i8254.c revision 7c478bd95313f5f23a4c958a745db2134aa03244
/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License, Version 1.0 only
* (the "License"). You may not use this file except in compliance
* with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright 2004 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
*/
/* Copyright (c) 1990, 1991 UNIX System Laboratories, Inc. */
/* Copyright (c) 1984, 1986, 1987, 1988, 1989, 1990 AT&T */
/* All Rights Reserved */
#pragma ident "%Z%%M% %I% %E% SMI"
#include <sys/machlock.h>
#include <sys/smp_impldefs.h>
#include <sys/archsystm.h>
#include <sys/machsystm.h>
#define MICROCOUNT 0x2000
#ifdef _SIMULATOR_SUPPORT
extern int simulator_run; /* if non-zero then running under simulator */
#endif /* _SIMULATOR_SUPPORT */
void
microfind(void)
{
/*
* The algorithm tries to guess a loop count for tenmicrosec such
* that found will be 0xf000 PIT counts, but because it is only a
* rough guess there is no guarantee that tenmicrosec will take
* exactly 0xf000 PIT counts. min is set initially to 0xe000 and
* represents the number of PIT counts that must elapse in
* tenmicrosec for microfind to calculate the correct loop count for
* tenmicrosec. The algorith will successively set count to better
* approximations until the number of PIT counts elapsed are greater
* than min. Ideally the first guess should be correct, but as cpu's
* become faster MICROCOUNT may have to be increased to ensure
* that the first guess for count is correct. There is no harm
* leaving MICRCOUNT at 0x2000, the results will be correct, it just
* may take longer to calculate the correct value for the loop
* count used by tenmicrosec. In some cases min may be reset as the
* algorithm progresses in order to facilitate faster cpu's.
*/
int s;
unsigned char status;
#ifdef _SIMULATOR_SUPPORT
if (simulator_run) {
return;
}
#endif /* _SIMULATOR_SUPPORT */
s = clear_int_flag(); /* disable interrupts */
/*CONSTCOND*/
while (1) {
/*
* microdata is the loop count used in tenmicrosec. The first
* time around microdata is set to 1 to make tenmicrosec
* return quickly. The purpose of this while loop is to
* warm the cache for the next time around when the number
* of PIT counts are measured.
*/
microdata = 1;
/*CONSTCOND*/
while (1) {
/* Put counter 0 in mode 0 */
/* output a count of -1 to counter 0 */
tenmicrosec();
/* READ BACK counter 0 to latch status and count */
/* Read status of counter 0 */
/* Read the value left in the counter */
if (microdata != 1)
break;
}
/* verify that the counter began the count-down */
/* microdata is too small */
/*
* If the cpu is so fast that it cannot load the
* counting element of the PIT with a very large
* value for the loop used in tenmicrosec, then
* the algorithm will not work for this cpu.
* It is very unlikely there will ever be such
* an x86.
*/
if (count > 0x100000000)
panic("microfind: cpu is too fast");
continue;
}
/* verify that the counter did not wrap around */
/*
* microdata is too large. Since there are counts
* that would have been appropriate for the PIT
* not to wrap on even a lowly AT, count will never
* decrease to 1.
*/
continue;
}
/* mode 0 is an n + 1 counter */
break;
/* verify that the cpu is slow enough to count to 0xf000 */
count *= 0xf000;
/*
* It is possible that at some point cpu's will become
* sufficiently fast such that the PIT will not be able to
* count to 0xf000 within the maximum loop count used in
* tenmicrosec. In that case the loop count in tenmicrosec
* may be set to the maximum value because it is unlikely
* that the cpu will be so fast that tenmicrosec with the
* maximum loop count will take more than ten microseconds.
* If the cpu is indeed too fast for the current
* implementation of tenmicrosec, then there is code below
* intended to catch that situation.
*/
/* cpu is fast, just make it count as high it can */
count = 0x100000000;
min = 0;
continue;
}
/*
* Count in the neighborhood of 0xf000 next time around
* There is no risk of dividing by zero since found is in the
* range of 0x1 to 0x1000.
*/
}
/*
* Formula for delaycount is :
* (loopcount * timer clock speed) / (counter ticks * 1000)
* Note also that 1000 is for figuring out milliseconds
*/
if (count >= 0x100000001)
/*
* This cpu is too fast for the current implementation of
* tenmicrosec. It is unlikely such a fast x86 will exist.
*/
panic("microfind: cpu is too fast");
if (count != 0)
else
microdata = 1;
/* Restore timer channel 0 for BIOS use */
/* write mode to 3, square-wave */
/* write 16 bits of 0 for initial count */
outb(PITCTR0_PORT, 0);
outb(PITCTR0_PORT, 0);
restore_int_flag(s); /* restore interrupt state */
}