common/memsize.c

   1 /*
   2  * (C) Copyright 2004
   3  * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
   4  *
   5  * See file CREDITS for list of people who contributed to this
   6  * project.
   7  *
   8  * This program is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU General Public License as
  10  * published by the Free Software Foundation; either version 2 of
  11  * the License, or (at your option) any later version.
  12  *
  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.
  17  *
  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,
  21  * MA 02111-1307 USA
  22  */
  23
  24
  25 /*
  26  * Check memory range for valid RAM. A simple memory test determines
  27  * the actually available RAM size between addresses `base' and
  28  * `base + maxsize'.
  29  */
  30 long get_ram_size(volatile long *base, long maxsize)
  31 {
  32         volatile long *addr;
  33         long           save[32];
  34         long           cnt;
  35         long           val;
  36         long           size;
  37         int            i = 0;
  38
  39         for (cnt = (maxsize / sizeof (long)) >> 1; cnt > 0; cnt >>= 1) {
  40                 addr = base + cnt;      /* pointer arith! */
  41                 save[i++] = *addr;
  42                 *addr = ~cnt;
  43         }
  44
  45         addr = base;
  46         save[i] = *addr;
  47         *addr = 0;
  48
  49         if ((val = *addr) != 0) {
  50                 /* Restore the original data before leaving the function.
  51                  */
  52                 *addr = save[i];
  53                 for (cnt = 1; cnt < maxsize / sizeof(long); cnt <<= 1) {
  54                         addr  = base + cnt;
  55                         *addr = save[--i];
  56                 }
  57                 return (0);
  58         }
  59
  60         for (cnt = 1; cnt < maxsize / sizeof (long); cnt <<= 1) {
  61                 addr = base + cnt;      /* pointer arith! */
  62                 val = *addr;
  63                 *addr = save[--i];
  64                 if (val != ~cnt) {
  65                         size = cnt * sizeof (long);
  66                         /* Restore the original data before leaving the function.
  67                          */
  68                         for (cnt <<= 1; cnt < maxsize / sizeof (long); cnt <<= 1) {
  69                                 addr  = base + cnt;
  70                                 *addr = save[--i];
  71                         }
  72                         return (size);
  73                 }
  74         }
  75
  76         return (maxsize);
  77 }