#ifndef _CRT_SECURE_NO_WARNINGS
	#define _CRT_SECURE_NO_WARNINGS
#endif

#include "dchip8_platform.h"
#include "dqnt.h"
#include "stdio.h"

enum Chip8State
{
	chip8state_init,
	chip8state_load_file,
	chip8state_await_input,
	chip8state_running,
	chip8state_off,
};

typedef struct Chip8CPU
{
	const u16 INIT_ADDRESS = 0x200;

	union {
		u8 registerArray[16];
		struct
		{
			u8 V0;
			u8 V1;
			u8 V2;
			u8 V3;
			u8 V4;
			u8 V5;
			u8 V6;
			u8 V7;
			u8 V8;
			u8 V9;
			u8 VA;
			u8 VB;
			u8 VC;
			u8 VD;
			u8 VE;
			u8 VF;
		};
	};


	// NOTE: Timer that count at 60hz and when set above 0 will count down to 0.
	union {
		u8 dt;
		u8 delayTimer;
	};

	union {
		u8 st;
		u8 soundTimer;
	};

	// NOTE: Maximum value is 0xFFF, or 4095 or 12 bits
	union {
		u16 I;
		u16 indexRegister;
	};

	// NOTE: Maximum value is 0xFFF, or 4095 or 12 bits
	u16 programCounter;

	u8 stackPointer;
	u16 stack[16];

	u8 keyToStoreToRegisterIndex;
	enum Chip8State state;
} Chip8CPU;

FILE_SCOPE Chip8CPU     cpu;
FILE_SCOPE RandPCGState pcgState;

FILE_SCOPE void dchip8_init_memory(u8 *memory)
{
	const u8 PRESET_FONTS[] =
	{
		// "0"
		0xF0, // @@@@ ----
		0x90, // @--@ ----
		0x90, // @--@ ----
		0x90, // @--@ ----
		0xF0, // @@@@----

		// "1"
		0x20, // --@- ----
		0x60, // -@@- ----
		0x20, // --@- ----
		0x20, // --@- ----
		0x70, // -@@@ ----

		// "2"
		0xF0, // @@@@ ----
		0x10, // ---@ ----
		0xF0, // @@@@ ----
		0x80, // @--- ----
		0xF0, // @@@@ ----

		// "3"
		0xF0, // @@@@ ----
		0x10, // ---@ ----
		0xF0, // @@@@ ----
		0x10, // ---@ ----
		0xF0, // @@@@ ----

		// "4"
		0x90, // @--@ ----
		0x90, // @--@ ----
		0xF0, // @@@@ ----
		0x10, // ---@ ----
		0x10, // ---@ ----

		// "5"
		0xF0, // @@@@ ----
		0x80, // @--- ----
		0xF0, // @@@@ ----
		0x10, // ---@ ----
		0xF0, // @@@@ ----

		// "6"
		0xF0, // @@@@ ----
		0x80, // @--- ----
		0xF0, // @@@@ ----
		0x90, // @--@ ----
		0xF0, // @@@@ ----

		// "7"
		0xF0, // @@@@ ----
		0x10, // ---@ ----
		0x20, // --@- ----
		0x40, // -@-- ----
		0x40, // -@-- ----

		// "8"
		0xF0, // @@@@ ----
		0x90, // @--@ ----
		0xF0, // @@@@ ----
		0x90, // @--@ ----
		0xF0, // @@@@ ----

		// "9"
		0xF0, // @@@@ ----
		0x90, // @--@ ----
		0xF0, // @@@@ ----
		0x10, // ---@ ----
		0xF0, // @@@@ ----

		// "A"
		0xF0, // @@@@ ----
		0x90, // @--@ ----
		0xF0, // @@@@ ----
		0x90, // @--@ ----
		0x90, // @--@ ----

		// "B"
		0xE0, // @@@- ----
		0x90, // @--@ ----
		0xE0, // @@@- ----
		0x90, // @--@ ----
		0xE0, // @@@- ----

		// "C"
		0xF0, // @@@@ ----
		0x80, // @--- ----
		0x80, // @--- ----
		0x80, // @--- ----
		0xF0, // @@@@ ----

		// "D"
		0xE0, // @@@- ----
		0x90, // @--@ ----
		0x90, // @--@ ----
		0x90, // @--@ ----
		0xE0, // @@@- ----

		// "E"
		0xF0, // @@@@ ----
		0x80, // @--- ----
		0xF0, // @@@@ ----
		0x80, // @--- ----
		0xF0, // @@@@ ----

		// "F"
		0xF0, // @@@@ ----
		0x80, // @--- ----
		0xF0, // @@@@ ----
		0x80, // @--- ----
		0x80  // @--- ----
	};

	for (i32 i = 0; i < DQNT_ARRAY_COUNT(PRESET_FONTS); i++)
		memory[i] = PRESET_FONTS[i];
}

FILE_SCOPE void dchip8_init_cpu(Chip8CPU *chip8CPU)
{
	// NOTE: Everything before 0x200 is reserved for the actual emulator
	chip8CPU->programCounter = chip8CPU->INIT_ADDRESS;
	chip8CPU->I              = 0;
	chip8CPU->stackPointer   = 0;

	const u32 SEED = 0x8293A8DE;
	dqnt_rnd_pcg_seed(&pcgState, SEED);

	chip8CPU->state = chip8state_load_file;
}

FILE_SCOPE
void dchip8_debug_draw_half_colored_screen_internal(
    PlatformRenderBuffer renderBuffer)
{
	const i32 numPixels = renderBuffer.width * renderBuffer.height;
	u32 *bitmapBuffer   = (u32 *)renderBuffer.memory;
	for (i32 i = 0; i < numPixels; i++)
	{
		// NOTE: Win32 AlphaBlend requires the RGB components to be
		// premultiplied with alpha.
		if (i < numPixels * 0.5f)
		{
			f32 normA = 1.0f;
			f32 normR = (normA * 0.0f);
			f32 normG = (normA * 0.0f);
			f32 normB = (normA * 1.0f);

			u8 r = (u8)(normR * 255.0f);
			u8 g = (u8)(normG * 255.0f);
			u8 b = (u8)(normB * 255.0f);
			u8 a = (u8)(normA * 255.0f);

			u32 color       = (a << 24) | (r << 16) | (g << 8) | (b << 0);
			bitmapBuffer[i] = color;
		}
		else
		{
			f32 normA = 1.0f;
			f32 normR = (normA * 1.0f);
			f32 normG = (normA * 1.0f);
			f32 normB = (normA * 1.0f);

			u8 r = (u8)(normR * 255.0f);
			u8 g = (u8)(normG * 255.0f);
			u8 b = (u8)(normB * 255.0f);
			u8 a = (u8)(normA * 255.0f);

			u32 color       = (a << 24) | (r << 16) | (g << 8) | (b << 0);
			bitmapBuffer[i] = color;
		}
	}
}

FILE_SCOPE void dchip8_init_display(PlatformRenderBuffer renderBuffer)
{
	// Init screen to 0 alpha, and let alpha simulate "turning on a pixel"
	i32 numPixels     = renderBuffer.width * renderBuffer.height;
	u32 *bitmapBuffer = (u32 *)renderBuffer.memory;
	for (i32 i = 0; i < numPixels; i++)
	{
		u8 r = (u8)(0.0f);
		u8 g = (u8)(0.0f);
		u8 b = (u8)(0.0f);
		u8 a = (u8)(0.0f);

		u32 color       = (a << 24) | (r << 16) | (g << 8) | (b << 0);
		bitmapBuffer[i] = color;
	}
}

void dchip8_update(PlatformRenderBuffer renderBuffer, PlatformInput input,
                   PlatformMemory memory)
{
	DQNT_ASSERT(cpu.indexRegister >= 0 && cpu.indexRegister <= 0xFFF);
	DQNT_ASSERT(cpu.programCounter >= 0 && cpu.programCounter <= 0xFFF);
	DQNT_ASSERT(renderBuffer.bytesPerPixel == 4);
	DQNT_ASSERT(memory.permanentMemSize == 4096);

	u8 *mainMem = (u8 *)memory.permanentMem;
	if (cpu.state == chip8state_init)
	{
		dchip8_init_cpu(&cpu);
		dchip8_init_memory(mainMem);
		dchip8_init_display(renderBuffer);
	}

#if 1
	if (cpu.state == chip8state_load_file)
	{
		PlatformFile file = {};
		if (platform_open_file(L"roms/PONG", &file))
		{
			DQNT_ASSERT((cpu.INIT_ADDRESS + file.size) <=
			            memory.permanentMemSize);

			void *loadToAddr = (void *)(&mainMem[cpu.INIT_ADDRESS]);
			if (platform_read_file(file, loadToAddr, (u32)file.size))
			{
				cpu.state = chip8state_running;
			}
			else
			{
				cpu.state = chip8state_off;
			}

			platform_close_file(&file);
		}
	}
#endif

	if (cpu.state == chip8state_await_input)
	{
		const u32 OFFSET_TO_CHIP_CONTROLS = key_7;
		for (i32 i = OFFSET_TO_CHIP_CONTROLS; i < DQNT_ARRAY_COUNT(input.key);
		     i++)
		{
			KeyState checkKey = input.key[i];
			if (checkKey.isDown)
			{
				u8 regIndex = cpu.keyToStoreToRegisterIndex;
				u8 keyVal   = (u8)i - OFFSET_TO_CHIP_CONTROLS;
				DQNT_ASSERT(keyVal >= 0 && keyVal <= 0x0F);

				cpu.registerArray[regIndex] = keyVal;
				cpu.state                   = chip8state_running;
			}
		}
	}

	if (cpu.state == chip8state_running)
	{
		u8 opHighByte = mainMem[cpu.programCounter++];
		u8 opLowByte  = mainMem[cpu.programCounter++];

		u8 opFirstNibble = (opHighByte & 0xF0);
		switch (opFirstNibble)
		{
			case 0x00:
			{
				// CLS - 00E0 - Clear the display
				if (opLowByte == 0xE0)
				{
					dchip8_init_display(renderBuffer);
				}
				// RET - 00EE - Return from subroutine
				else if (opLowByte == 0xEE)
				{
					cpu.programCounter = cpu.stack[--cpu.stackPointer];
				}
			}
			break;

			case 0x10:
			case 0x20:
			{
				u16 loc = ((0x0F & opHighByte) << 8) | opLowByte;
				DQNT_ASSERT(loc <= 0x0FFF);

				// JP addr - 1nnn - Jump to location nnn
				if (opFirstNibble == 0x10)
				{
					// NOTE: Jump to loc, as per below
				}
				// Call addr - 2nnn - Call subroutine at nnn
				else
				{
					DQNT_ASSERT(opFirstNibble == 0x20);
					cpu.stack[cpu.stackPointer++] = cpu.programCounter;
					DQNT_ASSERT(cpu.stackPointer < DQNT_ARRAY_COUNT(cpu.stack));
				}

				cpu.programCounter = loc;
			}
			break;

			case 0x30:
			case 0x40:
			{
				u8 regNum = (0x0F & opHighByte);
				DQNT_ASSERT(regNum < DQNT_ARRAY_COUNT(cpu.registerArray));
				u8 *vx = &cpu.registerArray[regNum];

				u8 valToCheck = opLowByte;

				// SE Vx, byte - 3xkk - Skip next instruction if Vx == kk
				if (opFirstNibble == 0x30)
				{
					if (*vx == valToCheck) cpu.programCounter += 2;
				}
				// SNE Vx, byte - 4xkk - Skip next instruction if Vx == kk
				else
				{
					DQNT_ASSERT(opFirstNibble == 0x40);
					if (*vx != valToCheck) cpu.programCounter += 2;
				}
			}
			break;

			// SE Vx, Vy - 5xy0 - Skip next instruction if Vx = Vy
			case 0x50:
			{
				u8 firstRegNum = (0x0F & opHighByte);
				DQNT_ASSERT(firstRegNum < DQNT_ARRAY_COUNT(cpu.registerArray));

				u8 secondRegNum = (0xF0 & opLowByte) >> 4;
				DQNT_ASSERT(secondRegNum < DQNT_ARRAY_COUNT(cpu.registerArray));

				u8 *vx = &cpu.registerArray[firstRegNum];
				u8 *vy = &cpu.registerArray[secondRegNum];

				if (*vx == *vy) cpu.programCounter += 2;
			}
			break;

			case 0x60:
			case 0x70:
			{
				u8 regNum = (0x0F & opHighByte);
				DQNT_ASSERT(regNum < DQNT_ARRAY_COUNT(cpu.registerArray));
				u8 valToOperateOn = opLowByte;

				u8 *vx = &cpu.registerArray[regNum];
				// LD Vx, byte - 6xkk - Set Vx = kk
				if (opFirstNibble == 0x60)
				{
					*vx = valToOperateOn;
				}
				// ADD Vx, byte - 7xkk - Set Vx = Vx + kk
				else
				{
					DQNT_ASSERT(opFirstNibble == 0x70);
					*vx += valToOperateOn;
				}
			}
			break;

			case 0x80:
			{
				u8 firstRegNum = (0x0F & opHighByte);
				DQNT_ASSERT(firstRegNum < DQNT_ARRAY_COUNT(cpu.registerArray));

				u8 secondRegNum = (0xF0 & opLowByte) >> 4;
				DQNT_ASSERT(secondRegNum < DQNT_ARRAY_COUNT(cpu.registerArray));

				u8 *vx = &cpu.registerArray[firstRegNum];
				u8 *vy = &cpu.registerArray[secondRegNum];

				u8 opFourthNibble = (opLowByte & 0x0F);
				// LD Vx, Vy - 8xy0 - Set Vx = Vy
				if (opFourthNibble == 0x00)
				{
					*vx = *vy;
				}
				// OR Vx, Vy - 8xy1 - Set Vx = Vx OR Vy
				else if (opFourthNibble == 0x01)
				{
					u8 result = (*vx | *vy);
					*vx       = result;
				}
				// AND Vx, Vy - 8xy2 - Set Vx = Vx AND Vy
				else if (opFourthNibble == 0x02)
				{
					u8 result = (*vx & *vy);
					*vx       = result;
				}
				// XOR Vx, Vy - 8xy3 - Set Vx = Vx XOR Vy
				else if (opFourthNibble == 0x03)
				{
					u8 result = (*vx ^ *vy);
					*vx       = result;
				}
				// ADD Vx, Vy - 8xy4 - Set Vx = Vx + Vy, set VF = carry
				else if (opFourthNibble == 0x04)
				{
					u16 result = (*vx + *vy);
					*vx = (result > 255) ? (u8)(result - 256) : (u8)result;

					cpu.VF = (result > 255) ? 1 : 0;
				}
				// SUB Vx, Vy - 8xy5 - Set Vx = Vx - Vy, set VF = NOT borrow
				else if (opFourthNibble == 0x05)
				{
					if (*vx > *vy)
					{
						cpu.VF = 1;
						*vx -= *vy;
					}
					else
					{
						cpu.VF = 0;
						*vx = (u8)(256 + *vx - *vy);
					}

				}
				// SHR Vx {, Vy} - 8xy6 - Set Vx = Vx SHR 1
				else if (opFourthNibble == 0x06)
				{
					if (*vx & 1)
						cpu.VF = 1;
					else
						cpu.VF = 0;

					*vx >>= 1;
				}
				// SUBN Vx {, Vy} - 8xy7 - Set Vx = Vy - Vx, set VF = NOT borrow
				else if (opFourthNibble == 0x07)
				{
					if (*vy > *vx)
					{
						cpu.VF = 1;
						*vx    = *vy - *vx;
					}
					else
					{
						cpu.VF = 0;
						*vx    = (u8)(256 + *vy - *vx);
					}

				}
				// SHL Vx {, Vy} - 8xyE - Set Vx = SHL 1
				else
				{
					DQNT_ASSERT(opFourthNibble == 0x0E);
					if ((*vx >> 7) == 1)
						cpu.VF = 1;
					else
						cpu.VF = 0;

					*vx <<= 1;
				}
			}
			break;

			// SNE Vx, Vy - 9xy0 - Skip next instruction if Vx != Vy
			case 0x90:
			{
				u8 firstRegNum = (0x0F & opHighByte);
				DQNT_ASSERT(firstRegNum < DQNT_ARRAY_COUNT(cpu.registerArray));

				u8 secondRegNum = (0xF0 & opLowByte) >> 4;
				DQNT_ASSERT(secondRegNum < DQNT_ARRAY_COUNT(cpu.registerArray));

				u8 *vx = &cpu.registerArray[firstRegNum];
				u8 *vy = &cpu.registerArray[secondRegNum];

				if (*vx != *vy) cpu.programCounter += 2;
			}
			break;

			// LD I, addr - Annn - Set I = nnn
			case 0xA0:
			{
				u16 valToSet       = ((0x0F & opHighByte) << 8) | opLowByte;
				cpu.indexRegister = valToSet;
			}
			break;

			// JP V0, addr - Bnnn - Jump to location (nnn + V0)
			case 0xB0:
			{
				u16 addr = (((0x0F & opHighByte) << 8) | opLowByte) + cpu.V0;
				cpu.programCounter = addr;
			}
			break;

			// RND Vx, byte - Cxkk - Set Vx = random byte AND kk
			case 0xC0:
			{
				u8 regNum = (0x0F & opHighByte);
				DQNT_ASSERT(regNum < DQNT_ARRAY_COUNT(cpu.registerArray));
				u8 *vx = &cpu.registerArray[regNum];

				u8 randNum = (u8)dqnt_rnd_pcg_range(&pcgState, 0, 255);
				u8 andBits = opLowByte;
				DQNT_ASSERT(randNum >= 0 && randNum <= 255);

				*vx = (randNum & andBits);
			}
			break;

			// DRW Vx, Vy, nibble - Dxyn - Display n-byte sprite starting at mem
			// location I at (Vx, Vy), set VF = collision
			case 0xD0:
			{
				u8 xRegister           = (0x0F & opHighByte);
				u8 yRegister           = (0xF0 & opLowByte) >> 4;
				DQNT_ASSERT(xRegister < DQNT_ARRAY_COUNT(cpu.registerArray) &&
				            yRegister < DQNT_ARRAY_COUNT(cpu.registerArray));

				u8 initPosX = cpu.registerArray[xRegister];
				u8 initPosY = cpu.registerArray[yRegister];

				u8 readNumBytesFromMem = (0x0F & opLowByte);
				// NOTE: can't be more than 16 in Y according to specs.
				DQNT_ASSERT(readNumBytesFromMem < 16);

				u8 *renderBitmap          = (u8 *)renderBuffer.memory;
				const i32 BYTES_PER_PIXEL = renderBuffer.bytesPerPixel;
				i32 pitch = renderBuffer.width * BYTES_PER_PIXEL;

				for (i32 i = 0; i < readNumBytesFromMem; i++)
				{
					u8 spriteBytes = mainMem[cpu.indexRegister + i];
					u8 posY        = initPosY + (u8)i;

					if (posY >= renderBuffer.height) posY = 0;

					const i32 ALPHA_BYTE_INTERVAL = renderBuffer.bytesPerPixel;
					const i32 BITS_IN_BYTE        = 8;
					i32 baseBitShift              = BITS_IN_BYTE - 1;
					for (i32 shift = 0; shift < BITS_IN_BYTE; shift++)
					{
						u8 posX = initPosX + (u8)shift;

						if (posX >= renderBuffer.width) posX = 0;
						u32 bitmapOffset =
						    (posX * BYTES_PER_PIXEL) + (posY * pitch);

						// NOTE: Since we are using a 4bpp bitmap, let's use the
						// alpha channel to determine if a pixel is on or not.
						u32 *pixel  = (u32 *)(&renderBitmap[bitmapOffset]);
						u8 alphaBit = (*pixel >> 24);

						DQNT_ASSERT(alphaBit == 0 || alphaBit == 255);
						bool pixelWasOn = (alphaBit == 255) ? true : false;

						i32 bitShift   = baseBitShift - shift;
						bool spriteBit = ((spriteBytes >> bitShift) & 1);
						bool pixelIsOn = (pixelWasOn ^ spriteBit);

						// NOTE: If caused a pixel to XOR into off, then this is
						// known as a "collision" in chip8
						if (pixelWasOn && !pixelIsOn)
						{
							cpu.VF = 1;
						}
						else
						{
							cpu.VF = 0;
						}

						if (pixelIsOn)
						{
							*pixel = 0xFFFFFFFF;
						}
						else
						{
							*pixel = 0;
						}
					}
				}
			}
			break;

			case 0xE0:
			{
				u8 regNum = (0x0F & opHighByte);
				DQNT_ASSERT(regNum < DQNT_ARRAY_COUNT(cpu.registerArray));
				u8 vx = cpu.registerArray[regNum];
				DQNT_ASSERT(vx >= 0 && vx <= 0x0F);

				const u32 KEY_OFFSET_TO_START_CONTROLS = key_7;
				DQNT_ASSERT((KEY_OFFSET_TO_START_CONTROLS + vx) <
				            DQNT_ARRAY_COUNT(input.key));

				KeyState checkKey =
				    input.key[KEY_OFFSET_TO_START_CONTROLS + vx];
				bool skipNextInstruction = false;
				// SKP Vx - Ex9E - Skip next instruction if key with the value
				// of Vx is pressed
				if (opLowByte == 0x9E)
				{
					skipNextInstruction = checkKey.isDown;
				}
				// SKNP Vx - ExA1 - Skip next instruction if key with the value
				// of Vx is not pressed
				else
				{
					DQNT_ASSERT(opLowByte == 0xA1);
					skipNextInstruction = !checkKey.isDown;
				}

				if (skipNextInstruction) cpu.programCounter += 2;
			}
			break;

			case 0xF0:
			{
				u8 regNum = (0x0F & opHighByte);
				DQNT_ASSERT(regNum < DQNT_ARRAY_COUNT(cpu.registerArray));
				u8 *vx = &cpu.registerArray[regNum];

				// LD Vx, DT - Fx07 - Set Vx = delay timer value
				if (opLowByte == 0x07)
				{
					*vx = cpu.delayTimer;
				}
				// LD Vx, K - Fx0A - Wait for a key press, store the value of
				// the key in Vx
				else if (opLowByte == 0x0A)
				{
					cpu.state                     = chip8state_await_input;
					cpu.keyToStoreToRegisterIndex = regNum;
				}
				// LD DT, Vx - Fx15 - Set delay timer = Vx
				else if (opLowByte == 0x15)
				{
					cpu.delayTimer = *vx;
				}
				// LD ST, Vx - Fx18 - Set sound timer = Vx
				else if (opLowByte == 0x18)
				{
					cpu.soundTimer = *vx;
				}
				// ADD I, Vx - Fx1E - Set I = I + Vx
				else if (opLowByte == 0x1E)
				{
					cpu.indexRegister += *vx;
				}
				// LD F, Vx - Fx29 - Set I = location of sprite for digit Vx
				else if (opLowByte == 0x29)
				{
					u8 hexCharFromFontSet = *vx;
					DQNT_ASSERT(hexCharFromFontSet >= 0x00 &&
					            hexCharFromFontSet <= 0x0F);

					const u8 BITS_IN_BYTE     = 8;
					u8 fontSizeInMem          = BITS_IN_BYTE * 5;
					u16 startMemAddrOfFontSet = 0;

					cpu.I = startMemAddrOfFontSet +
					        (hexCharFromFontSet * fontSizeInMem);
				}
				// LD B, Vx - Fx33 - Store BCD representations of Vx in memory
				// locations I, I+1 and I+2
				else if (opLowByte == 0x33)
				{
					DQNT_ASSERT(regNum < DQNT_ARRAY_COUNT(cpu.registerArray));
					u8 vxVal = *vx;

					const i32 NUM_DIGITS_IN_HUNDREDS = 3;
					for (i32 i = 0; i < NUM_DIGITS_IN_HUNDREDS; i++)
					{
						u8 rem = vxVal % 10;
						vxVal /= 10;

						mainMem[cpu.I + ((NUM_DIGITS_IN_HUNDREDS-1) - i)] = rem;
					}
				}
				// LD [I], Vx - Fx55 - Store register V0 through Vx in memory
				// starting at location I.
				else if (opLowByte == 0x55)
				{
					for (u32 regIndex = 0; regIndex <= regNum; regIndex++)
					{
						u32 mem_offset = regIndex;
						mainMem[cpu.indexRegister + mem_offset] =
						    cpu.registerArray[regIndex];
					}
				}
				// LD [I], Vx - Fx65 - Read registers V0 through Vx from memory
				// starting at location I.
				else
				{
					DQNT_ASSERT(opLowByte == 0x65);
					for (u32 regIndex = 0; regIndex <= regNum; regIndex++)
					{
						u32 mem_offset = regIndex;
						cpu.registerArray[regIndex] =
						    mainMem[cpu.indexRegister + mem_offset];
					}
				}
			}
			break;
		};

		if (cpu.delayTimer > 0) cpu.delayTimer--;

		// TODO(doyle): This needs to play a buzzing sound whilst timer > 0
		if (cpu.soundTimer > 0) cpu.soundTimer--;
	}

}