nese/src/nes.c

#include <stdio.h>

#include "nes.h"
#include "mapper.h"


uint8_t nes_mem_read(nes* sys, uint16_t addr) {
    uint8_t val = 0;

    if (addr < nes_mem_ppu_start) {
        addr = (addr - nes_mem_ram_start) & (nes_mem_ram_size - 1);
        val = sys->ram[addr];

    } else if (addr < nes_mem_apu_start) {
        addr = (addr - nes_mem_ppu_start) & (nes_ppu_map_size - 1);
        val = nes_ppu_read(&sys->ppu, nes_mem_ppu_start + addr);

    } else if ( nes_input_1_reg == addr ||
                nes_input_2_reg == addr) {
        val = nes_input_read(&sys->input, addr);

    } else if (addr < nes_mem_exp_start) {
        val = nes_apu_read(&sys->apu, addr);

    } else {
        val = nes_map_read(sys->cart.mapper, addr);
    }

    return val;
}

void nes_mem_write(nes* sys, uint16_t addr, uint8_t val) {
    if (addr < nes_mem_ppu_start) {
        addr = (addr - nes_mem_ram_start) & (nes_mem_ram_size - 1);
        sys->ram[addr] = val;

    } else if (addr < nes_mem_apu_start) {
        addr = (addr - nes_mem_ppu_start) & (nes_ppu_map_size - 1);
        nes_ppu_write(&sys->ppu, nes_mem_ppu_start + addr, val);

    } else if (nes_ppu_dma_reg == addr) {
        OAM_LOG("PPU: OAM DMA $%02x00 > $%02x\n", val, sys->ppu.oam_addr);
        uint8_t* buf = (uint8_t*)sys->ppu.oam;
        for (int i = 0; i < nes_ppu_oam_size; ++i) {
            buf[(uint8_t)(i + sys->ppu.oam_addr)] =
                    nes_mem_read(sys, ((uint16_t)val << 8) + i);
        }
        sys->cpu.cycle += 513U;
        // Other subsystem cycles are driven by CPU cycles

    } else if (addr == nes_input_set_reg) {
        nes_input_write(&sys->input, addr, val);

    } else if (addr < nes_mem_exp_start) {
        nes_apu_write(&sys->apu, addr, val);

    } else {
        nes_map_write(sys->cart.mapper, addr, val);
    }
}

static void nes_irq(void* sys, int active) {
    e6502_set_irq(&((nes*)sys)->cpu, active);
}

int nes_init(nes* sys, int audio_freq) {
    e6502_init(&sys->cpu, (e6502_Read*)nes_mem_read,
               (e6502_Write*)nes_mem_write, sys);
    nes_map_set_irq(sys->cart.mapper, nes_irq, sys);
    nes_ppu_init(&sys->ppu, &sys->cart);
    return nes_apu_init(
            &sys->apu,
            nes_clock_master_num / nes_clock_master_den,
            audio_freq,
            (uint8_t(*)(void*, uint16_t))nes_mem_read,
            sys
        );
}

void nes_reset(nes* sys) {
    e6502_reset(&sys->cpu);
    nes_ppu_reset(&sys->ppu);
    nes_apu_reset(&sys->apu);
}

nes_ppu_Result nes_step(nes* sys, int* run) {
    nes_ppu_Result result = ppu_Result_Halt;

    int cpu_run = e6502_step(&sys->cpu);

    if (cpu_run > 0) {
        int master_cycles = cpu_run * nes_clock_cpu_div;

        nes_apu_Result aresult = nes_apu_run(&sys->apu,
                                             master_cycles);

        // TODO: Does this conflict with MMC3?
        e6502_set_irq(&sys->cpu, aresult == apu_Result_IRQ);

        int ppu_cycles = master_cycles / nes_clock_ppu_div;
        result = nes_ppu_run(&sys->ppu, ppu_cycles);

        if (result == ppu_Result_VBlank_On) {
            e6502_set_nmi(&sys->cpu, 1);
        } else if (result == ppu_Result_VBlank_Off) {
            e6502_set_nmi(&sys->cpu, 0);
        }

        if (run) *run = master_cycles;
    }

    return result;
}