osx man page for request_refresh_rate

request_refresh_rate(3alleg4)					  Allegro manual				     request_refresh_rate(3alleg4)

NAME
       request_refresh_rate - Requests a specific refresh rate during graphic mode switch. Allegro game programming library.

SYNOPSIS
       #include <allegro.h>

       void request_refresh_rate(int rate);

DESCRIPTION
       Requests  that the next call to set_gfx_mode() try to use the specified refresh rate, if possible. Not all drivers are able to control this
       at all, and even when they can, not all rates will be possible on all hardware, so the actual settings may differ from what you	requested.
       After  you call set_gfx_mode(), you can use get_refresh_rate() to find out what was actually selected. At the moment only the DOS VESA 3.0,
       X DGA 2.0 and some Windows DirectX drivers support this function. The speed is specified in Hz, eg. 60, 70. To return to the normal default
       selection, pass a rate value of zero. Example:

	  request_refresh_rate(60);
	  if (set_gfx_mode(GFX_AUTODETECT, 640, 480, 0, 0) != 0)
	     abort_on_error("Couldn't set graphic mode!");
	  if (get_refresh_rate() != 60)
	     abort_on_error("Couldn't set refresh rate to 60Hz!");

SEE ALSO
       set_gfx_mode(3alleg4), get_refresh_rate(3alleg4)

Allegro 							   version 4.4.2				     request_refresh_rate(3alleg4)