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 <endian.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
  37 static uint16_t read_io(unsigned int address)
  38 {
  39 #ifdef DEBUG_CPU
  40         printf("Chip read from 0x%08x\n", address);
  41 #endif
  42         return emulate_io_read(address);
  43 }
  44
  45 static void write_io(unsigned int address, uint16_t value)
  46 {
  47 #ifdef DEBUG_CPU
  48         printf("Chip write to 0x%08x\n", address);
  49 #endif
  50         if ((address & IOMASK) == IOBASE)
  51                 chipreg[address & ~IOMASK] = value;
  52         emulate_io_write(address, value);
  53 }
  54
  55 unsigned int m68k_read_memory_8(unsigned int address)
  56 {
  57         if (address > memory_size - 1) {
  58                 if ((address & 1)) {
  59                         /* read lower (right) byte */
  60                         return read_io(address & ~1);
  61                 } else {
  62                         /* read upper (left) byte */
  63                         return read_io(address) >> 8;
  64                 }
  65         }
  66         return *((uint8_t *)(memory + address));
  67 }
  68
  69 unsigned int m68k_read_memory_16(unsigned int address)
  70 {
  71         if (address > memory_size - 2) {
  72                 return read_io(address);
  73         }
  74         return be16toh(*((uint16_t *)(memory + address)));
  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 be32toh(*((uint32_t *)(memory + address)));
  86 }
  87
  88 void m68k_write_memory_8(unsigned int address, unsigned int value)
  89 {
  90         if (address > memory_size - 1) {
  91                 if ((address & 1)) {
  92                         /* write lower (right) byte */
  93                         write_io(address & ~1, 0xff00 | value);
  94                 } else {
  95                         /* write upper (left) byte */
  96                         write_io(address, 0x00ff | (value << 8));
  97                 }
  98                 return;
  99         }
 100         *((uint8_t *)(memory + address)) = value;
 101 }
 102
 103 void m68k_write_memory_16(unsigned int address, unsigned int value)
 104 {
 105         if (address > memory_size - 2) {
 106                 write_io(address, value);
 107                 return;
 108         }
 109         *((uint16_t *)(memory + address)) = htobe16(value);
 110 }
 111
 112 void m68k_write_memory_32(unsigned int address, unsigned int value)
 113 {
 114         if (address > memory_size - 4) {
 115                 write_io(address, value >> 16);
 116                 write_io(address + 2, value);
 117                 return;
 118         }
 119         *((uint32_t *)(memory + address)) = htobe32(value);
 120 }
 121
 122 void execute_init(int32_t _memory_size, uint8_t *_memory, uint16_t *_chipreg)
 123 {
 124         memory_size = _memory_size;
 125         memory = _memory;
 126         chipreg = _chipreg;
 127
 128         /* init CPU */
 129         m68k_init();
 130         m68k_set_cpu_type(M68K_CPU_TYPE_68000);
 131 }
 132
 133 void reset_cpu(void)
 134 {
 135         m68k_pulse_reset();
 136 }
 137
 138 int execute_cpu(int irq, const struct cpu_stop stop_at[], int *event)
 139 {
 140         int cycle_count = 0;
 141         int instruction_count = 0;
 142         int i;
 143         uint32_t save_pc;
 144
 145         if (irq) {
 146                 save_pc = REG_PC;
 147                 m68k_set_irq(irq);
 148                 /* loop until we returned from interrupt */
 149                 do {
 150                         /* execute one opcode */
 151                         cycle_count += m68k_execute(0);
 152                         instruction_count++;
 153                 } while (REG_PC != save_pc);
 154 #ifdef DEBUG_CPU
 155                 printf("interrupt %d took %d opcodes\n", irq, instruction_count);
 156 #endif
 157         } else {
 158                 do {
 159                         /* execute one opcode */
 160                         cycle_count += m68k_execute(0);
 161                         instruction_count++;
 162
 163                         /* checking if game does not hit any 'stop_at' break point, give error output */
 164                         if (instruction_count >= 10000000) {
 165                                 if (instruction_count == 10000000)
 166                                         fprintf(stderr, "!!! games seems to got stuck in an endless loop, please fix !!!\n");
 167                                 fprintf(stderr, "program counter at: %06x\n", REG_PC);
 168                                 if (instruction_count == 10000020)
 169                                         break;
 170                         }
 171
 172                         for (i = 0; stop_at[i].event; i++) {
 173                                 if (REG_PC == stop_at[i].pc) {
 174 #ifdef DEBUG_CPU
 175                                         printf("execution to address 0x%06x took %d opcodes\n", REG_PC, instruction_count);
 176 #endif
 177                                         *event = stop_at[i].event;
 178                                         return cycle_count;
 179                                 }
 180                         }
 181                 } while (42);
 182         }
 183
 184         return cycle_count;
 185 }
 186