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 <string.h>
  24 #include "../libsdl/print.h"
  25 #include "execute.h"
  26 #include "m68k.h"
  27 #include "m68kcpu.h"
  28
  29 //#define DEBUG_CPU
  30
  31 #define IOMASK  0xfffff000
  32 #define IOBASE  0x00dff000
  33
  34 static uint8_t *memory = NULL;
  35 static uint8_t *stop_event = NULL;
  36 static uint32_t memory_size = 0;
  37 static uint16_t *chipreg = NULL;
  38 static uint16_t (*io_read)(uint32_t address) = NULL;
  39 static void (*io_write)(uint32_t address, uint16_t value) = NULL;
  40
  41
  42 static uint16_t read_io_16(unsigned int address)
  43 {
  44 #ifdef DEBUG_CPU
  45         printf("Chip read from 0x%08x\n", address);
  46 #endif
  47         return io_read(address);
  48 }
  49
  50 static void write_io_16(unsigned int address, uint16_t value)
  51 {
  52 #ifdef DEBUG_CPU
  53         printf("Chip write to 0x%08x\n", address);
  54 #endif
  55         if ((address & IOMASK) == IOBASE)
  56                 chipreg[address & ~IOMASK] = value;
  57         io_write(address, value);
  58 }
  59
  60 unsigned int m68k_read_memory_8(unsigned int address)
  61 {
  62         if (address > memory_size - 1) {
  63                 if ((address & 1)) {
  64                         /* read lower (right) byte */
  65                         return read_io_16(address & ~1);
  66                 } else {
  67                         /* read upper (left) byte */
  68                         return read_io_16(address) >> 8;
  69                 }
  70         }
  71         return *((uint8_t *)(memory + address));
  72 }
  73
  74 unsigned int m68k_read_memory_16(unsigned int address)
  75 {
  76         if (address > memory_size - 2) {
  77                 return read_io_16(address);
  78         }
  79         return  (memory[address] << 8) |
  80                  memory[address + 1];
  81 }
  82
  83 unsigned int m68k_read_memory_32(unsigned int address)
  84 {
  85         if (address > memory_size - 4) {
  86                 int32_t value;
  87                 value = read_io_16(address) << 16;
  88                 value |= read_io_16(address + 2);
  89                 return value;
  90         }
  91         return  (memory[address] << 24)|
  92                 (memory[address + 1] << 16) |
  93                 (memory[address + 2] << 8) |
  94                  memory[address + 3];
  95 }
  96
  97 void m68k_write_memory_8(unsigned int address, unsigned int value)
  98 {
  99         if (address > memory_size - 1) {
 100                 if ((address & 1)) {
 101                         /* write lower (right) byte */
 102                         write_io_16(address & ~1, 0xff00 | value);
 103                 } else {
 104                         /* write upper (left) byte */
 105                         write_io_16(address, 0x00ff | (value << 8));
 106                 }
 107                 return;
 108         }
 109         *((uint8_t *)(memory + address)) = value;
 110 }
 111
 112 void m68k_write_memory_16(unsigned int address, unsigned int value)
 113 {
 114         if (address > memory_size - 2) {
 115                 write_io_16(address, value);
 116                 return;
 117         }
 118         memory[address] = value >> 8;
 119         memory[address + 1] = value;
 120 }
 121
 122 void m68k_write_memory_32(unsigned int address, unsigned int value)
 123 {
 124         if (address > memory_size - 4) {
 125                 write_io_16(address, value >> 16);
 126                 write_io_16(address + 2, value);
 127                 return;
 128         }
 129         memory[address] = value >> 24;
 130         memory[address + 1] = value >> 16;
 131         memory[address + 2] = value >> 8;
 132         memory[address + 3] = value;
 133 }
 134
 135 void execute_init(int32_t _memory_size, uint8_t *_memory, uint8_t *_stop_event, uint16_t *_chipreg, uint16_t (*_io_read)(uint32_t address), void (*_io_write)(uint32_t address, uint16_t value), const struct cpu_stop stop_at[])
 136 {
 137         int i;
 138
 139         memory_size = _memory_size;
 140         memory = _memory;
 141         stop_event = _stop_event;
 142         chipreg = _chipreg;
 143         io_read = _io_read;
 144         io_write = _io_write;
 145
 146         /* flag where the cpu shall stop at */
 147         memset(stop_event, 0, _memory_size);
 148         for (i = 0; stop_at[i].event; i++) {
 149                 if (stop_at[i].pc >= memory_size) {
 150                         print_error("stop-event at PC=%x is out of memory=%x\n", stop_at[i].pc, memory_size);
 151                         exit(0);
 152                 }
 153                 stop_event[stop_at[i].pc] = stop_at[i].event;
 154         }
 155
 156         /* init CPU */
 157         m68k_init();
 158         m68k_set_cpu_type(M68K_CPU_TYPE_68000);
 159 }
 160
 161 void reset_cpu(void)
 162 {
 163         m68k_pulse_reset();
 164 }
 165
 166 int execute_cpu(int irq, int *event)
 167 {
 168         int cycle_count = 0;
 169         int instruction_count = 0;
 170         uint32_t save_pc;
 171
 172         if (irq) {
 173                 save_pc = REG_PC;
 174                 m68k_set_irq(irq);
 175                 /* loop until we returned from interrupt */
 176                 do {
 177                         /* execute one opcode */
 178                         cycle_count += m68k_execute(0);
 179                         instruction_count++;
 180                 } while (REG_PC != save_pc);
 181 #ifdef DEBUG_CPU
 182                 printf("interrupt %d took %d opcodes\n", irq, instruction_count);
 183 #endif
 184         } else {
 185                 do {
 186                         /* execute one opcode */
 187                         cycle_count += m68k_execute(0);
 188                         instruction_count++;
 189
 190                         /* checking if game does not hit any 'stop_at' break point, give error output */
 191                         if (instruction_count >= 10000000) {
 192                                 if (instruction_count == 10000000)
 193                                         print_error("!!! games seems to got stuck in an endless loop, please fix !!!\n");
 194                                 fprintf(stderr, "program counter at: %06x\n", REG_PC);
 195                                 if (instruction_count == 10000020)
 196                                         break;
 197                         }
 198
 199                         /* stop execution if there is an event */
 200                         if (REG_PC >= memory_size) {
 201                                 print_error("CPU execution reaches PC=%x that is out of memory=%x\n", REG_PC, memory_size);
 202                                 exit(0);
 203                         }
 204                         if (stop_event[REG_PC]) {
 205                                 *event = stop_event[REG_PC];
 206                                 return cycle_count;
 207                         }
 208                 } while (42);
 209         }
 210
 211         return cycle_count;
 212 }
 213