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/* $OpenBSD: microtime.s,v 1.15 2002/07/06 19:14:20 nordin Exp $ */
/* $NetBSD: microtime.s,v 1.16 1995/04/17 12:06:47 cgd Exp $ */
/*-
* Copyright (c) 1993 The Regents of the University of California.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WArRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <machine/asm.h>
#include <dev/isa/isareg.h>
#include <i386/isa/timerreg.h>
#define IRQ_BIT(irq_num) (1 << ((irq_num) % 8))
#define IRQ_BYTE(irq_num) ((irq_num) / 8)
/*
* Use a higher resolution version of microtime if HZ is not
* overridden (i.e. it is 100Hz).
*/
#ifndef HZ
ENTRY(microtime)
xorl %ecx,%ecx
movb $(TIMER_SEL0|TIMER_LATCH),%al
pushfl
cli # disable interrupts
outb %al,$TIMER_MODE # latch timer 0's counter
# Read counter value into ecx, LSB first
xorl %ecx,%ecx
inb $TIMER_CNTR0,%al
movb %al,%cl
inb $TIMER_CNTR0,%al
movb %al,%ch
# Now check for counter overflow. This is tricky because the
# timer chip doesn't let us atomically read the current counter
# value and the output state (i.e., overflow state). We have
# to read the ICU interrupt request register (IRR) to see if the
# overflow has occurred. Because we lack atomicity, we use
# the (very accurate) heuristic that we do not check for
# overflow if the value read is close to 0.
# E.g., if we just checked the IRR, we might read a non-overflowing
# value close to 0, experience overflow, then read this overflow
# from the IRR, and mistakenly add a correction to the "close
# to zero" value.
#
# We compare the counter value to the heuristic constant 12.
# If the counter value is less than this, we assume the counter
# didn't overflow between disabling clock interrupts and latching
# the counter value above. For example, we assume that the first 3
# instructions take less than 12 microseconds to execute.
#
# (We used to check for overflow only if the value read was close to
# the timer limit, but this doesn't work very well if we're at the
# clock's ipl or higher.)
#
# Otherwise, the counter might have overflowed. We check for this
# condition by reading the interrupt request register out of the ICU.
# If it overflowed, we add in one clock period.
movl $11932,%edx # counter limit
testb $IRQ_BIT(0),_ipending + IRQ_BYTE(0)
jnz 1f
cmpl $12,%ecx # check for potential overflow
jbe 2f
inb $IO_ICU1,%al # read IRR in ICU
testb $IRQ_BIT(0),%al # is a timer interrupt pending?
jz 2f
1: subl %edx,%ecx # add another tick
2: subl %ecx,%edx # subtract counter value from counter limit
# Divide by 1193280/1000000. We use a fast approximation of 4096/3433.
# For values of hz more than 100, this has a maximum error of 2us.
leal (%edx,%edx,2),%eax # a = 3d
leal (%edx,%eax,4),%eax # a = 4a + d = 13d
movl %eax,%ecx
shll $5,%ecx
addl %ecx,%eax # a = 33a = 429d
leal (%edx,%eax,8),%eax # a = 8a + d = 3433d
shrl $12,%eax # a = a/4096 = 3433d/4096
common_microtime:
movl _time,%edx # get time.tv_sec
addl _time+4,%eax # add time.tv_usec
popfl # enable interrupts
cmpl $1000000,%eax # carry in timeval?
jb 3f
subl $1000000,%eax # adjust usec
incl %edx # bump sec
3: movl 4(%esp),%ecx # load timeval pointer arg
movl %edx,(%ecx) # tvp->tv_sec = sec
movl %eax,4(%ecx) # tvp->tv_usec = usec
ret
#if defined(I586_CPU) || defined(I686_CPU)
# XXX: Move to machdep.c?
.data
.globl _pentium_base_tsc
.comm _pentium_base_tsc,8
.text
#endif
#endif
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