1 | ////////////////////////////////////////////////////////////////////////////////// |
---|
2 | // File : mwmr.c |
---|
3 | // Date : 01/04/2012 |
---|
4 | // Author : alain greiner |
---|
5 | // Copyright (c) UPMC-LIP6 |
---|
6 | /////////////////////////////////////////////////////////////////////////////////// |
---|
7 | // The mwmr.c and mwmr.h files are part of the GIET nano-kernel. |
---|
8 | // This middlewre implements a user level Multi-Writers / Multi-Readers |
---|
9 | // communication channel, that can be sued by parallel multi-tasks applications |
---|
10 | // respecting the TCG (Tasks and Communications Graph) formalism. |
---|
11 | // |
---|
12 | // The mwmr_read() and mwmr_write() functions do not require a system call, |
---|
13 | // |
---|
14 | // The mwmr_get_base() returns the virtual base address of the MWMR channel. |
---|
15 | // As this function requires a system call, it is defined in the stdio.c and |
---|
16 | // stdio.h files. |
---|
17 | // |
---|
18 | // ALL MWMR channels must be defined in the mapping_info data structure, |
---|
19 | // to be initialised by the GIET in the boot phase. |
---|
20 | // The max number of words that can be stored in a MWMR channel is defined by the |
---|
21 | // depth parameter, but all MWMR channels are implemented as fixed size buffers, |
---|
22 | // and the size is defined by the GIET_MWMR_SIZE_MAX configuration parameter. |
---|
23 | // An MWMR transaction is an integer number of unsigned int (32 bits mwords). |
---|
24 | // Both the mwmr_read() and mwmr_write() functions are blocking functions. |
---|
25 | // A private lock provides exclusive access to the MWMR channel, that can have |
---|
26 | // a variable number of producers and a variable number of consumers. |
---|
27 | /////////////////////////////////////////////////////////////////////////////////// |
---|
28 | |
---|
29 | #include <mwmr.h> |
---|
30 | #include <stdio.h> |
---|
31 | |
---|
32 | /////////////////////////////////////////////////////////////////////////////////// |
---|
33 | // mwmr_lock_acquire() |
---|
34 | // We use a fixed delay befor retry, in order to avoid the system call |
---|
35 | // associated to the rand() function. |
---|
36 | // This is probably a weakness, that can be improved... |
---|
37 | /////////////////////////////////////////////////////////////////////////////////// |
---|
38 | inline void mwmr_lock_acquire(unsigned int* lock) |
---|
39 | { |
---|
40 | asm volatile ( |
---|
41 | "lock_try: \n" |
---|
42 | "ll $2, 0(%0) \n" /* $2 <= lock current value */ |
---|
43 | "bnez $2, lock_delay \n" /* retry if lock already taken */ |
---|
44 | "li $3, 1 \n" /* $3 <= argument for sc */ |
---|
45 | "sc $3, 0(%0) \n" /* try to get lock */ |
---|
46 | "bnez $3, lock_ok \n" /* exit if atomic */ |
---|
47 | "lock_delay: \n" |
---|
48 | "li $4, 100 \n" /* $4 <= delay */ |
---|
49 | "lock_loop: \n" |
---|
50 | "addi $4, $4, -1 \n" /* $4 <= $4 - 1 */ |
---|
51 | "beqz $4, lock_loop \n" /* test end delay */ |
---|
52 | "nop \n" |
---|
53 | "j lock_try \n" /* retry if not atomic */ |
---|
54 | "nop \n" |
---|
55 | "lock_ok: \n" |
---|
56 | : |
---|
57 | :"r"(lock) |
---|
58 | :"$2", "$3", "$4"); |
---|
59 | } |
---|
60 | |
---|
61 | ////////////////////////////////////////////////////////////////////////////// |
---|
62 | // mwmr_write() |
---|
63 | // This blocking function returns only when the transfer is completed. |
---|
64 | // It takes the lock for exclusive access before testing the channel state. |
---|
65 | // If there is not enough space in mwmr channel to write nwords words, |
---|
66 | // it writes as many words as possible, release the lock, and retry after |
---|
67 | // a random delay. |
---|
68 | ////////////////////////////////////////////////////////////////////////////// |
---|
69 | void mwmr_write( mwmr_channel_t* mwmr, |
---|
70 | unsigned int* buffer, |
---|
71 | unsigned int nwords ) |
---|
72 | { |
---|
73 | unsigned int x; |
---|
74 | unsigned int spaces; |
---|
75 | |
---|
76 | while(1) |
---|
77 | { |
---|
78 | // get the lock |
---|
79 | mwmr_lock_acquire((unsigned int*)&mwmr->lock); |
---|
80 | |
---|
81 | // compute number of empty slots |
---|
82 | spaces = mwmr->depth - mwmr->sts; |
---|
83 | |
---|
84 | if( spaces >= nwords ) // write nwords, release lock and return |
---|
85 | { |
---|
86 | for ( x = 0 ; x < nwords ; x++ ) |
---|
87 | { |
---|
88 | mwmr->data[mwmr->ptw] = buffer[x]; |
---|
89 | mwmr->ptw = (mwmr->ptw + 1) % mwmr->depth; |
---|
90 | } |
---|
91 | mwmr->sts = mwmr->sts + nwords; |
---|
92 | mwmr->lock = 0; |
---|
93 | return; |
---|
94 | } |
---|
95 | else if ( spaces == 0 ) // release lock and retry after delay |
---|
96 | { |
---|
97 | mwmr->lock = 0; |
---|
98 | for ( x = rand()>>8 ; x > 0 ; x-- ) asm volatile ( "nop" ); |
---|
99 | } |
---|
100 | else // write spaces, release lock and retry after delay |
---|
101 | { |
---|
102 | for ( x = 0 ; x < spaces ; x++ ) |
---|
103 | { |
---|
104 | mwmr->data[mwmr->ptw] = buffer[x]; |
---|
105 | mwmr->ptw = (mwmr->ptw + 1) % mwmr->depth; |
---|
106 | } |
---|
107 | mwmr->sts = mwmr->depth; |
---|
108 | nwords = nwords - spaces; |
---|
109 | buffer = buffer + spaces; |
---|
110 | mwmr->lock = 0; |
---|
111 | } |
---|
112 | |
---|
113 | // random delay before retry |
---|
114 | for ( x = rand()>>6 ; x > 0 ; x-- ) asm volatile ( "nop" ); |
---|
115 | } |
---|
116 | } |
---|
117 | |
---|
118 | ////////////////////////////////////////////////////////////////////////////// |
---|
119 | // mwmr_read() |
---|
120 | // This blocking function returns only when the transfer is completed. |
---|
121 | // It takes the lock for exclusive access before testing the channel state. |
---|
122 | // If there is not enough data in mwmr channel to read nwords words, |
---|
123 | // it reads as many words as possible, release the lock, and retry after |
---|
124 | // a random delay. |
---|
125 | ////////////////////////////////////////////////////////////////////////////// |
---|
126 | void mwmr_read( mwmr_channel_t* mwmr, |
---|
127 | unsigned int* buffer, |
---|
128 | unsigned int nwords ) |
---|
129 | { |
---|
130 | unsigned int x; |
---|
131 | unsigned int dispos; |
---|
132 | |
---|
133 | while(1) |
---|
134 | { |
---|
135 | // get the lock |
---|
136 | mwmr_lock_acquire((unsigned int*)&mwmr->lock); |
---|
137 | |
---|
138 | // compute number of available words |
---|
139 | dispos = mwmr->sts; |
---|
140 | |
---|
141 | if( dispos >= nwords ) // read nwords, release lock and return |
---|
142 | { |
---|
143 | for ( x = 0 ; x < nwords ; x++ ) |
---|
144 | { |
---|
145 | buffer[x] = mwmr->data[mwmr->ptr]; |
---|
146 | mwmr->ptr = (mwmr->ptr + 1) % mwmr->depth; |
---|
147 | } |
---|
148 | mwmr->sts = mwmr->sts - nwords; |
---|
149 | mwmr->lock = 0; |
---|
150 | return; |
---|
151 | } |
---|
152 | else if ( dispos == 0 ) // release lock and retry after delay |
---|
153 | { |
---|
154 | mwmr->lock = 0; |
---|
155 | for ( x = rand()>>8 ; x > 0 ; x-- ) asm volatile ( "nop" ); |
---|
156 | } |
---|
157 | else // read dispos, release lock and retry after delay |
---|
158 | { |
---|
159 | for ( x = 0 ; x < dispos ; x++ ) |
---|
160 | { |
---|
161 | buffer[x] = mwmr->data[mwmr->ptr]; |
---|
162 | mwmr->ptr = (mwmr->ptr + 1) % mwmr->depth; |
---|
163 | } |
---|
164 | mwmr->sts = 0; |
---|
165 | nwords = nwords - dispos; |
---|
166 | buffer = buffer + dispos; |
---|
167 | mwmr->lock = 0; |
---|
168 | } |
---|
169 | |
---|
170 | // random delay before retry |
---|
171 | for ( x = rand()>>6 ; x > 0 ; x-- ) asm volatile ( "nop" ); |
---|
172 | } |
---|
173 | } |
---|
174 | |
---|