ticketlock/mem.spin

   1 /*
   2  * This program is free software; you can redistribute it and/or modify
   3  * it under the terms of the GNU General Public License as published by
   4  * the Free Software Foundation; either version 2 of the License, or
   5  * (at your option) any later version.
   6  *
   7  * This program is distributed in the hope that it will be useful,
   8  * but WITHOUT ANY WARRANTY; without even the implied warranty of
   9  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  10  * GNU General Public License for more details.
  11  *
  12  * You should have received a copy of the GNU General Public License
  13  * along with this program; if not, write to the Free Software
  14  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  15  *
  16  * Copyright (c) 2009 Mathieu Desnoyers
  17  */
  18
  19 /* 16 CPUs max (byte has 8 bits, divided in two) */
  20
  21 #ifndef CONFIG_BITS_PER_BYTE
  22 #define BITS_PER_BYTE           8
  23 #else
  24 #define BITS_PER_BYTE           CONFIG_BITS_PER_BYTE
  25 #endif
  26
  27 #define HBPB                    (BITS_PER_BYTE / 2)     /* 4 */
  28 #define HMASK                   ((1 << HBPB) - 1)       /* 0x0F */
  29
  30 /* for byte type */
  31 #define LOW_HALF(val)           ((val) & HMASK)
  32 #define LOW_HALF_INC            1
  33
  34 #define HIGH_HALF(val)          ((val) & (HMASK << HBPB))
  35 #define HIGH_HALF_INC           (1 << HBPB)
  36
  37 byte lock = 0;
  38 byte refcount = 0;
  39
  40 inline spin_lock(lock, ticket)
  41 {
  42         atomic {
  43                 ticket = HIGH_HALF(lock) >> HBPB;
  44                 lock = lock + HIGH_HALF_INC;    /* overflow expected */
  45         }
  46
  47         /* busy-wait */
  48         LOW_HALF(lock) == ticket -> 1;
  49 }
  50
  51 inline spin_unlock(lock)
  52 {
  53         lock = HIGH_HALF(lock) | LOW_HALF(lock + LOW_HALF_INC);
  54 }
  55
  56 proctype proc_X()
  57 {
  58         byte ticket;
  59
  60         do
  61         ::      spin_lock(lock, ticket);
  62                 refcount = refcount + 1;
  63                 refcount = refcount - 1;
  64                 spin_unlock(lock);
  65         od;
  66 }
  67
  68 init
  69 {
  70         run proc_X();
  71         run proc_X();
  72         run proc_X();
  73         run proc_X();
  74         run proc_X();
  75 }