VRC6Mapper.java

/*
 * HalfNES by Andrew Hoffman
 * Licensed under the GNU GPL Version 3. See LICENSE file
 */
package com.grapeshot.halfnes.mappers;

import com.grapeshot.halfnes.*;
import com.grapeshot.halfnes.audio.*;

public class VRC6Mapper extends Mapper {

    int[][] registerselectbits = {{0, 1}, {1, 0}};
    int[] registers;
    int prgbank0, prgbank1 = 0;
    int[] chrbank = {0, 0, 0, 0, 0, 0, 0, 0};
    boolean irqmode, irqenable, irqack, firedinterrupt = false;
    int irqreload, irqcounter = 22;
    VRC6SoundChip sndchip;
    boolean hasInitSound = false;

    public VRC6Mapper(int mappernum) {
        super();
        sndchip = new VRC6SoundChip();

        switch (mappernum) {
            //vrc6 has 2 different mapper numbers, for 2 different ways to assign the registers
            case 24:
                registers = registerselectbits[0];
                break;
            case 26:
            default:
                registers = registerselectbits[1];
                break;

        }
    }

    @Override
    public void loadrom() throws BadMapperException {
        super.loadrom();
        // needs to be in every mapper. Fill with initial cfg
        for (int i = 1; i <= 32; ++i) {
            //map last banks in to start off
            prg_map[32 - i] = prgsize - (1024 * i);
        }
        for (int i = 0; i < 8; ++i) {
            chr_map[i] = (1024 * i) & (chrsize - 1);
        }
    }

    @Override
    public final void cartWrite(final int addr, final int data) {
        if (addr < 0x8000 || addr > 0xffff) {
            super.cartWrite(addr, data);
            return;
        }

        final boolean bit0 = ((addr & (1 << registers[0])) != 0);
        final boolean bit1 = ((addr & (1 << registers[1])) != 0);
        switch (addr >> 12) {
            case 0x8:
                //8000-8003: prg bank 0 select
                prgbank0 = data;
                setbanks();
                break;
            case 0x9:
            case 0xa:
                //sound registers here
                sndchip.write((addr & 0xf000) + (bit1 ? 2 : 0) + (bit0 ? 1 : 0), data);
                break;
            case 0xc:
                //c000-c003: prg bank 1 select
                prgbank1 = data;
                setbanks();
                break;
            case 0xb:
                if (bit0 && bit1) {
                    //mirroring select
                    switch ((data >> 2) & 3) {
                        case 0:
                            setmirroring(Mapper.MirrorType.V_MIRROR);
                            break;
                        case 1:
                            setmirroring(Mapper.MirrorType.H_MIRROR);
                            break;
                        case 2:
                            setmirroring(Mapper.MirrorType.SS_MIRROR0);
                            break;
                        case 3:
                            setmirroring(Mapper.MirrorType.SS_MIRROR1);
                            break;
                    }
                } else {
                    //expansion sound register here as well
                    sndchip.write((addr & 0xf000) + (bit1 ? 2 : 0) + (bit0 ? 1 : 0), data);
                }
                break;
            case 0xd:
                //character bank selects
                chrbank[(bit1 ? 2 : 0) + (bit0 ? 1 : 0)] = data;
                setbanks();
                break;
            case 0xe:
                chrbank[(bit1 ? 2 : 0) + (bit0 ? 1 : 0) + 4] = data;
                setbanks();
                break;
            case 0xf:
                //irq control
                if (!bit1) {
                    if (!bit0) {
                        irqreload = data;
                    } else {
                        irqack = ((data & (utils.BIT0)) != 0);
                        irqenable = ((data & (utils.BIT1)) != 0);
                        irqmode = ((data & (utils.BIT2)) != 0);
                        if (irqenable) {
                            irqcounter = irqreload;
                            prescaler = 341;
                        }
                        if (firedinterrupt) {
                            --cpu.interrupt;
                        }
                        firedinterrupt = false;
                    }
                } else {
                    if (!bit0) {
                        irqenable = irqack;
                        if (firedinterrupt) {
                            --cpu.interrupt;
                        }
                        firedinterrupt = false;
                    }
                }

        }
    }

    private void setbanks() {
        //map prg banks
        //last 8k fixed to end of rom
        for (int i = 1; i <= 8; ++i) {
            prg_map[32 - i] = prgsize - (1024 * i);
        }
        //first bank set to prg0 register
        for (int i = 0; i < 16; ++i) {
            prg_map[i] = (1024 * (i + 16 * prgbank0)) % prgsize;
        }
        //second bank set to prg1 register
        for (int i = 0; i < 8; ++i) {
            prg_map[i + 16] = (1024 * (i + 8 * prgbank1)) % prgsize;
        }

        //map chr banks
        for (int i = 0; i < 8; ++i) {
            setppubank(1, i, chrbank[i]);
        }
    }

    private void setppubank(final int banksize, final int bankpos, final int banknum) {
//        System.err.println(banksize + ", " + bankpos + ", "+ banknum);
        for (int i = 0; i < banksize; ++i) {
            chr_map[i + bankpos] = (1024 * ((banknum) + i)) % chrsize;
        }
//        utils.printarray(chr_map);
    }

    int prescaler = 341;

    @Override
    public void cpucycle(int cycles) {
        if (irqenable) {
            if (irqmode) {
                scanlinecount();
                //clock regardless of prescaler state
            } else {
                prescaler -= 3;
                if (prescaler <= 0) {
                    prescaler += 341;
                    scanlinecount();
                }
            }
        }
    }

    public void scanlinecount() {
        if (!hasInitSound) {
            //tiny hack, because the APU is not initialized until AFTER this happens
            //TODO: this really should not need to be here.
            cpuram.apu.addExpnSound(sndchip);
            hasInitSound = true;
        }
        if (irqenable) {
            if (irqcounter == 255) {
                irqcounter = irqreload;
                //System.err.println("Interrupt @ Scanline " + scanline + " reload " + irqreload);
                if (!firedinterrupt) {
                    ++cpu.interrupt;
                }
                firedinterrupt = true;
            } else {
                ++irqcounter;
            }
        }
    }
}