gensh1/clock/delay.c

0001 /*
0002  *  This routine is a simple spin delay
0003  *
0004  *  Author: Ralf Corsepius (corsepiu@faw.uni-ulm.de)
0005  *
0006  *  COPYRIGHT (c) 1999, Ralf Corsepius, Ulm, Germany
0007  *
0008  *  This program is distributed in the hope that it will be useful,
0009  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
0010  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
0011  *
0012  *
0013  *  COPYRIGHT (c) 1989-1999.
0014  *  On-Line Applications Research Corporation (OAR).
0015  *
0016  *  The license and distribution terms for this file may be
0017  *  found in the file LICENSE in this distribution or at
0018  *  http://www.rtems.org/license/LICENSE.
0019  */
0020
0021
0022 #include <rtems.h>
0023
0024 extern uint32_t bsp_clicks_per_second;
0025
0026 /*
0027  *  Simple spin delay in microsecond units for device drivers.
0028  *  This is very dependent on the clock speed of the target.
0029  *
0030  *  Since we don't have a real time clock, this is a very rough
0031  *  approximation, assuming that each cycle of the delay loop takes
0032  *  approx. 4 machine cycles.
0033  *
0034  *  e.g.: clicks_per_second = 20MHz
0035  *        => 5e-8 secs per instruction
0036  *        => 4 * 5e-8 secs per delay loop
0037  */
0038
0039 void CPU_delay( uint32_t   microseconds )
0040 {
0041   register uint32_t   clicks_per_usec = bsp_clicks_per_second / 1000000;
0042   register uint32_t   _delay = (microseconds) * (clicks_per_usec);
0043
0044   __asm__ volatile (
0045 "0: add  #-4,%0\n\
0046     nop\n\
0047     cmp/pl %0\n\
0048     bt 0b\n\
0049     nop"
0050      :: "r" (_delay) );
0051 }