1 /* Caching code. Typically used by remote back ends for
4 Copyright 1992, 1993, 1995, 1998 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,
21 Boston, MA 02111-1307, USA. */
26 #include "gdb_string.h"
30 The data cache could lead to incorrect results because it doesn't know
31 about volatile variables, thus making it impossible to debug
32 functions which use memory mapped I/O devices.
38 In general the dcache speeds up performance, some speed improvement
39 comes from the actual caching mechanism, but the major gain is in
40 the reduction of the remote protocol overhead; instead of reading
41 or writing a large area of memory in 4 byte requests, the cache
42 bundles up the requests into 32 byte (actually LINE_SIZE) chunks.
43 Reducing the overhead to an eighth of what it was. This is very
44 obvious when displaying a large amount of data,
49 ----------------------------
50 first time | 4 sec 2 sec improvement due to chunking
51 second time | 4 sec 0 sec improvement due to caching
53 The cache structure is unusual, we keep a number of cache blocks
54 (DCACHE_SIZE) and each one caches a LINE_SIZEed area of memory.
55 Within each line we remember the address of the line (always a
56 multiple of the LINE_SIZE) and a vector of bytes over the range.
57 There's another vector which contains the state of the bytes.
59 ENTRY_BAD means that the byte is just plain wrong, and has no
60 correspondence with anything else (as it would when the cache is
61 turned on, but nothing has been done to it.
63 ENTRY_DIRTY means that the byte has some data in it which should be
64 written out to the remote target one day, but contains correct
65 data. ENTRY_OK means that the data is the same in the cache as it
69 The ENTRY_DIRTY state is necessary because GDB likes to write large
70 lumps of memory in small bits. If the caching mechanism didn't
71 maintain the DIRTY information, then something like a two byte
72 write would mean that the entire cache line would have to be read,
73 the two bytes modified and then written out again. The alternative
74 would be to not read in the cache line in the first place, and just
75 write the two bytes directly into target memory. The trouble with
76 that is that it really nails performance, because of the remote
77 protocol overhead. This way, all those little writes are bundled
78 up into an entire cache line write in one go, without having to
79 read the cache line in the first place.
85 /* This value regulates the number of cache blocks stored.
86 Smaller values reduce the time spent searching for a cache
87 line, and reduce memory requirements, but increase the risk
88 of a line not being in memory */
90 #define DCACHE_SIZE 64
92 /* This value regulates the size of a cache line. Smaller values
93 reduce the time taken to read a single byte, but reduce overall
96 #define LINE_SIZE_POWER (5)
97 #define LINE_SIZE (1 << LINE_SIZE_POWER)
99 /* Each cache block holds LINE_SIZE bytes of data
100 starting at a multiple-of-LINE_SIZE address. */
102 #define LINE_SIZE_MASK ((LINE_SIZE - 1))
103 #define XFORM(x) ((x) & LINE_SIZE_MASK)
104 #define MASK(x) ((x) & ~LINE_SIZE_MASK)
107 #define ENTRY_BAD 0 /* data at this byte is wrong */
108 #define ENTRY_DIRTY 1 /* data at this byte needs to be written back */
109 #define ENTRY_OK 2 /* data at this byte is same as in memory */
114 struct dcache_block *p; /* next in list */
115 CORE_ADDR addr; /* Address for which data is recorded. */
116 char data[LINE_SIZE]; /* bytes at given address */
117 unsigned char state[LINE_SIZE]; /* what state the data is in */
119 /* whether anything in state is dirty - used to speed up the
129 /* Function to actually read the target memory. */
130 memxferfunc read_memory;
132 /* Function to actually write the target memory */
133 memxferfunc write_memory;
136 struct dcache_block *free_head;
137 struct dcache_block *free_tail;
140 struct dcache_block *valid_head;
141 struct dcache_block *valid_tail;
143 /* The cache itself. */
144 struct dcache_block *the_cache;
146 /* potentially, if the cache was enabled, and then turned off, and
147 then turned on again, the stuff in it could be stale, so this is
152 static int dcache_poke_byte PARAMS ((DCACHE * dcache, CORE_ADDR addr,
155 static int dcache_peek_byte PARAMS ((DCACHE * dcache, CORE_ADDR addr,
158 static struct dcache_block *dcache_hit PARAMS ((DCACHE * dcache,
161 static int dcache_write_line PARAMS ((DCACHE * dcache, struct dcache_block * db));
163 static struct dcache_block *dcache_alloc PARAMS ((DCACHE * dcache));
165 static int dcache_writeback PARAMS ((DCACHE * dcache));
167 static void dcache_info PARAMS ((char *exp, int tty));
169 void _initialize_dcache PARAMS ((void));
171 int remote_dcache = 0;
173 DCACHE *last_cache; /* Used by info dcache */
176 /* Free all the data cache blocks, thus discarding all cached data. */
179 dcache_flush (dcache)
183 dcache->valid_head = 0;
184 dcache->valid_tail = 0;
186 dcache->free_head = 0;
187 dcache->free_tail = 0;
189 for (i = 0; i < DCACHE_SIZE; i++)
191 struct dcache_block *db = dcache->the_cache + i;
193 if (!dcache->free_head)
194 dcache->free_head = db;
196 dcache->free_tail->p = db;
197 dcache->free_tail = db;
201 dcache->cache_has_stuff = 0;
206 /* If addr is present in the dcache, return the address of the block
209 static struct dcache_block *
210 dcache_hit (dcache, addr)
214 register struct dcache_block *db;
216 /* Search all cache blocks for one that is at this address. */
217 db = dcache->valid_head;
221 if (MASK (addr) == db->addr)
232 /* Make sure that anything in this line which needs to
236 dcache_write_line (dcache, db)
238 register struct dcache_block *db;
245 for (s = 0; s < LINE_SIZE; s++)
247 if (db->state[s] == ENTRY_DIRTY)
250 for (e = s; e < LINE_SIZE; e++, len++)
251 if (db->state[e] != ENTRY_DIRTY)
254 /* all bytes from s..s+len-1 need to
259 int t = dcache->write_memory (db->addr + s + done,
266 memset (db->state + s, ENTRY_OK, len);
277 /* Get a free cache block, put or keep it on the valid list,
278 and return its address. The caller should store into the block
279 the address and data that it describes, then remque it from the
280 free list and insert it into the valid list. This procedure
281 prevents errors from creeping in if a memory retrieval is
282 interrupted (which used to put garbage blocks in the valid
285 static struct dcache_block *
286 dcache_alloc (dcache)
289 register struct dcache_block *db;
291 if (remote_dcache == 0)
294 /* Take something from the free list */
295 db = dcache->free_head;
298 dcache->free_head = db->p;
302 /* Nothing left on free list, so grab one from the valid list */
303 db = dcache->valid_head;
304 dcache->valid_head = db->p;
306 dcache_write_line (dcache, db);
309 /* append this line to end of valid list */
310 if (!dcache->valid_head)
311 dcache->valid_head = db;
313 dcache->valid_tail->p = db;
314 dcache->valid_tail = db;
320 /* Using the data cache DCACHE return the contents of the byte at
321 address ADDR in the remote machine.
323 Returns 0 on error. */
326 dcache_peek_byte (dcache, addr, ptr)
331 register struct dcache_block *db = dcache_hit (dcache, addr);
335 || db->state[XFORM (addr)] == ENTRY_BAD)
339 dcache_write_line (dcache, db);
342 db = dcache_alloc (dcache);
344 db->addr = MASK (addr);
345 while (done < LINE_SIZE)
348 (*dcache->read_memory)
358 memset (db->state, ENTRY_OK, sizeof (db->data));
361 *ptr = db->data[XFORM (addr)];
365 /* Writeback any dirty lines to the remote. */
367 dcache_writeback (dcache)
370 struct dcache_block *db;
372 db = dcache->valid_head;
376 if (!dcache_write_line (dcache, db))
384 /* Using the data cache DCACHE return the contents of the word at
385 address ADDR in the remote machine. */
387 dcache_fetch (dcache, addr)
393 if (dcache_xfer_memory (dcache, addr, (char *) &res, sizeof res, 0) != sizeof res)
394 memory_error (EIO, addr);
400 /* Write the byte at PTR into ADDR in the data cache.
401 Return zero on write error.
405 dcache_poke_byte (dcache, addr, ptr)
410 register struct dcache_block *db = dcache_hit (dcache, addr);
414 db = dcache_alloc (dcache);
415 db->addr = MASK (addr);
416 memset (db->state, ENTRY_BAD, sizeof (db->data));
419 db->data[XFORM (addr)] = *ptr;
420 db->state[XFORM (addr)] = ENTRY_DIRTY;
425 /* Write the word at ADDR both in the data cache and in the remote machine.
426 Return zero on write error.
430 dcache_poke (dcache, addr, data)
435 if (dcache_xfer_memory (dcache, addr, (char *) &data, sizeof data, 1) != sizeof data)
438 return dcache_writeback (dcache);
442 /* Initialize the data cache. */
444 dcache_init (reading, writing)
448 int csize = sizeof (struct dcache_block) * DCACHE_SIZE;
451 dcache = (DCACHE *) xmalloc (sizeof (*dcache));
452 dcache->read_memory = reading;
453 dcache->write_memory = writing;
455 dcache->the_cache = (struct dcache_block *) xmalloc (csize);
456 memset (dcache->the_cache, 0, csize);
458 dcache_flush (dcache);
464 /* Read or write LEN bytes from inferior memory at MEMADDR, transferring
465 to or from debugger address MYADDR. Write to inferior if SHOULD_WRITE is
468 Returns length of data written or read; 0 for error.
470 This routine is indended to be called by remote_xfer_ functions. */
473 dcache_xfer_memory (dcache, memaddr, myaddr, len, should_write)
484 int (*xfunc) PARAMS ((DCACHE * dcache, CORE_ADDR addr, char *ptr));
485 xfunc = should_write ? dcache_poke_byte : dcache_peek_byte;
487 for (i = 0; i < len; i++)
489 if (!xfunc (dcache, memaddr + i, myaddr + i))
492 dcache->cache_has_stuff = 1;
493 dcache_writeback (dcache);
498 xfunc = should_write ? dcache->write_memory : dcache->read_memory;
500 if (dcache->cache_has_stuff)
501 dcache_flush (dcache);
503 len = xfunc (memaddr, myaddr, len);
509 dcache_info (exp, tty)
513 struct dcache_block *p;
517 printf_filtered ("Dcache not enabled\n");
520 printf_filtered ("Dcache enabled, line width %d, depth %d\n",
521 LINE_SIZE, DCACHE_SIZE);
523 printf_filtered ("Cache state:\n");
525 for (p = last_cache->valid_head; p; p = p->p)
528 printf_filtered ("Line at %08xd, referenced %d times\n",
531 for (j = 0; j < LINE_SIZE; j++)
532 printf_filtered ("%02x", p->data[j] & 0xFF);
533 printf_filtered ("\n");
535 for (j = 0; j < LINE_SIZE; j++)
536 printf_filtered (" %2x", p->state[j]);
537 printf_filtered ("\n");
542 _initialize_dcache ()
545 (add_set_cmd ("remotecache", class_support, var_boolean,
546 (char *) &remote_dcache,
548 Set cache use for remote targets.\n\
549 When on, use data caching for remote targets. For many remote targets\n\
550 this option can offer better throughput for reading target memory.\n\
551 Unfortunately, gdb does not currently know anything about volatile\n\
552 registers and thus data caching will produce incorrect results with\n\
553 volatile registers are in use. By default, this option is on.",
557 add_info ("dcache", dcache_info,
558 "Print information on the dcache performance.");