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/*-
* 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.
*
* $Header$
*/
#include "asm.h"
#include "../isa/isa.h"
#include "../isa/timerreg.h"
/*
* Use a higher resolution version of microtime if HZ is not
* overridden (i.e. it is 100Hz).
*/
#ifndef HZ
ENTRY(microtime)
pushl %edi
pushl %esi
pushl %ebx
movl $_time,%ebx
cli # disable interrupts
movl (%ebx),%edi # sec = time.tv_sec
movl 4(%ebx),%esi # usec = time.tv_usec
movl $(TIMER_SEL0|TIMER_LATCH),%eax
outb %al,$TIMER_MODE # latch timer 0's counter
#
# Read counter value into ebx, LSB first
#
inb $TIMER_CNTR0,%al
movzbl %al,%ebx
inb $TIMER_CNTR0,%al
movzbl %al,%eax
sall $8,%eax
orl %eax,%ebx
#
# 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 occured. Because we lack atomicity, we use
# the (very accurate) heuristic that we only check for
# overflow if the value read is close to the interrupt period.
# 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 heuristic constant 11890.
# If the counter value is less than this, we assume the counter
# didn't overflow between disabling interrupts above and latching
# the counter value. For example, we assume that the above 10 or so
# instructions take less than 11932 - 11890 = 42 microseconds to
# execute.
#
# 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.
#
# The heuristic is "very accurate" because it works 100% if
# we're called from an ipl less than the clock. Otherwise,
# it might not work. Currently, only gettimeofday and bpf
# call microtime so it's not a problem.
#
cmpl $11890,%ebx
jle 2f
movl $0x0a,%eax # tell ICU we want IRR
outb %al,$IO_ICU1
inb $IO_ICU1,%al # read IRR in ICU
testb $1,%al # is a timer interrupt pending?
je 1f
addl $-11932,%ebx # yes, subtract one clock period
1:
movl $0x0b,%eax # tell ICU we want ISR
outb %al,$IO_ICU1 # (rest of kernel expects this)
2:
sti # enable interrupts
movl $11932,%eax # subtract counter value from 11932 since
subl %ebx,%eax # it is a count-down value
imull $1000,%eax,%eax
movl $0,%edx # zero extend eax for div
movl $1193,%ecx
idivl %ecx # convert to usecs: mult by 1000/1193
addl %eax,%esi # add counter usecs to time.tv_usec
cmpl $1000000,%esi # carry in timeval?
jl 3f
subl $1000000,%esi # adjust usec
incl %edi # bump sec
3:
movl 16(%esp),%ecx # load timeval pointer arg
movl %edi,(%ecx) # tvp->tv_sec = sec
movl %esi,4(%ecx) # tvp->tv_usec = usec
popl %ebx # restore regs
popl %esi
popl %edi
ret
#endif
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