commpage_mach_absolute_time.s [plain text]
/*
* Copyright (c) 2003 Apple Computer, Inc. All rights reserved.
*
* @APPLE_LICENSE_HEADER_START@
*
* The contents of this file constitute Original Code as defined in and
* are subject to the Apple Public Source License Version 1.1 (the
* "License"). You may not use this file except in compliance with the
* License. Please obtain a copy of the License at
* http://www.apple.com/publicsource and read it before using this file.
*
* This Original Code and all software distributed under the License are
* distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
* EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
* INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT. Please see the
* License for the specific language governing rights and limitations
* under the License.
*
* @APPLE_LICENSE_HEADER_END@
*/
#include <sys/appleapiopts.h>
#include <machine/cpu_capabilities.h>
#include <machine/commpage.h>
#include <i386/asm.h>
#include <assym.s>
.text
.align 2, 0x90
Lmach_absolute_time:
int $0x3
ret
COMMPAGE_DESCRIPTOR(mach_absolute_time,_COMM_PAGE_ABSOLUTE_TIME,1,0)
Lnanotime:
pushl %ebx
pushl %esi
pushl %edi
pushl %ebp
movl $(_COMM_PAGE_NANOTIME_INFO), %esi
/*
* The nanotime info consists of:
* - base_tsc 64-bit timestamp register value
* - base_ns 64-bit corresponding nanosecond uptime value
* - scale 32-bit current scale multiplier
* - shift 32-bit current shift divider
* - check_tsc 64-bit timestamp check value
*
* This enables an timestamp register's value, tsc, to be converted
* into a nanosecond nanotime value, ns:
*
* ns = base_ns + ((tsc - base_tsc) * scale >> shift)
*
* The kernel updates this every tick or whenever a performance
* speed-step changes the scaling. To avoid locking, a duplicated
* sequence counting scheme is used. The base_tsc value is updated
* whenever the info starts to be changed, and check_tsc is updated
* to the same value at the end of the update. The regularity of
* update ensures that (tsc - base_tsc) is a 32-bit quantity.
* When a conversion is performed, we read base_tsc before we start
* and check_tsc at the end -- if there's a mis-match we repeat.
* It's sufficient to compare only the low-order 32-bits.
*/
1:
//
// Read nanotime info and stash in registers.
//
movl NANOTIME_BASE_TSC(%esi), %ebx // ebx := lo(base_tsc)
movl NANOTIME_BASE_NS(%esi), %ebp
movl NANOTIME_BASE_NS+4(%esi), %edi // edi:ebp := base_ns
movl NANOTIME_SHIFT(%esi), %ecx // ecx := shift
//
// Read timestamp register (tsc) and calculate delta.
//
rdtsc // edx:eax := tsc
subl %ebx, %eax // eax := (tsc - base_tsc)
movl NANOTIME_SCALE(%esi), %edx // edx := shift
//
// Check for consistency and re-read if necessary.
//
cmpl NANOTIME_CHECK_TSC(%esi), %ebx
jne 1b
//
// edx:eax := ((tsc - base_tsc) * scale)
//
mull %edx
//
// eax := ((tsc - base_tsc) * scale >> shift)
//
shrdl %cl, %edx, %eax
andb $32, %cl
cmovnel %edx, %eax // %eax := %edx if shift == 32
xorl %edx, %edx
//
// Add base_ns:
// edx:eax = (base_ns + ((tsc - base_tsc) * scale >> shift))
//
addl %ebp, %eax
adcl %edi, %edx
popl %ebp
popl %edi
popl %esi
popl %ebx
ret
COMMPAGE_DESCRIPTOR(nanotime,_COMM_PAGE_NANOTIME,1,0)