mach_absolute_time_asm.s [plain text]
/*
* Copyright (c) 2003-2007 Apple Inc. All rights reserved.
*
* @APPLE_OSREFERENCE_LICENSE_HEADER_START@
*
* This file contains Original Code and/or Modifications of Original Code
* as defined in and that are subject to the Apple Public Source License
* Version 2.0 (the 'License'). You may not use this file except in
* compliance with the License. The rights granted to you under the License
* may not be used to create, or enable the creation or redistribution of,
* unlawful or unlicensed copies of an Apple operating system, or to
* circumvent, violate, or enable the circumvention or violation of, any
* terms of an Apple operating system software license agreement.
*
* Please obtain a copy of the License at
* http://www.opensource.apple.com/apsl/ and read it before using this file.
*
* The 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, QUIET ENJOYMENT OR NON-INFRINGEMENT.
* Please see the License for the specific language governing rights and
* limitations under the License.
*
* @APPLE_OSREFERENCE_LICENSE_HEADER_END@
*/
#include <sys/appleapiopts.h>
#include <machine/cpu_capabilities.h>
/* return mach_absolute_time in %edx:%eax
*
* The algorithm we use is:
*
* ns = ((((rdtsc - rnt_tsc_base)<<rnt_shift)*rnt_tsc_scale) / 2**32) + rnt_ns_base * rnt_shift, a constant computed during initialization, is the smallest value for which:
*
* (tscFreq << rnt_shift) > SLOW_TSC_THRESHOLD
*
* Where SLOW_TSC_THRESHOLD is about 10e9. Since most processor's tscFreq is greater
* than 1GHz, rnt_shift is usually 0. rnt_tsc_scale is also a 32-bit constant:
*
* rnt_tsc_scale = (10e9 * 2**32) / (tscFreq << rnt_shift)
.globl _mach_absolute_time
_mach_absolute_time:
pushl %ebp
movl %esp,%ebp
pushl %esi
pushl %ebx
0:
movl _COMM_PAGE_NT_GENERATION,%esi /* get generation (0 if being changed) */
testl %esi,%esi /* if being updated, loop until stable */
jz 0b
lfence
rdtsc /* get TSC in %edx:%eax */
lfence
subl _COMM_PAGE_NT_TSC_BASE,%eax
sbbl _COMM_PAGE_NT_TSC_BASE+4,%edx
/*
* Prior to supporting "slow" processors, xnu always set _NT_SHIFT to 32.
* Now it defaults to 0, unless the processor is slow. The shifts
* below implicitly mask the count down to 5 bits, handling either default.
*/
movl _COMM_PAGE_NT_SHIFT,%ecx
shldl %cl,%eax,%edx /* shift %edx left, filling in from %eax */
shll %cl,%eax /* finish shifting %edx:%eax left by _COMM_PAGE_NT_SHIFT bits */
movl _COMM_PAGE_NT_SCALE,%ecx
movl %edx,%ebx
mull %ecx
movl %ebx,%eax
movl %edx,%ebx
mull %ecx
addl %ebx,%eax
adcl $0,%edx
addl _COMM_PAGE_NT_NS_BASE,%eax
adcl _COMM_PAGE_NT_NS_BASE+4,%edx
cmpl _COMM_PAGE_NT_GENERATION,%esi /* have the parameters changed? */
jne 0b /* yes, loop until stable */
popl %ebx
popl %esi
popl %ebp
ret