Subversion Repositories openrisc_2011-10-31

/*

 *  This routine is a simple spin delay

 *

 *  Author: Ralf Corsepius (corsepiu@faw.uni-ulm.de)

 *

 *  COPYRIGHT (c) 1999, Ralf Corsepius, Ulm, Germany

 *

 *  This program is distributed in the hope that it will be useful,

 *  but WITHOUT ANY WARRANTY; without even the implied warranty of

 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

 *

 *

 *  COPYRIGHT (c) 1989-1999.

 *  On-Line Applications Research Corporation (OAR).

 *  Copyright assigned to U.S. Government, 1994.

 *

 *  The license and distribution terms for this file may be

 *  found in the file LICENSE in this distribution or at

 *  http://www.OARcorp.com/rtems/license.html.

 *

 *  $Id: delay.c,v 1.2 2001-09-27 12:01:31 chris Exp $

 */

#include <rtems.h>

/*

 *  Simple spin delay in microsecond units for device drivers.

 *  This is very dependent on the clock speed of the target.

 *

 *  Since we don't have a real time clock, this is a very rough

 *  approximation, assuming that each cycle of the delay loop takes

 *  approx. 4 machine cycles.

 *

 *  e.g.: clicks_per_second = 20MHz

 *        => 5e-8 secs per instruction

 *        => 4 * 5e-8 secs per delay loop

 */

void CPU_delay( unsigned32 microseconds )

{

  register unsigned32 clicks_per_usec =

    rtems_cpu_configuration_get_clicks_per_second() / 1000000 ;

  register unsigned32 _delay =

    (microseconds) * (clicks_per_usec);

  asm volatile (

"0:     add  #-4,%0\n

        nop\n

        cmp/pl %0\n

        bt 0b

        nop"

     :: "r" (_delay) );

}