C语言的数据链路层编程

Question

I'm totally newbie about this thing and I want to know where to start..
I have a manual that specifies data link layer that includes command and response frames to access a device connected in /dev/ttyUSB0 .

Example of the given command frame is setting the baud rate

Head = 0x0A
Address = NULL/blank
Length = 0x03
Command = 0x20
Parameter = 0x00
Check = cc

Where parameter 0x00 is equal to baud rate 9600bps.

My question is how do I use this in programming? can I use it on C language?
My OS platform is ubuntu 12.04.
Any link or idea would be a great help.

UPDATE This is the command I used in read()

    unsigned char rx_buffer[1024];
    size_t RX_buffer_len;
    ssize_t bytes_read;
    int fd;

    RX_buffer_len = sizeof(rx_buffer);
    bytes_read = read (serial, rx_buffer, RX_buffer_len);

Answer 1

You could start defining the your packet message structure

// Enable 1 byte alignment
#pragma pack(1)

typedef struct
{
    uint8_t Head;
    uint8_t Address;
    uint8_t Length;
    uint8_t Command;
    uint8_t Parameter;
    uint8_t Check;
}typ_packet;

// Restore the original alignment
#pragma pack()

Then you can access and configure ttyUSB0. A simple example:

struct termios2 t;

int serial, baud;

// Open the uart low level device driver and set up all params
serial_fd = open("/dev/ttyUSB0", O_NOCTTY | O_NDELAY);

if (serial != -1)
{
    baud = 9600;

    if (ioctl(serial, TCGETS2, &t))
    {
        // Fails to read tty pars
        exit(1);
    }

    t.c_cflag &= ~CBAUD;
    t.c_cflag |= BOTHER;
    t.c_cflag |= CSTOPB;
    t.c_ospeed = baud;

    // Noncanonical mode, disable signals, extended
    // input processing, and echoing
    t.c_lflag &= ~(ICANON | ISIG | IEXTEN | ECHO);

    // Disable special handling of CR, NL, and BREAK.
    // No 8th-bit stripping or parity error handling.
    // Disable START/STOP output flow control.
    t.c_iflag &= ~(BRKINT | ICRNL | IGNBRK | IGNCR | INLCR |
                      INPCK | ISTRIP | IXON | PARMRK);

    // Disable all output processing
    t.c_oflag &= ~OPOST;

    if (ioctl(serial, TCSETS2, &t))
    {
        // Failed to set serial parameters
        exit(1);
    }
}
else
{
    // Failed to open ttyUSB0
    exit(1);
}

Then you can simply read from serial line by

res = read (serial_fd, rx_buffer, RX_buffer_len);

And write using

typ_packet packet;

packet.Head = 0x0A;
packet.Address = 0x00;
packet.Length = 0x03;
packet.Command = 0x20;
packet.Parameter = 0x00;
packet.Check = 0xCC;

write(serial_fd, &packet, 6);