diff options
Diffstat (limited to 'sys/i386/i386/microtime.s')
| -rw-r--r-- | sys/i386/i386/microtime.s | 135 |
1 files changed, 135 insertions, 0 deletions
diff --git a/sys/i386/i386/microtime.s b/sys/i386/i386/microtime.s new file mode 100644 index 0000000..4af938b --- /dev/null +++ b/sys/i386/i386/microtime.s @@ -0,0 +1,135 @@ +/*- + * 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 |
