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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */
25 #include "gdb_string.h"
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 CORE_ADDR 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
152 dcache_poke_byte
PARAMS ((DCACHE
*dcache
, CORE_ADDR addr
, char *ptr
));
155 dcache_peek_byte
PARAMS ((DCACHE
*dcache
, CORE_ADDR addr
, char *ptr
));
157 static struct dcache_block
*
158 dcache_hit
PARAMS ((DCACHE
*dcache
, CORE_ADDR addr
));
160 static int dcache_write_line
PARAMS ((DCACHE
*dcache
,struct dcache_block
*db
));
162 static struct dcache_block
*dcache_alloc
PARAMS ((DCACHE
*dcache
));
164 static int dcache_writeback
PARAMS ((DCACHE
*dcache
));
166 static void dcache_info
PARAMS ((char *exp
, int tty
));
168 int remote_dcache
= 0;
170 DCACHE
*last_cache
; /* Used by info dcache */
174 /* Free all the data cache blocks, thus discarding all cached data. */
177 dcache_flush (dcache
)
181 dcache
->valid_head
= 0;
182 dcache
->valid_tail
= 0;
184 dcache
->free_head
= 0;
185 dcache
->free_tail
= 0;
187 for (i
= 0; i
< DCACHE_SIZE
; i
++)
189 struct dcache_block
*db
= dcache
->the_cache
+ i
;
191 if (!dcache
->free_head
)
192 dcache
->free_head
= db
;
194 dcache
->free_tail
->p
= db
;
195 dcache
->free_tail
= db
;
199 dcache
->cache_has_stuff
= 0;
204 /* If addr is present in the dcache, return the address of the block
207 static struct dcache_block
*
208 dcache_hit (dcache
, addr
)
212 register struct dcache_block
*db
;
214 /* Search all cache blocks for one that is at this address. */
215 db
= dcache
->valid_head
;
219 if (MASK(addr
) == db
->addr
)
230 /* Make sure that anything in this line which needs to
234 dcache_write_line (dcache
, db
)
236 register struct dcache_block
*db
;
243 for (s
= 0; s
< LINE_SIZE
; s
++)
245 if (db
->state
[s
] == ENTRY_DIRTY
)
248 for (e
= s
; e
< LINE_SIZE
; e
++, len
++)
249 if (db
->state
[e
] != ENTRY_DIRTY
)
252 /* all bytes from s..s+len-1 need to
256 int t
= dcache
->write_memory (db
->addr
+ s
+ done
,
263 memset (db
->state
+ s
, ENTRY_OK
, len
);
274 /* Get a free cache block, put or keep it on the valid list,
275 and return its address. The caller should store into the block
276 the address and data that it describes, then remque it from the
277 free list and insert it into the valid list. This procedure
278 prevents errors from creeping in if a memory retrieval is
279 interrupted (which used to put garbage blocks in the valid
282 static struct dcache_block
*
283 dcache_alloc (dcache
)
286 register struct dcache_block
*db
;
288 if (remote_dcache
== 0)
291 /* Take something from the free list */
292 db
= dcache
->free_head
;
295 dcache
->free_head
= db
->p
;
299 /* Nothing left on free list, so grab one from the valid list */
300 db
= dcache
->valid_head
;
301 dcache
->valid_head
= db
->p
;
303 dcache_write_line (dcache
, db
);
306 /* append this line to end of valid list */
307 if (!dcache
->valid_head
)
308 dcache
->valid_head
= db
;
310 dcache
->valid_tail
->p
= db
;
311 dcache
->valid_tail
= db
;
317 /* Using the data cache DCACHE return the contents of the byte at
318 address ADDR in the remote machine.
320 Returns 0 on error. */
323 dcache_peek_byte (dcache
, addr
, ptr
)
328 register struct dcache_block
*db
= dcache_hit (dcache
, addr
);
332 || db
->state
[XFORM (addr
)] == ENTRY_BAD
)
336 dcache_write_line (dcache
, db
);
339 db
= dcache_alloc (dcache
);
341 db
->addr
= MASK (addr
);
342 while (done
< LINE_SIZE
)
345 (*dcache
->read_memory
)
355 memset (db
->state
, ENTRY_OK
, sizeof (db
->data
));
358 *ptr
= db
->data
[XFORM (addr
)];
362 /* Writeback any dirty lines to the remote. */
364 dcache_writeback (dcache
)
367 struct dcache_block
*db
;
369 db
= dcache
->valid_head
;
373 if (!dcache_write_line (dcache
, db
))
381 /* Using the data cache DCACHE return the contents of the word at
382 address ADDR in the remote machine. */
384 dcache_fetch (dcache
, addr
)
390 if (dcache_xfer_memory (dcache
, addr
, (char *)&res
, sizeof res
, 0) != sizeof res
)
391 memory_error (EIO
, addr
);
397 /* Write the byte at PTR into ADDR in the data cache.
398 Return zero on write error.
402 dcache_poke_byte (dcache
, addr
, ptr
)
407 register struct dcache_block
*db
= dcache_hit (dcache
, addr
);
411 db
= dcache_alloc (dcache
);
412 db
->addr
= MASK (addr
);
413 memset (db
->state
, ENTRY_BAD
, sizeof (db
->data
));
416 db
->data
[XFORM (addr
)] = *ptr
;
417 db
->state
[XFORM (addr
)] = ENTRY_DIRTY
;
422 /* Write the word at ADDR both in the data cache and in the remote machine.
423 Return zero on write error.
427 dcache_poke (dcache
, addr
, data
)
432 if (dcache_xfer_memory (dcache
, addr
, (char *)&data
, sizeof data
, 1) != sizeof data
)
435 return dcache_writeback (dcache
);
439 /* Initialize the data cache. */
441 dcache_init (reading
, writing
)
445 int csize
= sizeof (struct dcache_block
) * DCACHE_SIZE
;
448 dcache
= (DCACHE
*) xmalloc (sizeof (*dcache
));
449 dcache
->read_memory
= reading
;
450 dcache
->write_memory
= writing
;
452 dcache
->the_cache
= (struct dcache_block
*) xmalloc (csize
);
453 memset (dcache
->the_cache
, 0, csize
);
455 dcache_flush (dcache
);
461 /* Read or write LEN bytes from inferior memory at MEMADDR, transferring
462 to or from debugger address MYADDR. Write to inferior if SHOULD_WRITE is
465 Returns length of data written or read; 0 for error.
467 This routine is indended to be called by remote_xfer_ functions. */
470 dcache_xfer_memory (dcache
, memaddr
, myaddr
, len
, should_write
)
481 int (*xfunc
) PARAMS ((DCACHE
*dcache
, CORE_ADDR addr
, char *ptr
));
482 xfunc
= should_write
? dcache_poke_byte
: dcache_peek_byte
;
484 for (i
= 0; i
< len
; i
++)
486 if (!xfunc (dcache
, memaddr
+ i
, myaddr
+ i
))
489 dcache
->cache_has_stuff
= 1;
490 dcache_writeback (dcache
);
495 xfunc
= should_write
? dcache
->write_memory
: dcache
->read_memory
;
497 if (dcache
->cache_has_stuff
)
498 dcache_flush (dcache
);
500 len
= xfunc (memaddr
, myaddr
, len
);
506 dcache_info (exp
, tty
)
510 struct dcache_block
*p
;
514 printf_filtered ("Dcache not enabled\n");
517 printf_filtered ("Dcache enabled, line width %d, depth %d\n",
518 LINE_SIZE
, DCACHE_SIZE
);
520 printf_filtered ("Cache state:\n");
522 for (p
= last_cache
->valid_head
; p
; p
= p
->p
)
525 printf_filtered ("Line at %08xd, referenced %d times\n",
528 for (j
= 0; j
< LINE_SIZE
; j
++)
529 printf_filtered ("%02x", p
->data
[j
] & 0xFF);
530 printf_filtered ("\n");
532 for (j
= 0; j
< LINE_SIZE
; j
++)
533 printf_filtered (" %2x", p
->state
[j
]);
534 printf_filtered ("\n");
539 _initialize_dcache ()
542 (add_set_cmd ("remotecache", class_support
, var_boolean
,
543 (char *) &remote_dcache
,
545 Set cache use for remote targets.\n\
546 When on, use data caching for remote targets. For many remote targets\n\
547 this option can offer better throughput for reading target memory.\n\
548 Unfortunately, gdb does not currently know anything about volatile\n\
549 registers and thus data caching will produce incorrect results with\n\
550 volatile registers are in use. By default, this option is on.",
554 add_info ("dcache", dcache_info
,
555 "Print information on the dcache performance.");
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