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 */
49static unsigned char Mem[0x10000];
50
51
52
53/*****************************************************************************/
54/* Code */
55/*****************************************************************************/
56
57
58
59void MemWriteByte (unsigned Addr, unsigned char Val)
60/* Write a byte to a memory location */
61{
62 Mem[Addr] = Val;
63}
64
65
66
67void MemWriteWord (unsigned Addr, unsigned Val)
68/* Write a word to a memory location */
69{
70 MemWriteByte (Addr, Val & 0xFF);
71 MemWriteByte (Addr + 1, Val >> 8);
72}
73
74
75
76unsigned char MemReadByte (unsigned Addr)
77/* Read a byte from a memory location */
78{
79 return Mem[Addr];
80}
81
82
83
84unsigned MemReadWord (unsigned Addr)
85/* Read a word from a memory location */
86{
87 unsigned W = MemReadByte (Addr++);
88 return (W | (MemReadByte (Addr) << 8));
89}
90
91
92
93unsigned MemReadZPWord (unsigned char Addr)
94/* Read a word from the zero page. This function differs from MemReadWord in that
95** the read will always be in the zero page, even in case of an address
96** overflow.
97*/
98{
99 unsigned W = MemReadByte (Addr++);
100 return (W | (MemReadByte (Addr) << 8));
101}
102
103
104
105void MemInit (void)
106/* Initialize the memory subsystem */
107{
108 /* Fill memory with illegal opcode */
109 memset (Mem, 0xFF, sizeof (Mem));
110}
111