1 /* 2 * Copyright (c) 2010-2012 Apple Inc. All rights reserved. 3 * 4 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@ 5 * 6 * This file contains Original Code and/or Modifications of Original Code 7 * as defined in and that are subject to the Apple Public Source License 8 * Version 2.0 (the 'License'). You may not use this file except in 9 * compliance with the License. The rights granted to you under the License 10 * may not be used to create, or enable the creation or redistribution of, 11 * unlawful or unlicensed copies of an Apple operating system, or to 12 * circumvent, violate, or enable the circumvention or violation of, any 13 * terms of an Apple operating system software license agreement. 14 * 15 * Please obtain a copy of the License at 16 * http://www.opensource.apple.com/apsl/ and read it before using this file. 17 * 18 * The Original Code and all software distributed under the License are 19 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER 20 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, 21 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, 22 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. 23 * Please see the License for the specific language governing rights and 24 * limitations under the License. 25 * 26 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@ 27 */ 28 /* 29 * @OSF_COPYRIGHT@ 30 */ 31 /* 32 * @APPLE_FREE_COPYRIGHT@ 33 */ 34 /* 35 * File: rtclock_asm_native.h 36 * Purpose: Native routines for reading nanotime 37 */ 38 39 #ifndef _PAL_RTCLOCK_ASM_NATIVE_H_ 40 #define _PAL_RTCLOCK_ASM_NATIVE_H_ 41 42 /* 43 * Assembly snippet included in exception handlers and rtc_nanotime_read() 44 * 45 * 46 * Warning! There are several copies of this code in the trampolines found in 47 * osfmk/x86_64/idt64.s, coming from the various TIMER macros in rtclock_asm.h. 48 * They're all kept in sync by using the RTC_NANOTIME_READ() macro. 49 * 50 * The algorithm we use is: 51 * 52 * ns = ((((rdtsc - rnt_tsc_base)<<rnt_shift)*rnt_tsc_scale) / 2**32) + rnt_ns_base; 53 * 54 * rnt_shift, a constant computed during initialization, is the smallest value for which: 55 * 56 * (tscFreq << rnt_shift) > SLOW_TSC_THRESHOLD 57 * 58 * Where SLOW_TSC_THRESHOLD is about 10e9. Since most processor's tscFreqs are greater 59 * than 1GHz, rnt_shift is usually 0. rnt_tsc_scale is also a 32-bit constant: 60 * 61 * rnt_tsc_scale = (10e9 * 2**32) / (tscFreq << rnt_shift); 62 * 63 * %rdi points to nanotime info struct. 64 * %rax returns nanotime 65 */ 66 #define PAL_RTC_NANOTIME_READ_FAST() \ 67 0: movl RNT_GENERATION(%rdi),%esi ; \ 68 test %esi,%esi /* info updating? */ ; \ 69 jz 0b /* - wait if so */ ; \ 70 lfence ; \ 71 rdtsc ; \ 72 shlq $32,%rdx ; \ 73 movl RNT_SHIFT(%rdi),%ecx ; \ 74 orq %rdx,%rax /* %rax := tsc */ ; \ 75 subq RNT_TSC_BASE(%rdi),%rax /* tsc - tsc_base */ ; \ 76 shlq %cl,%rax ; \ 77 movl RNT_SCALE(%rdi),%ecx ; \ 78 mulq %rcx /* delta * scale */ ; \ 79 shrdq $32,%rdx,%rax /* %rdx:%rax >>= 32 */ ; \ 80 addq RNT_NS_BASE(%rdi),%rax /* add ns_base */ ; \ 81 cmpl RNT_GENERATION(%rdi),%esi /* repeat if changed */ ; \ 82 jne 0b 83 84 #define PAL_RTC_NANOTIME_READ_NOBARRIER() \ 85 0: movl RNT_GENERATION(%rdi),%esi ; \ 86 test %esi,%esi /* info updating? */ ; \ 87 jz 0b /* - wait if so */ ; \ 88 rdtsc ; \ 89 shlq $32,%rdx ; \ 90 movl RNT_SHIFT(%rdi),%ecx ; \ 91 orq %rdx,%rax /* %rax := tsc */ ; \ 92 subq RNT_TSC_BASE(%rdi),%rax /* tsc - tsc_base */ ; \ 93 shlq %cl,%rax ; \ 94 movl RNT_SCALE(%rdi),%ecx ; \ 95 mulq %rcx /* delta * scale */ ; \ 96 shrdq $32,%rdx,%rax /* %rdx:%rax >>= 32 */ ; \ 97 addq RNT_NS_BASE(%rdi),%rax /* add ns_base */ ; \ 98 cmpl RNT_GENERATION(%rdi),%esi /* repeat if changed */ ; \ 99 jne 0b 100 101 #endif /* _PAL_RTCLOCK_ASM_NATIVE_H_ */ 102