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mapper1.js
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mapper1.js
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var NES = NES || { };
NES.Mapper1 = function(prgData, chrData) {
var me = this;
var bankData = new Array(3);
var shiftRegister = 0;
var numWrites = 0;
/*
* PRG Mode:
* 0, 1: switch 32 KB at $8000, ignoring low bit of bank number
* 2: fix first bank at $8000 and switch 16 KB bank at $C000
* 3: fix last bank at $C000 and switch 16 KB bank at $8000
*/
var prgMode = 3;
/*
* CHR Mode:
* 0: switch 8 KB at a time
* 1: switch two separate 4 KB banks
*/
var chrMode = 1;
var SRAM = new Uint8Array(0x2000);
this.mirror = 1;
var UTEMP = new Uint8Array(1);
this.readByte = function(address) {
if (address < 0x1000) {
if (chrMode == 0) {
return chrData[((bankData[0] & 0xFE) << 12) + (address % 0x1000)];
}
else {
return chrData[(bankData[0] << 12) + (address % 0x1000)];
}
}
else if (address < 0x2000) {
if (chrMode == 0) {
return chrData[((bankData[0] & 0xFE) << 12) + 0x1000 + (address % 0x1000)];
}
else {
return chrData[(bankData[1] << 12) + (address % 0x1000)];
}
}
else if ((address >= 0x6000) && (address < 0x8000)) {
return SRAM[address - 0x6000];
}
else if ((address >= 0x8000) && (address < 0xC000)) {
if (prgMode == 0 || prgMode == 1) {
return prgData[((bankData[2] & 0xFE) << 14) + (address % 0x4000)];
}
else if (prgMode == 2) {
return prgData[address % 0x4000];
}
else if (prgMode == 3) {
return prgData[(bankData[2] << 14) + (address % 0x4000)];
}
}
else if ((address >= 0xC000) && (address < 0x10000)) {
if (prgMode == 0 || prgMode == 1) {
return prgData[((bankData[2] & 0xFE) << 14) + 0x4000 + (address % 0x4000)];
}
else if (prgMode == 2) {
return prgData[(bankData[2] << 14) + (address % 0x4000)];
}
else if (prgMode == 3) {
return prgData[(((prgData.length >> 14) - 1) << 14) + (address % 0x4000)];
}
}
else {
throw('Invalid read address to mapper1 - ' + address.toString(16));
}
};
this.writeByte = function(address, value) {
UTEMP[0] = value;
if (address < 0x1000) {
if (chrMode == 0) {
chrData[((bankData[0] & 0xFE) << 12) + (address % 0x1000)] = value;
}
else {
chrData[(bankData[0] << 12) + (address % 0x1000)] = value;
}
}
else if (address < 0x2000) {
if (chrMode == 0) {
chrData[((bankData[0] & 0xFE) << 12) + 0x1000 + (address % 0x1000)] = value;
}
else {
chrData[(bankData[1] << 12) + (address % 0x1000)] = value;
}
}
else if (address >= 0x6000 && address < 0x8000) {
SRAM[address - 0x6000] = value;
}
else if (address >= 0x8000 && address < 0x10000) {
if (testBit(UTEMP[0], 7)) {
shiftRegister = 0;
numWrites = 0;
me.mirror = ppu.Mirror.Single0;
prgMode = 3;
chrMode = 0;
}
else {
shiftRegister = shiftRegister >> 1;
shiftRegister = setBit(shiftRegister, 4, testBit(UTEMP[0], 0));
numWrites += 1;
if (numWrites == 5) {
if (address < 0xA000) {
if ((shiftRegister & 0x3) == 0) {
me.mirror = ppu.Mirror.Single0;
}
else if ((shiftRegister & 0x3) == 1) {
me.mirror = ppu.Mirror.Single1;
}
else if ((shiftRegister & 0x3) == 2) {
me.mirror = ppu.Mirror.Vertical;
}
else if ((shiftRegister & 0x3) == 3) {
me.mirror = ppu.Mirror.Horizontal;
}
prgMode = ((shiftRegister >> 2) & 0x3);
chrMode = ((shiftRegister >> 4) & 0x1);
}
else if (address < 0xC000) {
bankData[0] = shiftRegister;
}
else if (address < 0xE000) {
bankData[1] = shiftRegister;
}
else {
bankData[2] = (shiftRegister & 0xF);
}
shiftRegister = 0;
numWrites = 0;
}
}
}
else {
throw('Invalid write address to mapper1 - ' + address.toString(16));
}
};
};