nesemu/cpu/cpu.c

176 lines
4.2 KiB
C

//#include "log.h"
#include <assert.h>
#include <string.h>
#include "../include/cpu.h"
#include "cpu.h"
#include "memory.h"
#include "op.h"
#include "decoding.h"
#include "log.h"
/*
* =====================================================================================
*
* Filename: cpu_state.c
*
* Description: 6502 CPU emulator
*
* Version: 1.0
* Created: 2023-09-21 10:10:26 PM
* Revision: none
* Compiler: gcc
*
* Author: William Nolin,
* Organization:
*
* =====================================================================================
*/
CPU cpu_state;
void cpu_init() {
cpu_state.program_counter = 0x8000;
cpu_state.stack_pointer = 0xfd;
cpu_state.accumulator = 0x00;
cpu_state.x = 0x00;
cpu_state.y = 0x00;
cpu_state.status = 0x04;
cpu_state.oam_dma_triggered = false;
cpu_state.nmi_requested = false;
cpu_state.busy_cycle_count = 0;
}
void print_registers(byte op, unsigned long cycle_count) {
log_debug("%#02x %#02x %s \t A:%#02x X:%#02x Y:%#02x F:%#02x SP:%#02x \t [%d]",
cpu_state.program_counter - 1, // The PC as been incremented when printing
op,
get_op_code_name(op),
cpu_state.accumulator,
cpu_state.x,
cpu_state.y,
cpu_state.status,
cpu_state.stack_pointer,
cycle_count);
}
void cpu_process_nmi() {
cpu_stack_push_context();
address handler_addr = mem_get_word(0xfffa);
log_debug("NMI %#04x", handler_addr);
cpu_state.nmi_requested = false;
cpu_state.program_counter = handler_addr;
}
void oam_dma_upload() {
byte page_high_addr = ppu_get_state()->oam_dma_register; // TODO
address page_addr = ((address) page_high_addr) << 8;
byte n = 0xff;
byte *ram_source = mem_get_ptr(page_addr);
byte *oam_destination = ppu_get_state()->oam;
memcpy(oam_destination, ram_source, n);
log_debug("OAM DMA %#04x", page_addr);
cpu_add_cycles(513); // TODO
}
void cpu_cycle() {
if (cpu_state.busy_cycle_count > 0) {
// The last operation is not done yet
cpu_state.busy_cycle_count--;
return;
}
if (cpu_state.nmi_requested) {
cpu_process_nmi();
}
if (cpu_state.oam_dma_triggered) {
oam_dma_upload();
cpu_state.oam_dma_triggered = false;
return;
}
byte op = cpu_get_next_byte();
print_registers(op, system_get_cycles());
process_op_code(op);
}
void cpu_add_cycles(unsigned int cycle_count) {
cpu_state.busy_cycle_count += cycle_count;
}
// === Registers ===
bool cpu_get_flag(byte mask) {
return cpu_state.status & mask;
}
void cpu_set_flag(byte mask, bool set) {
if (set) {
cpu_state.status |= mask;
} else {
cpu_state.status &= ~mask;
}
}
byte cpu_get_next_byte() {
byte next_byte = mem_get_byte(cpu_state.program_counter);
cpu_state.program_counter++;
return next_byte;
}
word cpu_get_next_word() {
word next_word = mem_get_word(cpu_state.program_counter);
cpu_state.program_counter += 2;
return next_word;
}
void cpu_stack_push(byte value) {
assert(cpu_state.stack_pointer > 0);
address mem_addr = CPU_STACK_ADDR | cpu_state.stack_pointer;
mem_set_byte(mem_addr, value);
cpu_state.stack_pointer--;
}
byte cpu_stack_pop() {
assert(cpu_state.stack_pointer < 0xff);
cpu_state.stack_pointer++;
address mem_addr = CPU_STACK_ADDR | cpu_state.stack_pointer;
byte value = mem_get_byte(mem_addr);
return value;
}
void cpu_stack_push_context() {
cpu_stack_push(cpu_state.program_counter >> 8);
cpu_stack_push(cpu_state.program_counter & 0xff);
cpu_stack_push(cpu_state.status);
}
void cpu_stack_pop_context() {
byte value = cpu_stack_pop();
value &= 0xef; // The B mask cannot be set as it is a CPU signal
value |= 0x20; // This value is always set
cpu_state.status = value;
byte lo = cpu_stack_pop();
address pc = cpu_stack_pop() << 8;
pc += lo;
cpu_state.program_counter = pc;
}
void cpu_trigger_oam_dma() {
cpu_state.oam_dma_triggered = true;
}
void cpu_trigger_nmi() {
cpu_state.nmi_requested = true;
}
CPU *cpu_get_state() {
return &cpu_state;
}