RTEMS 4.9.5 On-Line Library

Console Driver Opening a serial device

BSP and Device Driver Development Guide

8.4.5: Opening a serial device

The console_open function is called whenever a serial device is opened. The device registered as "/dev/console" (CONSOLE_DEVICE_NAME) is opened automatically during RTEMS initialization. For instance, if UART channel 2 is registered as "/dev/tty1", the console_open entry point will be called as the result of an fopen("/dev/tty1", mode) in the application.

The console_open function has to inform Termios of the low-level functions for serial line support.

rtems_device_driver console_open(
    rtems_device_major_number major,
    rtems_device_minor_number minor,
    void *arg
)
{
    struct rtems_termios_callbacks *callbacks =
        &my_driver_callbacks_polled;

    /*
     * Check the minor number.  Termios does currently not check
     * the return value of the first open call so the minor
     * number must be checked here.
     */
    if (MY_DRIVER_IS_MINOR_INVALID(minor)) {
        return RTEMS_INVALID_NUMBER;
    }

    /*
     * Depending on the IO mode you need to pass a different set of
     * callback functions to Termios.
     */
    if (MY_DRIVER_USES_INTERRUPTS(minor)) {
        callbacks = &my_driver_callbacks_interrupt;
    }

    return rtems_termios_open(major, minor, arg, callbacks);
}

During the first open of the device Termios will call my_driver_first_open.

static int my_driver_first_open(int major, int minor, void *arg)
{
    my_driver_entry *e = &my_driver_table [minor];
    struct rtems_termios_tty *tty =
        ((rtems_libio_open_close_args_t *) arg)->iop->data1;

    /* Check minor number */
    if (MY_DRIVER_IS_MINOR_INVALID(minor)) {
        return -1;
    }

    /* Connect the TTY data structure */
    e->tty = tty;

    /*
     * You may add some initialization code here.
     */

    /*
     * Sets the inital baud rate.  This should be set to the value of
     * the boot loader.
     */
    return rtems_termios_set_initial_baud(e->tty, MY_DRIVER_BAUD_RATE);
}

BSP and Device Driver Development Guide