6502 CPU emulation. Used in my NES emulator DNES.
Regular instructions are implemented cycle exact. Some illegal instructions are implemented.
The core has been verified with the nestest rom from the NesDev WIKI. It matches up to line 5851 of the nestest log (test of illegal instruction DCP).
See comments in the code below.
#include "d6502.h"
uint8_t memory[0x10000]; // 64kB RAM
static uint8_t cpu_read(uint16_t addr) {
return memory[addr];
}
static void cpu_write(uint16_t addr, uint8_t data) {
memory[addr] = data;
}
int main(int argc, char *argv[]) {
// create struct holding the cpu state
d6502_t cpu;
// initialize cpu state
d6502_init( &cpu );
// set read/write callbacks
cpu.read = cpu_read;
cpu.write = cpu_write;
// trigger reset
d6502_reset(&cpu);
while (1) {
// Every call to d6502_tick() performs a cpu clock cycle.
// d6502_tick() returns the number of clock cycles left for
// the current instruction.
if (d6502_tick(&cpu) == 0) {
// instruction complete.
// print next instruction to stdout
char disassembled_instruction[32];
d6502_disassemble(&cpu, cpu->pc, disassembled_instruction);
printf("%s\n", disassembled_instruction);
}
}
return 0;
}