1/*
2 * Copyright (c) 2010 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#if defined(__i386__)
44/*
45 * Assembly snippet included in exception handlers and rtc_nanotime_read()
46 * %edi points to nanotime info struct
47 * %edx:%eax returns nanotime
48 */
49#define PAL_RTC_NANOTIME_READ_FAST()					  \
500:	movl	RNT_GENERATION(%edi),%esi	/* being updated? */	; \
51	testl	%esi,%esi						; \
52	jz	0b				/* wait until done */	; \
53	lfence								; \
54	rdtsc								; \
55	lfence								; \
56	subl	RNT_TSC_BASE(%edi),%eax					; \
57	sbbl	RNT_TSC_BASE+4(%edi),%edx	/* tsc - tsc_base */	; \
58	movl	RNT_SCALE(%edi),%ecx		/* * scale factor */	; \
59	movl	%edx,%ebx						; \
60	mull	%ecx							; \
61	movl	%ebx,%eax						; \
62	movl	%edx,%ebx						; \
63	mull	%ecx							; \
64	addl	%ebx,%eax						; \
65	adcl	$0,%edx							; \
66	addl	RNT_NS_BASE(%edi),%eax		/* + ns_base */		; \
67	adcl	RNT_NS_BASE+4(%edi),%edx				; \
68	cmpl	RNT_GENERATION(%edi),%esi	/* check for update */	; \
69	jne	0b				/* do it all again */
70
71#elif defined(__x86_64__)
72
73/*
74 * Assembly snippet included in exception handlers and rtc_nanotime_read()
75 *
76 *
77 * Warning!  There are several copies of this code in the trampolines found in
78 * osfmk/x86_64/idt64.s, coming from the various TIMER macros in rtclock_asm.h.
79 * They're all kept in sync by using the RTC_NANOTIME_READ() macro.
80 *
81 * The algorithm we use is:
82 *
83 *	ns = ((((rdtsc - rnt_tsc_base)<<rnt_shift)*rnt_tsc_scale) / 2**32) + rnt_ns_base;
84 *
85 * rnt_shift, a constant computed during initialization, is the smallest value for which:
86 *
87 *	(tscFreq << rnt_shift) > SLOW_TSC_THRESHOLD
88 *
89 * Where SLOW_TSC_THRESHOLD is about 10e9.  Since most processor's tscFreqs are greater
90 * than 1GHz, rnt_shift is usually 0.  rnt_tsc_scale is also a 32-bit constant:
91 *
92 *	rnt_tsc_scale = (10e9 * 2**32) / (tscFreq << rnt_shift);
93 *
94 * %rdi points to nanotime info struct.
95 * %rax returns nanotime
96 */
97#define PAL_RTC_NANOTIME_READ_FAST()					  \
980:	movl	RNT_GENERATION(%rdi),%esi				; \
99	test        %esi,%esi		/* info updating? */		; \
100        jz        0b			/* - wait if so */		; \
101	lfence								; \
102	rdtsc								; \
103	lfence								; \
104	shlq	$32,%rdx						; \
105	movl    RNT_SHIFT(%rdi),%ecx					; \
106	orq	%rdx,%rax			/* %rax := tsc */	; \
107	subq	RNT_TSC_BASE(%rdi),%rax		/* tsc - tsc_base */	; \
108	shlq    %cl,%rax						; \
109	movl	RNT_SCALE(%rdi),%ecx					; \
110	mulq	%rcx				/* delta * scale */	; \
111	shrdq	$32,%rdx,%rax			/* %rdx:%rax >>= 32 */	; \
112	addq	RNT_NS_BASE(%rdi),%rax		/* add ns_base */	; \
113	cmpl	RNT_GENERATION(%rdi),%esi	/* repeat if changed */ ; \
114	jne	0b
115
116#endif /* !defined(x86_64) */
117
118
119#endif /* _PAL_RTCLOCK_ASM_NATIVE_H_ */
120