pipesim/cache.h

   1 /*
   2   Copyright (c) 2020 Peter Hsu.  All Rights Reserved.  See LICENCE file for details.
   3 */
   4
   5
   6 #ifndef CACHE_T
   7 #define CACHE_T
   8
   9
  10 struct tag_t {                  /* 16 byte object */
  11   long      addr     ;          /* 64-bit entry */
  12   unsigned dirty :  1;          /*  1 bit flag */
  13   long     ready : 63;          /* 63 bit time */
  14 };
  15
  16 struct lru_fsm_t {
  17   unsigned short way;           /* cache way to look up */
  18   unsigned short next_state;    /* number if hit */
  19 };
  20
  21 struct cache_t {                /* cache descriptor */
  22   struct lru_fsm_t* fsm;        /* LRU state transitions [ways!][ways] */
  23   long line;                    /* line size in bytes */
  24   long rows;                    /* number of rows */
  25   long ways;                    /* number of ways */
  26   long lg_line, lg_rows;                /* specified in log-base-2 units */
  27   long row_mask;                /* row index mask = (1<<lg_rows)-1 */
  28   struct tag_t** tags;          /* cache tag array [ways]->[rows] */
  29   unsigned short* states;       /* LRU state vector [rows] */
  30   long* evicted;                /* tag of evicted line, 0 if clean, NULL if unwritable */
  31   long penalty;                 /* cycles to refill line */
  32   long refs, misses;            /* count number of */
  33   long updates, evictions;      /* if writeable */
  34 };
  35
  36 void flush_cache( struct cache_t* c );
  37
  38 void init_cache( struct cache_t* c, struct lru_fsm_t* fsm, int writeable );
  39
  40 void show_cache( struct cache_t* c );
  41
  42
  43 /* returns cycle when line available (may be in past)
  44      cache miss if return value == when_miss_arrive */
  45 static inline long lookup_cache( struct cache_t* c, long addr, int write, long when_miss_arrive )
  46 {
  47   c->refs++;
  48   addr >>= c->lg_line;          /* make proper tag (ok to include index) */
  49   int index = addr & c->row_mask;
  50   unsigned short* state = c->states + index;
  51
  52   struct lru_fsm_t* p = c->fsm + *state; /* recall c->fsm points to [-1] */
  53   struct lru_fsm_t* end = p + c->ways;   /* hence +ways = last entry */
  54   struct tag_t* tag;
  55   do {
  56     p++;
  57     tag = c->tags[p->way] + index;
  58     if (addr == tag->addr)
  59       goto cache_hit;
  60   } while (p < end);
  61
  62   c->misses++;
  63   if (tag->dirty) {
  64     *c->evicted = tag->addr;    /* will SEGV if not cache not writable */
  65     c->evictions++;             /* can conveniently point to your location */
  66     tag->dirty = 0;
  67   }
  68   else if (c->evicted)
  69     *c->evicted = 0;
  70   tag->addr = addr;
  71   tag->ready = when_miss_arrive;
  72
  73  cache_hit:
  74   *state = p->next_state;       /* already multiplied by c->ways */
  75   if (write) {
  76     tag->dirty = 1;
  77     c->updates++;
  78   }
  79   return tag->ready;
  80 }
  81
  82
  83
  84 #endif