src/libcpu/execute.c

   1 /* CPU emulation loop and memory access
   2  *
   3  * (C) 2018 by Andreas Eversberg <jolly@eversberg.eu>
   4  * All Rights Reserved
   5  *
   6  * This program is free software: you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation, either version 3 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18  */
  19
  20 #include <stdio.h>
  21 #include <stdint.h>
  22 #include <stdlib.h>
  23 #include "execute.h"
  24 #include "m68k.h"
  25 #include "m68kcpu.h"
  26
  27 //#define DEBUG_CPU
  28
  29 #define IOMASK  0xfffff000
  30 #define IOBASE  0x00dff000
  31
  32 static uint8_t *memory = NULL;
  33 static uint32_t memory_size = 0;
  34 static uint16_t *chipreg = NULL;
  35
  36 static uint16_t read_io(unsigned int address)
  37 {
  38 #ifdef DEBUG_CPU
  39         printf("Chip read from 0x%08x\n", address);
  40 #endif
  41         return emulate_io_read(address);
  42 }
  43
  44 static void write_io(unsigned int address, uint16_t value)
  45 {
  46 #ifdef DEBUG_CPU
  47         printf("Chip write to 0x%08x\n", address);
  48 #endif
  49         if ((address & IOMASK) == IOBASE)
  50                 chipreg[address & ~IOMASK] = value;
  51         emulate_io_write(address, value);
  52 }
  53
  54 unsigned int m68k_read_memory_8(unsigned int address)
  55 {
  56         if (address > memory_size - 1) {
  57                 if ((address & 1)) {
  58                         /* read lower (right) byte */
  59                         return read_io(address & ~1);
  60                 } else {
  61                         /* read upper (left) byte */
  62                         return read_io(address) >> 8;
  63                 }
  64         }
  65         return *((uint8_t *)(memory + address));
  66 }
  67
  68 unsigned int m68k_read_memory_16(unsigned int address)
  69 {
  70         if (address > memory_size - 2) {
  71                 return read_io(address);
  72         }
  73         return  (memory[address] << 8) |
  74                  memory[address + 1];
  75 }
  76
  77 unsigned int m68k_read_memory_32(unsigned int address)
  78 {
  79         if (address > memory_size - 4) {
  80                 int32_t value;
  81                 value = read_io(address) << 16;
  82                 value |= read_io(address + 2);
  83                 return value;
  84         }
  85         return  (memory[address] << 24)|
  86                 (memory[address + 1] << 16) |
  87                 (memory[address + 2] << 8) |
  88                  memory[address + 3];
  89 }
  90
  91 void m68k_write_memory_8(unsigned int address, unsigned int value)
  92 {
  93         if (address > memory_size - 1) {
  94                 if ((address & 1)) {
  95                         /* write lower (right) byte */
  96                         write_io(address & ~1, 0xff00 | value);
  97                 } else {
  98                         /* write upper (left) byte */
  99                         write_io(address, 0x00ff | (value << 8));
 100                 }
 101                 return;
 102         }
 103         *((uint8_t *)(memory + address)) = value;
 104 }
 105
 106 void m68k_write_memory_16(unsigned int address, unsigned int value)
 107 {
 108         if (address > memory_size - 2) {
 109                 write_io(address, value);
 110                 return;
 111         }
 112         memory[address] = value >> 8;
 113         memory[address + 1] = value;
 114 }
 115
 116 void m68k_write_memory_32(unsigned int address, unsigned int value)
 117 {
 118         if (address > memory_size - 4) {
 119                 write_io(address, value >> 16);
 120                 write_io(address + 2, value);
 121                 return;
 122         }
 123         memory[address] = value >> 24;
 124         memory[address + 1] = value >> 16;
 125         memory[address + 2] = value >> 8;
 126         memory[address + 3] = value;
 127 }
 128
 129 void execute_init(int32_t _memory_size, uint8_t *_memory, uint16_t *_chipreg)
 130 {
 131         memory_size = _memory_size;
 132         memory = _memory;
 133         chipreg = _chipreg;
 134
 135         /* init CPU */
 136         m68k_init();
 137         m68k_set_cpu_type(M68K_CPU_TYPE_68000);
 138 }
 139
 140 void reset_cpu(void)
 141 {
 142         m68k_pulse_reset();
 143 }
 144
 145 int execute_cpu(int irq, const struct cpu_stop stop_at[], int *event)
 146 {
 147         int cycle_count = 0;
 148         int instruction_count = 0;
 149         int i;
 150         uint32_t save_pc;
 151
 152         if (irq) {
 153                 save_pc = REG_PC;
 154                 m68k_set_irq(irq);
 155                 /* loop until we returned from interrupt */
 156                 do {
 157                         /* execute one opcode */
 158                         cycle_count += m68k_execute(0);
 159                         instruction_count++;
 160                 } while (REG_PC != save_pc);
 161 #ifdef DEBUG_CPU
 162                 printf("interrupt %d took %d opcodes\n", irq, instruction_count);
 163 #endif
 164         } else {
 165                 do {
 166                         /* execute one opcode */
 167                         cycle_count += m68k_execute(0);
 168                         instruction_count++;
 169
 170                         /* checking if game does not hit any 'stop_at' break point, give error output */
 171                         if (instruction_count >= 10000000) {
 172                                 if (instruction_count == 10000000)
 173                                         fprintf(stderr, "!!! games seems to got stuck in an endless loop, please fix !!!\n");
 174                                 fprintf(stderr, "program counter at: %06x\n", REG_PC);
 175                                 if (instruction_count == 10000020)
 176                                         break;
 177                         }
 178
 179                         for (i = 0; stop_at[i].event; i++) {
 180                                 if (REG_PC == stop_at[i].pc) {
 181 #ifdef DEBUG_CPU
 182                                         printf("execution to address 0x%06x took %d opcodes\n", REG_PC, instruction_count);
 183 #endif
 184                                         *event = stop_at[i].event;
 185                                         return cycle_count;
 186                                 }
 187                         }
 188                 } while (42);
 189         }
 190
 191         return cycle_count;
 192 }
 193