Mapper_24.c

#include "Mapper_24.h"

#include "nes_apu.h"

unsigned char Mapper_24_irq_enabled_l;
unsigned char Mapper_24_irq_enabled_h;
unsigned char Mapper_24_irq_counter;
unsigned char Mapper_24_irq_latch;

void Mapper_24_Init() {
    apu_set_exsound(NES_APU_EXSOUND_VRC6);

    // set CPU bank pointers
    ROMBANK0 = ROMPAGE(0);
    ROMBANK1 = ROMPAGE(1);
    ROMBANK2 = ROMLASTPAGE(1);
    ROMBANK3 = ROMLASTPAGE(0);

    if ( NesHeader.byVRomSize > 0 ) {
        for ( int nPage = 0; nPage < 8; ++nPage )
            PPUBANK[ nPage ] = &VROM[ nPage * 0x400 ];
    }

    Mapper_24_irq_enabled_l = 0;
    Mapper_24_irq_enabled_h = 0;    
    Mapper_24_irq_counter = 0;
    Mapper_24_irq_latch = 0;
}

void Mapper_24_Write(uint16 addr, unsigned char data) {
    switch(addr) {
        case 0x8000: {
            ROMBANK0 = ROMPAGE(data << 1);
            ROMBANK1 = ROMPAGE((data << 1) + 1);
        } break;

        case 0xB003: {
            data &= 0x0C;
            if(data == 0x00) {
                pNesX_Mirroring(MIRRORING_VERTICAL);
            } else if(data == 0x04) {
                pNesX_Mirroring(MIRRORING_HORIZONTAL);
            } else if(data == 0x08) {
                pNesX_Mirroring(MIRRORING_SINGLE_SCREEN_LOW);
            } else if(data == 0x0C) {
                pNesX_Mirroring(MIRRORING_SINGLE_SCREEN_HIGH);                
            }
        } break;

        case 0xC000: {
            ROMBANK2 = ROMPAGE(data);
        } break;

        case 0xD000 ... 0xD003: {
            PPUBANK[(addr & 0xf003) - 0xd000] = VROMPAGE(data);
        } break;

        case 0xE000 ... 0xE003: {
            PPUBANK[(addr & 0xf003) - 0xe000 + 4] = VROMPAGE(data);
        } break;

        case 0xF000: {
            Mapper_24_irq_latch = data;
        } break;

        case 0xF001: {
            Mapper_24_irq_enabled_l = data & 0x1;
            Mapper_24_irq_enabled_h = data & 0x2;
            if (Mapper_24_irq_enabled_h) {
                Mapper_24_irq_counter = Mapper_24_irq_latch;
            }
        } break;

        case 0xF002: {
            Mapper_24_irq_enabled_h = Mapper_24_irq_enabled_l;
        } break;
    }

    ex_write(addr, data);
}

void Mapper_24_HSync() {
    if (Mapper_24_irq_enabled_h) {
        if (Mapper_24_irq_counter == 0xff) {
            IRQ_REQ;
            Mapper_24_irq_counter = Mapper_24_irq_latch;
        } else {
            Mapper_24_irq_counter++;
        }
    }
}