1 /* Caching code. Typically used by remote back ends for
4 Copyright 1992, 1993, 1995 Free Software Foundation, Inc.
6 This file is part of GDB.
8 This program is free software; you can redistribute it and/or modify
9 it under the terms of the GNU General Public License as published by
10 the Free Software Foundation; either version 2 of the License, or
11 (at your option) any later version.
13 This program is distributed in the hope that it will be useful,
14 but WITHOUT ANY WARRANTY; without even the implied warranty of
15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 GNU General Public License for more details.
18 You should have received a copy of the GNU General Public License
19 along with this program; if not, write to the Free Software
20 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */
29 The data cache could lead to incorrect results because it doesn't know
30 about volatile variables, thus making it impossible to debug
31 functions which use memory mapped I/O devices.
37 In general the dcache speeds up performance, some speed improvement
38 comes from the actual caching mechanism, but the major gain is in
39 the reduction of the remote protocol overhead; instead of reading
40 or writing a large area of memory in 4 byte requests, the cache
41 bundles up the requests into 32 byte (actually LINE_SIZE) chunks.
42 Reducing the overhead to an eighth of what it was. This is very
43 obvious when displaying a large amount of data,
48 ----------------------------
49 first time | 4 sec 2 sec improvement due to chunking
50 second time | 4 sec 0 sec improvement due to caching
52 The cache structure is unusual, we keep a number of cache blocks
53 (DCACHE_SIZE) and each one caches a LINE_SIZEed area of memory.
54 Within each line we remember the address of the line (always a
55 multiple of the LINE_SIZE) and a vector of bytes over the range.
56 There's another vector which contains the state of the bytes.
58 ENTRY_BAD means that the byte is just plain wrong, and has no
59 correspondence with anything else (as it would when the cache is
60 turned on, but nothing has been done to it.
62 ENTRY_DIRTY means that the byte has some data in it which should be
63 written out to the remote target one day, but contains correct
64 data. ENTRY_OK means that the data is the same in the cache as it
68 The ENTRY_DIRTY state is necessary because GDB likes to write large
69 lumps of memory in small bits. If the caching mechanism didn't
70 maintain the DIRTY information, then something like a two byte
71 write would mean that the entire cache line would have to be read,
72 the two bytes modified and then written out again. The alternative
73 would be to not read in the cache line in the first place, and just
74 write the two bytes directly into target memory. The trouble with
75 that is that it really nails performance, because of the remote
76 protocol overhead. This way, all those little writes are bundled
77 up into an entire cache line write in one go, without having to
78 read the cache line in the first place.
84 /* This value regulates the number of cache blocks stored.
85 Smaller values reduce the time spent searching for a cache
86 line, and reduce memory requirements, but increase the risk
87 of a line not being in memory */
89 #define DCACHE_SIZE 64
91 /* This value regulates the size of a cache line. Smaller values
92 reduce the time taken to read a single byte, but reduce overall
95 #define LINE_SIZE_POWER (5)
96 #define LINE_SIZE (1 << LINE_SIZE_POWER)
98 /* Each cache block holds LINE_SIZE bytes of data
99 starting at a multiple-of-LINE_SIZE address. */
101 #define LINE_SIZE_MASK ((LINE_SIZE - 1))
102 #define XFORM(x) ((x) & LINE_SIZE_MASK)
103 #define MASK(x) ((x) & ~LINE_SIZE_MASK)
106 #define ENTRY_BAD 0 /* data at this byte is wrong */
107 #define ENTRY_DIRTY 1 /* data at this byte needs to be written back */
108 #define ENTRY_OK 2 /* data at this byte is same as in memory */
113 struct dcache_block
*p
; /* next in list */
114 unsigned int addr
; /* Address for which data is recorded. */
115 char data
[LINE_SIZE
]; /* bytes at given address */
116 unsigned char state
[LINE_SIZE
]; /* what state the data is in */
118 /* whether anything in state is dirty - used to speed up the
128 /* Function to actually read the target memory. */
129 memxferfunc read_memory
;
131 /* Function to actually write the target memory */
132 memxferfunc write_memory
;
135 struct dcache_block
*free_head
;
136 struct dcache_block
*free_tail
;
139 struct dcache_block
*valid_head
;
140 struct dcache_block
*valid_tail
;
142 /* The cache itself. */
143 struct dcache_block
*the_cache
;
145 /* potentially, if the cache was enabled, and then turned off, and
146 then turned on again, the stuff in it could be stale, so this is
151 int remote_dcache
= 1;
153 DCACHE
*last_cache
; /* Used by info dcache */
157 /* Free all the data cache blocks, thus discarding all cached data. */
160 dcache_flush (dcache
)
164 dcache
->valid_head
= 0;
165 dcache
->valid_tail
= 0;
167 dcache
->free_head
= 0;
168 dcache
->free_tail
= 0;
170 for (i
= 0; i
< DCACHE_SIZE
; i
++)
172 struct dcache_block
*db
= dcache
->the_cache
+ i
;
174 if (!dcache
->free_head
)
175 dcache
->free_head
= db
;
177 dcache
->free_tail
->p
= db
;
178 dcache
->free_tail
= db
;
182 dcache
->cache_has_stuff
= 0;
187 /* If addr is present in the dcache, return the address of the block
190 struct dcache_block
*
191 dcache_hit (dcache
, addr
)
195 register struct dcache_block
*db
;
197 /* Search all cache blocks for one that is at this address. */
198 db
= dcache
->valid_head
;
202 if (MASK(addr
) == db
->addr
)
213 /* Make sure that anything in this line which needs to
217 dcache_write_line (dcache
, db
)
219 register struct dcache_block
*db
;
226 for (s
= 0; s
< LINE_SIZE
; s
++)
228 if (db
->state
[s
] == ENTRY_DIRTY
)
231 for (e
= s
; e
< LINE_SIZE
; e
++, len
++)
232 if (db
->state
[e
] != ENTRY_DIRTY
)
234 /* all bytes from s..s+len-1 need to
238 int t
= dcache
->write_memory (db
->addr
+ s
+ done
,
245 memset (db
->state
+ s
, ENTRY_OK
, len
);
257 /* Get a free cache block, put or keep it on the valid list,
258 and return its address. The caller should store into the block
259 the address and data that it describes, then remque it from the
260 free list and insert it into the valid list. This procedure
261 prevents errors from creeping in if a memory retrieval is
262 interrupted (which used to put garbage blocks in the valid
265 struct dcache_block
*
266 dcache_alloc (dcache
)
269 register struct dcache_block
*db
;
271 if (remote_dcache
== 0)
274 /* Take something from the free list */
275 db
= dcache
->free_head
;
278 dcache
->free_head
= db
->p
;
282 /* Nothing left on free list, so grab one from the valid list */
283 db
= dcache
->valid_head
;
284 dcache
->valid_head
= db
->p
;
286 dcache_write_line (dcache
, db
);
289 /* append this line to end of valid list */
290 if (!dcache
->valid_head
)
291 dcache
->valid_head
= db
;
293 dcache
->valid_tail
->p
= db
;
294 dcache
->valid_tail
= db
;
300 /* Using the data cache DCACHE return the contents of the byte at
301 address ADDR in the remote machine.
303 Returns 0 on error. */
306 dcache_peek_byte (dcache
, addr
, ptr
)
311 register struct dcache_block
*db
= dcache_hit (dcache
, addr
);
315 || db
->state
[XFORM (addr
)] == ENTRY_BAD
)
319 dcache_write_line (dcache
, db
);
322 db
= dcache_alloc (dcache
);
324 db
->addr
= MASK (addr
);
325 while (done
< LINE_SIZE
)
328 (*dcache
->read_memory
)
338 memset (db
->state
, ENTRY_OK
, sizeof (db
->data
));
341 *ptr
= db
->data
[XFORM (addr
)];
345 /* Using the data cache DCACHE return the contents of the word at
346 address ADDR in the remote machine.
348 Returns 0 on error. */
351 dcache_peek (dcache
, addr
, data
)
356 char *dp
= (char *) data
;
358 for (i
= 0; i
< sizeof (int); i
++)
360 if (!dcache_peek_byte (dcache
, addr
, dp
+ i
))
367 /* Writeback any dirty lines to the remote. */
369 dcache_writeback (dcache
)
372 struct dcache_block
*db
;
374 db
= dcache
->valid_head
;
378 if (!dcache_write_line (dcache
, db
))
386 /* Using the data cache DCACHE return the contents of the word at
387 address ADDR in the remote machine. */
389 dcache_fetch (dcache
, addr
)
394 dcache_peek (dcache
, addr
, &res
);
399 /* Write the byte at PTR into ADDR in the data cache.
400 Return zero on write error.
404 dcache_poke_byte (dcache
, addr
, ptr
)
409 register struct dcache_block
*db
= dcache_hit (dcache
, addr
);
413 db
= dcache_alloc (dcache
);
414 db
->addr
= MASK (addr
);
415 memset (db
->state
, ENTRY_BAD
, sizeof (db
->data
));
418 db
->data
[XFORM (addr
)] = *ptr
;
419 db
->state
[XFORM (addr
)] = ENTRY_DIRTY
;
424 /* Write the word at ADDR both in the data cache and in the remote machine.
425 Return zero on write error.
429 dcache_poke (dcache
, addr
, data
)
434 char *dp
= (char *) (&data
);
436 for (i
= 0; i
< sizeof (int); i
++)
438 if (!dcache_poke_byte (dcache
, addr
, dp
+ i
))
441 dcache_writeback (dcache
);
446 /* Initialize the data cache. */
448 dcache_init (reading
, writing
)
452 int csize
= sizeof (struct dcache_block
) * DCACHE_SIZE
;
455 dcache
= (DCACHE
*) xmalloc (sizeof (*dcache
));
456 dcache
->read_memory
= reading
;
457 dcache
->write_memory
= writing
;
459 dcache
->the_cache
= (struct dcache_block
*) xmalloc (csize
);
460 memset (dcache
->the_cache
, 0, csize
);
462 dcache_flush (dcache
);
468 /* Read or write LEN bytes from inferior memory at MEMADDR, transferring
469 to or from debugger address MYADDR. Write to inferior if SHOULD_WRITE is
472 Returns length of data written or read; 0 for error.
474 This routine is indended to be called by remote_xfer_ functions. */
477 dcache_xfer_memory (dcache
, memaddr
, myaddr
, len
, should_write
)
489 = should_write
? dcache_poke_byte
: dcache_peek_byte
;
491 for (i
= 0; i
< len
; i
++)
493 if (!xfunc (dcache
, memaddr
+ i
, myaddr
+ i
))
496 dcache
->cache_has_stuff
= 1;
497 dcache_writeback (dcache
);
502 = should_write
? dcache
->write_memory
: dcache
->read_memory
;
504 if (dcache
->cache_has_stuff
)
505 dcache_flush (dcache
);
507 len
= xfunc (memaddr
, myaddr
, len
);
513 dcache_info (exp
, tty
)
517 struct dcache_block
*p
;
521 printf_filtered ("Dcache not enabled\n");
524 printf_filtered ("Dcache enabled, line width %d, depth %d\n",
525 LINE_SIZE
, DCACHE_SIZE
);
527 printf_filtered ("Cache state:\n");
529 for (p
= last_cache
->valid_head
; p
; p
= p
->p
)
532 printf_filtered ("Line at %08xd, referenced %d times\n",
535 for (j
= 0; j
< LINE_SIZE
; j
++)
536 printf_filtered ("%02x", p
->data
[j
] & 0xFF);
537 printf_filtered ("\n");
539 for (j
= 0; j
< LINE_SIZE
; j
++)
540 printf_filtered (" %2x", p
->state
[j
]);
541 printf_filtered ("\n");
546 _initialize_dcache ()
549 (add_set_cmd ("remotecache", class_support
, var_boolean
,
550 (char *) &remote_dcache
,
552 Set cache use for remote targets.\n\
553 When on, use data caching for remote targets. For many remote targets\n\
554 this option can offer better throughput for reading target memory.\n\
555 Unfortunately, gdb does not currently know anything about volatile\n\
556 registers and thus data caching will produce incorrect results with\n\
557 volatile registers are in use. By default, this option is on.",
561 add_info ("dcache", dcache_info
,
562 "Print information on the dcache performance.");
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