How to set baud rate to 307200 on Linux?

Question

Basically I\'m using the following code to set the baud rate of a serial port:

struct termios options;
tcgetattr(fd, &options);
cfsetispeed(&options,         


        

Answer 1

Try the ioctl call - you can specify an arbitrary baud rate. That is,

ioctl(serialFileDescriptor, IOSSIOSPEED, &baudRate);

To open the serial port:

// Open the serial like POSIX C
serialFileDescriptor = open(
    "/dev/tty.usbserial-A6008cD3",
    O_RDWR |
    O_NOCTTY |
    O_NONBLOCK );

// Block non-root users from using this port
ioctl(serialFileDescriptor, TIOCEXCL);

// Clear the O_NONBLOCK flag, so that read() will
//   block and wait for data.
fcntl(serialFileDescriptor, F_SETFL, 0);

// Grab the options for the serial port
tcgetattr(serialFileDescriptor, &options);

// Setting raw-mode allows the use of tcsetattr() and ioctl()
cfmakeraw(&options);

// Specify any arbitrary baud rate
ioctl(serialFileDescriptor, IOSSIOSPEED, &baudRate);

To read from the serial port:

// This selector will be called as another thread
- (void)incomingTextUpdateThread: (NSThread *) parentThread {
    char byte_buffer[100]; // Buffer for holding incoming data
    int numBytes=1; // Number of bytes read during read

    // Create a pool so we can use regular Cocoa stuff.
    //   Child threads can't re-use the parent's autorelease pool
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    // This will loop until the serial port closes
    while(numBytes>0) {
        // read() blocks until data is read or the port is closed
        numBytes = read(serialFileDescriptor, byte_buffer, 100);

        // You would want to do something useful here
        NSLog([NSString stringWithCString:byte_buffer length:numBytes]);
    }
}

To write to the serial port:

uint8_t val = 'A';
write(serialFileDescriptor, val, 1);

To list availble serial ports:

io_object_t serialPort;
io_iterator_t serialPortIterator;

// Ask for all the serial ports
IOServiceGetMatchingServices(
    kIOMasterPortDefault,
    IOServiceMatching(kIOSerialBSDServiceValue),
    &serialPortIterator);

// Loop through all the serial ports
while (serialPort = IOIteratorNext(serialPortIterator)) {
    // You want to do something useful here
    NSLog(
        (NSString*)IORegistryEntryCreateCFProperty(
            serialPort, CFSTR(kIOCalloutDeviceKey),
            kCFAllocatorDefault, 0));
    IOObjectRelease(serialPort);
}

IOObjectRelease(serialPortIterator);