atomicity.h revision 117397 
1// Low-level functions for atomic operations: m68k version -*- C++ -*-
2
3// Copyright (C) 2001, 2002 Free Software Foundation, Inc.
4//
5// This file is part of the GNU ISO C++ Library.  This library is free
6// software; you can redistribute it and/or modify it under the
7// terms of the GNU General Public License as published by the
8// Free Software Foundation; either version 2, or (at your option)
9// any later version.
10
11// This library is distributed in the hope that it will be useful,
12// but WITHOUT ANY WARRANTY; without even the implied warranty of
13// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14// GNU General Public License for more details.
15
16// You should have received a copy of the GNU General Public License along
17// with this library; see the file COPYING.  If not, write to the Free
18// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
19// USA.
20
21// As a special exception, you may use this file as part of a free software
22// library without restriction.  Specifically, if other files instantiate
23// templates or use macros or inline functions from this file, or you compile
24// this file and link it with other files to produce an executable, this
25// file does not by itself cause the resulting executable to be covered by
26// the GNU General Public License.  This exception does not however
27// invalidate any other reasons why the executable file might be covered by
28// the GNU General Public License.
29
30#ifndef _BITS_ATOMICITY_H
31#define _BITS_ATOMICITY_H	1
32
33typedef int _Atomic_word;
34
35#if defined(__mc68020__) || defined(__mc68030__) \
36    || defined(__mc68040__) || defined(__mc68060__)
37// These variants support compare-and-swap.
38
39static inline _Atomic_word
40__attribute__ ((__unused__))
41__exchange_and_add (volatile _Atomic_word *__mem, int __val)
42{
43  register _Atomic_word __result = *__mem;
44  register _Atomic_word __temp;
45  __asm__ __volatile__ ("1: move%.l %0,%1\n\t"
46			"add%.l %2,%1\n\t"
47			"cas%.l %0,%1,%3\n\t"
48			"jne 1b"
49			: "=d" (__result), "=&d" (__temp)
50			: "d" (__val), "m" (*__mem), "0" (__result)
51			: "memory");
52  return __result;
53}
54
55#elif defined(__rtems__)
56  /*
57   * TAS/JBNE is unsafe on systems with strict priority-based scheduling.
58   * Disable interrupts, which we can do only from supervisor mode.
59   */
60static inline _Atomic_word
61__attribute__ ((__unused__))
62__exchange_and_add (volatile _Atomic_word *__mem, int __val)
63{
64  _Atomic_word __result;
65  short __level, __tmpsr;
66  __asm__ __volatile__ ("move%.w %%sr,%0\n\tor%.l %0,%1\n\tmove%.w %1,%%sr"
67                       : "=d"(__level), "=d"(__tmpsr) : "1"(0x700));
68
69  __result = *__mem;
70  *__mem = __result + __val;
71
72  __asm__ __volatile__ ("move%.w %0,%%sr" : : "d"(__level));
73
74  return __result;
75}
76
77#elif !defined(__mcf5200__) && !defined(__mcf5300__)
78// 68000, 68010, cpu32 and 5400 support test-and-set.
79
80template <int __inst>
81struct __Atomicity_lock
82{
83  static volatile unsigned char _S_atomicity_lock;
84};
85
86template <int __inst>
87volatile unsigned char __Atomicity_lock<__inst>::_S_atomicity_lock = 0;
88
89template volatile unsigned char __Atomicity_lock<0>::_S_atomicity_lock;
90
91static inline _Atomic_word
92__attribute__ ((__unused__))
93__exchange_and_add (volatile _Atomic_word *__mem, int __val)
94{
95  _Atomic_word __result;
96
97  __asm__ __volatile__("1: tas %0\n\tjbne 1b"
98		       : "=m"(__Atomicity_lock<0>::_S_atomicity_lock)
99		       : "m"(__Atomicity_lock<0>::_S_atomicity_lock));
100
101  __result = *__mem;
102  *__mem = __result + __val;
103
104  __Atomicity_lock<0>::_S_atomicity_lock = 0;
105
106  return __result;
107}
108
109#elif defined(__vxWorks__) || defined(__embedded__)
110// The best we can hope for is to disable interrupts, which we
111// can only do from supervisor mode.
112
113static inline _Atomic_word
114__attribute__ ((__unused__))
115__exchange_and_add (volatile _Atomic_word *__mem, int __val)
116{
117  _Atomic_word __result;
118  short __level, __tmpsr;
119  __asm__ __volatile__ ("move%.w %%sr,%0\n\tor%.l %0,%1\n\tmove%.w %1,%%sr"
120		  	: "=d"(__level), "=d"(__tmpsr) : "1"(0x700));
121
122  __result = *__mem;
123  *__mem = __result + __val;
124
125  __asm__ __volatile__ ("move%.w %0,%%sr" : : "d"(__level));
126
127  return __result;
128}
129
130#else
131// These variants do not support any atomic operations at all.
132
133#warning "__exchange_and_add is not atomic for this target"
134
135static inline _Atomic_word
136__attribute__ ((__unused__))
137__exchange_and_add (volatile _Atomic_word *__mem, int __val)
138{
139  _Atomic_word __result;
140
141  __result = *__mem;
142  *__mem = __result + __val;
143
144  return __result;
145}
146
147#endif /* CAS / IRQ / TAS */
148
149static inline void
150__attribute__ ((__unused__))
151__atomic_add (volatile _Atomic_word* __mem, int __val)
152{
153  // Careful: using add.l with a memory destination is not
154  // architecturally guaranteed to be atomic.
155  (void) __exchange_and_add (__mem, __val);
156}
157
158#endif /* atomicity.h */
159