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 "../libsdl/print.h"
  24 #include "execute.h"
  25 #include "m68k.h"
  26 #include "m68kcpu.h"
  27
  28 //#define DEBUG_CPU
  29
  30 #define IOMASK  0xfffff000
  31 #define IOBASE  0x00dff000
  32
  33 static uint8_t *memory = NULL;
  34 static uint32_t memory_size = 0;
  35 static uint16_t *chipreg = NULL;
  36 static uint16_t (*io_read)(uint32_t address) = NULL;
  37 static void (*io_write)(uint32_t address, uint16_t value) = NULL;
  38
  39
  40 static uint16_t read_io_16(unsigned int address)
  41 {
  42 #ifdef DEBUG_CPU
  43         printf("Chip read from 0x%08x\n", address);
  44 #endif
  45         return io_read(address);
  46 }
  47
  48 static void write_io_16(unsigned int address, uint16_t value)
  49 {
  50 #ifdef DEBUG_CPU
  51         printf("Chip write to 0x%08x\n", address);
  52 #endif
  53         if ((address & IOMASK) == IOBASE)
  54                 chipreg[address & ~IOMASK] = value;
  55         io_write(address, value);
  56 }
  57
  58 unsigned int m68k_read_memory_8(unsigned int address)
  59 {
  60         if (address > memory_size - 1) {
  61                 if ((address & 1)) {
  62                         /* read lower (right) byte */
  63                         return read_io_16(address & ~1);
  64                 } else {
  65                         /* read upper (left) byte */
  66                         return read_io_16(address) >> 8;
  67                 }
  68         }
  69         return *((uint8_t *)(memory + address));
  70 }
  71
  72 unsigned int m68k_read_memory_16(unsigned int address)
  73 {
  74         if (address > memory_size - 2) {
  75                 return read_io_16(address);
  76         }
  77         return  (memory[address] << 8) |
  78                  memory[address + 1];
  79 }
  80
  81 unsigned int m68k_read_memory_32(unsigned int address)
  82 {
  83         if (address > memory_size - 4) {
  84                 int32_t value;
  85                 value = read_io_16(address) << 16;
  86                 value |= read_io_16(address + 2);
  87                 return value;
  88         }
  89         return  (memory[address] << 24)|
  90                 (memory[address + 1] << 16) |
  91                 (memory[address + 2] << 8) |
  92                  memory[address + 3];
  93 }
  94
  95 void m68k_write_memory_8(unsigned int address, unsigned int value)
  96 {
  97         if (address > memory_size - 1) {
  98                 if ((address & 1)) {
  99                         /* write lower (right) byte */
 100                         write_io_16(address & ~1, 0xff00 | value);
 101                 } else {
 102                         /* write upper (left) byte */
 103                         write_io_16(address, 0x00ff | (value << 8));
 104                 }
 105                 return;
 106         }
 107         *((uint8_t *)(memory + address)) = value;
 108 }
 109
 110 void m68k_write_memory_16(unsigned int address, unsigned int value)
 111 {
 112         if (address > memory_size - 2) {
 113                 write_io_16(address, value);
 114                 return;
 115         }
 116         memory[address] = value >> 8;
 117         memory[address + 1] = value;
 118 }
 119
 120 void m68k_write_memory_32(unsigned int address, unsigned int value)
 121 {
 122         if (address > memory_size - 4) {
 123                 write_io_16(address, value >> 16);
 124                 write_io_16(address + 2, value);
 125                 return;
 126         }
 127         memory[address] = value >> 24;
 128         memory[address + 1] = value >> 16;
 129         memory[address + 2] = value >> 8;
 130         memory[address + 3] = value;
 131 }
 132
 133 void execute_init(int32_t _memory_size, uint8_t *_memory, uint16_t *_chipreg, uint16_t (*_io_read)(uint32_t address), void (*_io_write)(uint32_t address, uint16_t value))
 134 {
 135         memory_size = _memory_size;
 136         memory = _memory;
 137         chipreg = _chipreg;
 138         io_read = _io_read;
 139         io_write = _io_write;
 140
 141         /* init CPU */
 142         m68k_init();
 143         m68k_set_cpu_type(M68K_CPU_TYPE_68000);
 144 }
 145
 146 void reset_cpu(void)
 147 {
 148         m68k_pulse_reset();
 149 }
 150
 151 int execute_cpu(int irq, const struct cpu_stop stop_at[], int *event)
 152 {
 153         int cycle_count = 0;
 154         int instruction_count = 0;
 155         int i;
 156         uint32_t save_pc;
 157
 158         if (irq) {
 159                 save_pc = REG_PC;
 160                 m68k_set_irq(irq);
 161                 /* loop until we returned from interrupt */
 162                 do {
 163                         /* execute one opcode */
 164                         cycle_count += m68k_execute(0);
 165                         instruction_count++;
 166                 } while (REG_PC != save_pc);
 167 #ifdef DEBUG_CPU
 168                 printf("interrupt %d took %d opcodes\n", irq, instruction_count);
 169 #endif
 170         } else {
 171                 do {
 172                         /* execute one opcode */
 173                         cycle_count += m68k_execute(0);
 174                         instruction_count++;
 175
 176                         /* checking if game does not hit any 'stop_at' break point, give error output */
 177                         if (instruction_count >= 10000000) {
 178                                 if (instruction_count == 10000000)
 179                                         print_error("!!! games seems to got stuck in an endless loop, please fix !!!\n");
 180                                 fprintf(stderr, "program counter at: %06x\n", REG_PC);
 181                                 if (instruction_count == 10000020)
 182                                         break;
 183                         }
 184
 185                         for (i = 0; stop_at[i].event; i++) {
 186                                 if (REG_PC == stop_at[i].pc) {
 187 #ifdef DEBUG_CPU
 188                                         print_error("execution to address 0x%06x took %d opcodes\n", REG_PC, instruction_count);
 189 #endif
 190                                         *event = stop_at[i].event;
 191                                         return cycle_count;
 192                                 }
 193                         }
 194                 } while (42);
 195         }
 196
 197         return cycle_count;
 198 }
 199