136 lines
4.8 KiB
ArmAsm
136 lines
4.8 KiB
ArmAsm
/*-
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* Copyright (c) 1993 The Regents of the University of California.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the University of
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* California, Berkeley and its contributors.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* $Id: microtime.s,v 1.2 1993/05/22 07:59:54 cgd Exp $
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*/
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#include "asm.h"
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#include "../isa/isa.h"
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#include "../isa/timerreg.h"
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/*
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* Use a higher resolution version of microtime if HZ is not
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* overridden (i.e. it is 100Hz).
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*/
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#ifndef HZ
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ENTRY(microtime)
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pushl %edi
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pushl %esi
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pushl %ebx
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movl $_time,%ebx
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cli # disable interrupts
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movl (%ebx),%edi # sec = time.tv_sec
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movl 4(%ebx),%esi # usec = time.tv_usec
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movl $(TIMER_SEL0|TIMER_LATCH),%eax
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outb %al,$TIMER_MODE # latch timer 0's counter
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#
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# Read counter value into ebx, LSB first
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#
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inb $TIMER_CNTR0,%al
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movzbl %al,%ebx
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inb $TIMER_CNTR0,%al
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movzbl %al,%eax
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sall $8,%eax
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orl %eax,%ebx
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#
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# Now check for counter overflow. This is tricky because the
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# timer chip doesn't let us atomically read the current counter
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# value and the output state (i.e., overflow state). We have
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# to read the ICU interrupt request register (IRR) to see if the
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# overflow has occured. Because we lack atomicity, we use
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# the (very accurate) heuristic that we only check for
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# overflow if the value read is close to the interrupt period.
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# E.g., if we just checked the IRR, we might read a non-overflowing
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# value close to 0, experience overflow, then read this overflow
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# from the IRR, and mistakenly add a correction to the "close
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# to zero" value.
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#
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# We compare the counter value to heuristic constant 11890.
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# If the counter value is less than this, we assume the counter
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# didn't overflow between disabling interrupts above and latching
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# the counter value. For example, we assume that the above 10 or so
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# instructions take less than 11932 - 11890 = 42 microseconds to
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# execute.
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#
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# Otherwise, the counter might have overflowed. We check for this
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# condition by reading the interrupt request register out of the ICU.
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# If it overflowed, we add in one clock period.
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#
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# The heuristic is "very accurate" because it works 100% if
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# we're called from an ipl less than the clock. Otherwise,
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# it might not work. Currently, only gettimeofday and bpf
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# call microtime so it's not a problem.
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#
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cmpl $11890,%ebx
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jle 2f
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movl $0x0a,%eax # tell ICU we want IRR
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outb %al,$IO_ICU1
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inb $IO_ICU1,%al # read IRR in ICU
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testb $1,%al # is a timer interrupt pending?
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je 1f
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addl $-11932,%ebx # yes, subtract one clock period
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1:
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movl $0x0b,%eax # tell ICU we want ISR
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outb %al,$IO_ICU1 # (rest of kernel expects this)
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2:
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sti # enable interrupts
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movl $11932,%eax # subtract counter value from 11932 since
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subl %ebx,%eax # it is a count-down value
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imull $1000,%eax,%eax
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movl $0,%edx # zero extend eax for div
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movl $1193,%ecx
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idivl %ecx # convert to usecs: mult by 1000/1193
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addl %eax,%esi # add counter usecs to time.tv_usec
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cmpl $1000000,%esi # carry in timeval?
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jl 3f
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subl $1000000,%esi # adjust usec
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incl %edi # bump sec
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3:
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movl 16(%esp),%ecx # load timeval pointer arg
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movl %edi,(%ecx) # tvp->tv_sec = sec
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movl %esi,4(%ecx) # tvp->tv_usec = usec
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popl %ebx # restore regs
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popl %esi
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popl %edi
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ret
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#endif
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