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