int]uint32{
		50:      syscall.B50,
		75:      syscall.B75,
		110:     syscall.B110,
		134:     syscall.B134,
		150:     syscall.B150,
		200:     syscall.B200,
		300:     syscall.B300,
		600:     syscall.B600,
		1200:    syscall.B1200,
		1800:    syscall.B1800,
		2400:    syscall.B2400,
		4800:    syscall.B4800,
		9600:    syscall.B9600,
		19200:   syscall.B19200,
		38400:   syscall.B38400,
		57600:   syscall.B57600,
		115200:  syscall.B115200,
		230400:  syscall.B230400,
		460800:  syscall.B460800,
		500000:  syscall.B500000,
		576000:  syscall.B576000,
		921600:  syscall.B921600,
		1000000: syscall.B1000000,
		1152000: syscall.B1152000,
		1500000: syscall.B1500000,
		2000000: syscall.B2000000,
		2500000: syscall.B2500000,
		3000000: syscall.B3000000,
		3500000: syscall.B3500000,
		4000000: syscall.B4000000,
	}

	rate := bauds[baud]

	if rate == 0 {
		return
	}

	f, err := os.OpenFile(name, syscall.O_RDWR|syscall.O_NOCTTY|syscall.O_NONBLOCK, 0666)
	if err != nil {
		return nil, err
	}

	defer func() {
		if err != nil && f != nil {
			f.Close()
		}
	}()

	// Base settings
	cflagToUse := syscall.CREAD | syscall.CLOCAL | rate
	switch databits {
	case 5:
		cflagToUse |= syscall.CS5
	case 6:
		cflagToUse |= syscall.CS6
	case 7:
		cflagToUse |= syscall.CS7
	case 8:
		cflagToUse |= syscall.CS8
	default:
		return nil, ErrBadSize
	}
	// Stop bits settings
	switch stopbits {
	case Stop1:
		// default is 1 stop bit
	case Stop2:
		cflagToUse |= syscall.CSTOPB
	default:
		// Don't know how to set 1.5
		return nil, ErrBadStopBits
	}
	// Parity settings
	switch parity {
	case ParityNone:
		// default is no parity
	case ParityOdd:
		cflagToUse |= syscall.PARENB
		cflagToUse |= syscall.PARODD
	case ParityEven:
		cflagToUse |= syscall.PARENB
	default:
		return nil, ErrBadParity
	}
	fd := f.Fd()
	vmin, vtime := posixTimeoutValues(readTimeout)
	t := syscall.Termios{
		Iflag:  syscall.IGNPAR,
		Cflag:  cflagToUse,
		Cc:     [32]uint8{syscall.VMIN: vmin, syscall.VTIME: vtime},
		Ispeed: rate,
		Ospeed: rate,
	}

	if _, _, errno := syscall.Syscall6(
		syscall.SYS_IOCTL,
		uintptr(fd),
		uintptr(syscall.TCSETS),
		uintptr(unsafe.Pointer(&t)),
		0,
		0,
		0,
	); errno != 0 {
		return nil, errno
	}

	if err = syscall.SetNonblock(int(fd), false); err != nil {
		return
	}

	return &Port{f: f}, nil
}

type Port struct {
	// We intentionly do not use an "embedded" struct so that we
	// don't export File
	f *os.File
}

func (p *Port) Read(b []byte) (n int, err error) {
	return p.f.Read(b)
}

func (p *Port) Write(b []byte) (n int, err error) {
	return p.f.Write(b)
}

// Discards data written to the port but not transmitted,
// or data received but not read
func (p *Port) Flush() error {
	const TCFLSH = 0x540B
	_, _, err := syscall.Syscall(
		syscall.SYS_IOCTL,
		uintptr(p.f.Fd()),
		uintptr(TCFLSH),
		uintptr(syscall.TCIOFLUSH),
	)
	return err
}

func (p *Port) Close() (err error) {
	return p.f.Close()
}