// Open a connection with a read timeout.
func (connection *Connection) Open(timeout uint8) error {
var err error
// The serial port is basically a file we are writing to and reading from.
// O_RDWR allows the program to read and write the file.
// O_NOCTTY prevents the device from controlling the terminal.
// O_NONBLOCK prevents the system from blocking for a long time.
connection.f, err = os.OpenFile(connection.Port,
syscall.O_RDWR|syscall.O_NOCTTY|syscall.O_NONBLOCK, 0666)
if err != nil {
return err
}
// Close the file on error occurrence.
defer func() {
if err != nil && connection.f != nil {
connection.f.Close()
}
}()
// Create a plain termios, which allows the program to execute
// input/output operations.
termios := syscall.Termios{}
// Setup the baud rate in the termios structure.
baudrate := baudrates[connection.Baud]
termios.Cflag |= baudrate
termios.Ispeed = baudrate
termios.Ospeed = baudrate
// Setup stop bits in the termios structure.
switch connection.StopBit {
case StopBit1:
termios.Cflag &^= syscall.CSTOPB // CSTOPB = 0x40
case StopBit2:
termios.Cflag |= syscall.CSTOPB
default:
return errStopBit
}
// Setup data bits in the termios structure.
databit := databits[connection.DataBit]
termios.Cflag |= databit
// Setup parity in the termios structure.
switch connection.Parity {
case ParityNone:
termios.Cflag &^= syscall.PARENB // PARENB = 0x100
case ParityEven:
termios.Cflag |= syscall.PARENB
case ParityOdd:
termios.Cflag |= syscall.PARENB
termios.Cflag |= syscall.PARODD // PARODD = 0x200
default:
return errParity
}
// // set blocking / non-blocking read
vmin := uint8(0)
if timeout == 0 {
vmin = 1
}
// Attach min bytes and timeout to the termios structure.
termios.Cc = [32]uint8{
syscall.VMIN: vmin, // min bytes per transfer
syscall.VTIME: timeout, // actual read timeout in deciseconds
}
// Execute IOCTL with the modified termios structure to apply the changes.
if _, _, errno := syscall.Syscall6(
// device-specific input/output operations
syscall.SYS_IOCTL,
// open file descriptor
uintptr(connection.f.Fd()),
// a request code number to set the current serial port settings
uintptr(syscall.TCSETS),
//TODO: it looks like syscall.TCSETS is not available under
// freebsd and darwin. Is this a bug?
uintptr(unsafe.Pointer(&termios)), // a pointer to the termios structure
0,
0,
0,
); errno != 0 {
return errno
}
connection.isOpen = true
return nil
}
