266 lines
6 KiB
Go
266 lines
6 KiB
Go
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// +build darwin linux freebsd openbsd netbsd
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package serial
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import (
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"errors"
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"fmt"
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"log"
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"os"
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"syscall"
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"time"
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"unsafe"
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)
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// port implements Port interface.
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type port struct {
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fd int
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oldTermios *syscall.Termios
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timeout time.Duration
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}
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const (
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rs485Enabled = 1 << 0
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rs485RTSOnSend = 1 << 1
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rs485RTSAfterSend = 1 << 2
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rs485RXDuringTX = 1 << 4
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rs485Tiocs = 0x542f
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)
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// rs485_ioctl_opts is used to configure RS485 options in the driver
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type rs485_ioctl_opts struct {
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flags uint32
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delay_rts_before_send uint32
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delay_rts_after_send uint32
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padding [5]uint32
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}
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// New allocates and returns a new serial port controller.
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func New() Port {
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return &port{fd: -1}
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}
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// Open connects to the given serial port.
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func (p *port) Open(c *Config) (err error) {
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termios, err := newTermios(c)
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if err != nil {
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return
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}
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// See man termios(3).
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// O_NOCTTY: no controlling terminal.
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// O_NDELAY: no data carrier detect.
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p.fd, err = syscall.Open(c.Address, syscall.O_RDWR|syscall.O_NOCTTY|syscall.O_NDELAY|syscall.O_CLOEXEC, 0666)
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if err != nil {
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return
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}
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// Backup current termios to restore on closing.
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p.backupTermios()
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if err = p.setTermios(termios); err != nil {
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// No need to restore termios
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syscall.Close(p.fd)
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p.fd = -1
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p.oldTermios = nil
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return err
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}
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if err = enableRS485(p.fd, &c.RS485); err != nil {
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p.Close()
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return err
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}
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p.timeout = c.Timeout
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return
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}
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func (p *port) Close() (err error) {
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if p.fd == -1 {
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return
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}
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p.restoreTermios()
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err = syscall.Close(p.fd)
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p.fd = -1
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p.oldTermios = nil
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return
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}
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// Read reads from serial port. Port must be opened before calling this method.
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// It is blocked until all data received or timeout after p.timeout.
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func (p *port) Read(b []byte) (n int, err error) {
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var rfds syscall.FdSet
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fd := p.fd
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fdset(fd, &rfds)
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var tv *syscall.Timeval
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if p.timeout > 0 {
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timeout := syscall.NsecToTimeval(p.timeout.Nanoseconds())
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tv = &timeout
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}
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for {
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// If syscall.Select() returns EINTR (Interrupted system call), retry it
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if err = syscallSelect(fd+1, &rfds, nil, nil, tv); err == nil {
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break
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}
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if err != syscall.EINTR {
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err = fmt.Errorf("serial: could not select: %v", err)
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return
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}
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}
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if !fdisset(fd, &rfds) {
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// Timeout
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err = ErrTimeout
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return
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}
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n, err = syscall.Read(fd, b)
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return
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}
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// Write writes data to the serial port.
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func (p *port) Write(b []byte) (n int, err error) {
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n, err = syscall.Write(p.fd, b)
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return
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}
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func (p *port) setTermios(termios *syscall.Termios) (err error) {
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if err = tcsetattr(p.fd, termios); err != nil {
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err = fmt.Errorf("serial: could not set setting: %v", err)
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}
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return
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}
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// backupTermios saves current termios setting.
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// Make sure that device file has been opened before calling this function.
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func (p *port) backupTermios() {
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oldTermios := &syscall.Termios{}
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if err := tcgetattr(p.fd, oldTermios); err != nil {
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// Warning only.
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log.Printf("serial: could not get setting: %v\n", err)
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return
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}
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// Will be reloaded when closing.
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p.oldTermios = oldTermios
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}
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// restoreTermios restores backed up termios setting.
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// Make sure that device file has been opened before calling this function.
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func (p *port) restoreTermios() {
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if p.oldTermios == nil {
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return
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}
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if err := tcsetattr(p.fd, p.oldTermios); err != nil {
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// Warning only.
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log.Printf("serial: could not restore setting: %v\n", err)
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return
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}
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p.oldTermios = nil
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}
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// Helpers for termios
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func newTermios(c *Config) (termios *syscall.Termios, err error) {
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termios = &syscall.Termios{}
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flag := termios.Cflag
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// Baud rate
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if c.BaudRate == 0 {
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// 19200 is the required default.
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flag = syscall.B19200
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} else {
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var ok bool
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flag, ok = baudRates[c.BaudRate]
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if !ok {
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err = fmt.Errorf("serial: unsupported baud rate %v", c.BaudRate)
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return
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}
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}
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termios.Cflag |= flag
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// Input baud.
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cfSetIspeed(termios, flag)
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// Output baud.
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cfSetOspeed(termios, flag)
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// Character size.
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if c.DataBits == 0 {
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flag = syscall.CS8
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} else {
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var ok bool
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flag, ok = charSizes[c.DataBits]
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if !ok {
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err = fmt.Errorf("serial: unsupported character size %v", c.DataBits)
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return
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}
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}
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termios.Cflag |= flag
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// Stop bits
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switch c.StopBits {
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case 0, 1:
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// Default is one stop bit.
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// noop
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case 2:
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// CSTOPB: Set two stop bits.
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termios.Cflag |= syscall.CSTOPB
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default:
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err = fmt.Errorf("serial: unsupported stop bits %v", c.StopBits)
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return
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}
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switch c.Parity {
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case "N":
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// noop
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case "O":
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// PARODD: Parity is odd.
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termios.Cflag |= syscall.PARODD
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fallthrough
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case "", "E":
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// As mentioned in the modbus spec, the default parity mode must be Even parity
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// PARENB: Enable parity generation on output.
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termios.Cflag |= syscall.PARENB
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// INPCK: Enable input parity checking.
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termios.Iflag |= syscall.INPCK
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default:
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err = fmt.Errorf("serial: unsupported parity %v", c.Parity)
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return
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}
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// Control modes.
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// CREAD: Enable receiver.
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// CLOCAL: Ignore control lines.
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termios.Cflag |= syscall.CREAD | syscall.CLOCAL
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// Special characters.
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// VMIN: Minimum number of characters for noncanonical read.
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// VTIME: Time in deciseconds for noncanonical read.
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// Both are unused as NDELAY is we utilized when opening device.
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return
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}
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// enableRS485 enables RS485 functionality of driver via an ioctl if the config says so
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func enableRS485(fd int, config *RS485Config) error {
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if !config.Enabled {
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return nil
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}
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rs485 := rs485_ioctl_opts{
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rs485Enabled,
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uint32(config.DelayRtsBeforeSend / time.Millisecond),
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uint32(config.DelayRtsAfterSend / time.Millisecond),
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[5]uint32{0, 0, 0, 0, 0},
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}
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if config.RtsHighDuringSend {
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rs485.flags |= rs485RTSOnSend
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}
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if config.RtsHighAfterSend {
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rs485.flags |= rs485RTSAfterSend
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}
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if config.RxDuringTx {
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rs485.flags |= rs485RXDuringTX
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}
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r, _, errno := syscall.Syscall(
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syscall.SYS_IOCTL,
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uintptr(fd),
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uintptr(rs485Tiocs),
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uintptr(unsafe.Pointer(&rs485)))
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if errno != 0 {
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return os.NewSyscallError("SYS_IOCTL (RS485)", errno)
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}
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if r != 0 {
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return errors.New("serial: unknown error from SYS_IOCTL (RS485)")
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}
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return nil
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}
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