1/*
2 * Copyright (c) 2003-2007 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#include <sys/appleapiopts.h>
30#include <machine/cpu_capabilities.h>
31
32#if defined(__i386__)
33
34/* return mach_absolute_time in %edx:%eax
35 *
36 * The algorithm we use is:
37 *
38 *	ns = ((((rdtsc - rnt_tsc_base)<<rnt_shift)*rnt_tsc_scale) / 2**32) + rnt_ns_base;
39 *
40 * rnt_shift, a constant computed during initialization, is the smallest value for which:
41 *
42 *  (tscFreq << rnt_shift) > SLOW_TSC_THRESHOLD
43 *
44 * Where SLOW_TSC_THRESHOLD is about 10e9.  Since most processor's tscFreq is greater
45 * than 1GHz, rnt_shift is usually 0.  rnt_tsc_scale is also a 32-bit constant:
46 *
47 *	rnt_tsc_scale = (10e9 * 2**32) / (tscFreq << rnt_shift);
48 */
49
50	.globl _mach_absolute_time
51_mach_absolute_time:
52	pushl	%ebp
53	movl	%esp,%ebp
54	pushl	%esi
55	pushl	%ebx
56
570:
58	movl	_COMM_PAGE_NT_GENERATION,%esi	/* get generation (0 if being changed) */
59	testl	%esi,%esi			/* if being updated, loop until stable */
60	jz	0b
61
62	lfence
63	rdtsc					/* get TSC in %edx:%eax */
64	lfence
65
66	subl	_COMM_PAGE_NT_TSC_BASE,%eax
67	sbbl	_COMM_PAGE_NT_TSC_BASE+4,%edx
68
69    /*
70     * Prior to supporting "slow" processors, xnu always set _NT_SHIFT to 32.
71     * Now it defaults to 0, unless the processor is slow.  The shifts
72     * below implicitly mask the count down to 5 bits, handling either default.
73     */
74	movl    _COMM_PAGE_NT_SHIFT,%ecx
75	shldl   %cl,%eax,%edx			/* shift %edx left, filling in from %eax */
76	shll    %cl,%eax			/* finish shifting %edx:%eax left by _COMM_PAGE_NT_SHIFT bits */
77
78	movl	_COMM_PAGE_NT_SCALE,%ecx
79
80	movl	%edx,%ebx
81	mull	%ecx
82	movl	%ebx,%eax
83	movl	%edx,%ebx
84	mull	%ecx
85	addl	%ebx,%eax
86	adcl	$0,%edx
87
88	addl	_COMM_PAGE_NT_NS_BASE,%eax
89	adcl	_COMM_PAGE_NT_NS_BASE+4,%edx
90
91	cmpl	_COMM_PAGE_NT_GENERATION,%esi	/* have the parameters changed? */
92	jne	0b				/* yes, loop until stable */
93
94	popl	%ebx
95	popl	%esi
96	popl	%ebp
97	ret
98
99#elif defined(__x86_64__)
100
101/*
102 * 64-bit version _mach_absolute_time.  We return the 64-bit nanotime in %rax.
103 *
104 * The algorithm we use is:
105 *
106 *	ns = ((((rdtsc - rnt_tsc_base)<<rnt_shift)*rnt_tsc_scale) / 2**32) + rnt_ns_base;
107 *
108 * rnt_shift, a constant computed during initialization, is the smallest value for which:
109 *
110 *	tscFreq << rnt_shift) > SLOW_TSC_THRESHOLD
111 *
112 * Where SLOW_TSC_THRESHOLD is about 10e9.  Since most processor's tscFreqs are greater
113 * than 1GHz, rnt_shift is usually 0.  rnt_tsc_scale is also a 32-bit constant:
114 *
115 *	rnt_tsc_scale = (10e9 * 2**32) / (tscFreq << rnt_shift);
116 *
117 */
118	.globl	_mach_absolute_time
119_mach_absolute_time:
120	pushq	%rbp				// set up a frame for backtraces
121	movq	%rsp,%rbp
122	movq	$(_COMM_PAGE_TIME_DATA_START),%rsi
1231:
124	movl	_NT_GENERATION(%rsi),%r8d	// get generation
125	testl	%r8d,%r8d			// if 0, data is being changed...
126	jz      1b				// ...so loop until stable
127	lfence
128	rdtsc					// edx:eax := tsc
129	lfence
130	shlq	$32,%rdx			// rax := ((edx << 32) | eax), ie 64-bit tsc
131	orq     %rdx,%rax
132
133    /*
134     * Prior to supporting "slow" processors, xnu always set _NT_SHIFT to 32.
135     * Now it defaults to 0, unless the processor is slow.  In order to maintain
136     * compatibility with both old and new versions of xnu, we mask the shift
137     * down to 0x1F, which maps the old default (32) into the new default (0).
138     */
139	movl    _NT_SHIFT(%rsi),%ecx
140	andl    $0x1F,%ecx			// *** remove this line once 10.9 is GM ***
141	subq	_NT_TSC_BASE(%rsi), %rax	// rax := (tsc - base_tsc)
142	shlq    %cl,%rax			// rax := (tsc - base_tsc) << NT_SHIFT
143	movl	_NT_SCALE(%rsi),%ecx
144	mulq	%rcx				// rdx:rax := ((tsc - base_tsc)<<shift) * scale
145	shrdq	$32,%rdx,%rax			// divide by 2**32
146	addq	_NT_NS_BASE(%rsi),%rax		// (((tsc - base_tsc) * scale) >> 32) + ns_base
147
148	cmpl	_NT_GENERATION(%rsi),%r8d	// did the data change during computation?
149	jne     1b
150	popq	%rbp
151	ret
152
153#else
154#error Unsupported architecture
155#endif
156