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()					  \
670:	movl	RNT_GENERATION(%rdi),%esi				; \
68	test        %esi,%esi		/* info updating? */		; \
69        jz        0b			/* - wait if so */		; \
70	lfence								; \
71	rdtsc								; \
72	lfence								; \
73	shlq	$32,%rdx						; \
74	movl    RNT_SHIFT(%rdi),%ecx					; \
75	orq	%rdx,%rax			/* %rax := tsc */	; \
76	subq	RNT_TSC_BASE(%rdi),%rax		/* tsc - tsc_base */	; \
77	shlq    %cl,%rax						; \
78	movl	RNT_SCALE(%rdi),%ecx					; \
79	mulq	%rcx				/* delta * scale */	; \
80	shrdq	$32,%rdx,%rax			/* %rdx:%rax >>= 32 */	; \
81	addq	RNT_NS_BASE(%rdi),%rax		/* add ns_base */	; \
82	cmpl	RNT_GENERATION(%rdi),%esi	/* repeat if changed */ ; \
83	jne	0b
84
85#endif /* _PAL_RTCLOCK_ASM_NATIVE_H_ */
86