RTEMS 4.10.0 On-Line Library

Frame Buffer Driver Opening the Frame Buffer Device

BSP and Device Driver Development Guide

17.2.2: Opening the Frame Buffer Device

The frame_buffer_open() function is called whenever a frame buffer device is opened. If the frame buffer is registered as "/dev/fb0", the frame_buffer_open entry point will be called as the result of an open("/dev/fb0", mode) in the application.

Thread safety of the frame buffer driver is implementation-dependent. The VGA driver shown below uses a mutex to prevent multiple open() operations of the frame buffer device.

The frame_buffer_open() function returns RTEMS_SUCCESSFUL when the device driver is successfully opened, and RTEMS_UNSATISFIED if the device is already open:

rtems_device_driver frame_buffer_close(
  rtems_device_major_number  major,
  rtems_device_minor_number  minor,
  void                      *arg
)
{
  if (pthread_mutex_unlock(&mutex) == 0){
    /* restore previous state.  for VGA this means return to text mode.
     * leave out if graphics hardware has been initialized in
     * frame_buffer_initialize() */
    ega_hwterm();
    printk( "FBVGA close called.\n" );
    return RTEMS_SUCCESSFUL;
  }

  return RTEMS_UNSATISFIED;
}

In the previous example, the function ega_hwinit() takes care of hardware-specific initialization.

BSP and Device Driver Development Guide