git.sur5r.net Git - cc65/blob - src/sim65/memory.c

   1 /*****************************************************************************/
   2 /*                                                                           */
   3 /*                                 memory.h                                  */
   4 /*                                                                           */
   5 /*                  Memory subsystem for the 6502 simulator                  */
   6 /*                                                                           */
   7 /*                                                                           */
   8 /*                                                                           */
   9 /* (C) 2002-2012, Ullrich von Bassewitz                                      */
  10 /*                Roemerstrasse 52                                           */
  11 /*                D-70794 Filderstadt                                        */
  12 /* EMail:         uz@cc65.org                                                */
  13 /*                                                                           */
  14 /*                                                                           */
  15 /* This software is provided 'as-is', without any expressed or implied       */
  16 /* warranty.  In no event will the authors be held liable for any damages    */
  17 /* arising from the use of this software.                                    */
  18 /*                                                                           */
  19 /* Permission is granted to anyone to use this software for any purpose,     */
  20 /* including commercial applications, and to alter it and redistribute it    */
  21 /* freely, subject to the following restrictions:                            */
  22 /*                                                                           */
  23 /* 1. The origin of this software must not be misrepresented; you must not   */
  24 /*    claim that you wrote the original software. If you use this software   */
  25 /*    in a product, an acknowledgment in the product documentation would be  */
  26 /*    appreciated but is not required.                                       */
  27 /* 2. Altered source versions must be plainly marked as such, and must not   */
  28 /*    be misrepresented as being the original software.                      */
  29 /* 3. This notice may not be removed or altered from any source              */
  30 /*    distribution.                                                          */
  31 /*                                                                           */
  32 /*****************************************************************************/
  33
  34
  35
  36 #include <string.h>
  37
  38 #include "memory.h"
  39
  40
  41
  42 /*****************************************************************************/
  43 /*                                   Data                                    */
  44 /*****************************************************************************/
  45
  46
  47
  48 /* THE memory */
  49 static unsigned char Mem[0x10000];
  50
  51
  52
  53 /*****************************************************************************/
  54 /*                                   Code                                    */
  55 /*****************************************************************************/
  56
  57
  58
  59 void MemWriteByte (unsigned Addr, unsigned char Val)
  60 /* Write a byte to a memory location */
  61 {
  62     Mem[Addr] = Val;
  63 }
  64
  65
  66
  67 unsigned char MemReadByte (unsigned Addr)
  68 /* Read a byte from a memory location */
  69 {
  70     return Mem[Addr];
  71 }
  72
  73
  74
  75 unsigned MemReadWord (unsigned Addr)
  76 /* Read a word from a memory location */
  77 {
  78     unsigned W = MemReadByte (Addr++);
  79     return (W | (MemReadByte (Addr) << 8));
  80 }
  81
  82
  83
  84 unsigned MemReadZPWord (unsigned char Addr)
  85 /* Read a word from the zero page. This function differs from ReadMemW in that
  86 ** the read will always be in the zero page, even in case of an address
  87 ** overflow.
  88 */
  89 {
  90     unsigned W = MemReadByte (Addr++);
  91     return (W | (MemReadByte (Addr) << 8));
  92 }
  93
  94
  95
  96 void MemInit (void)
  97 /* Initialize the memory subsystem */
  98 {
  99     /* Fill momory with illegal opcode */
 100     memset (Mem, 0xFF, sizeof (Mem));
 101
 102     /* Set RESET vector to 0x0200 */
 103     Mem[0xFFFC] = 0x00;
 104     Mem[0xFFFD] = 0x02;
 105 }