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/*
* 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).
*
* The license and distribution terms for this file may be
* found in the file LICENSE in this distribution or at
* http://www.rtems.com/license/LICENSE.
*
* $Id$
*/
#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\n\
nop"
:: "r" (_delay) );
}
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