153 lines
3.5 KiB
Go
153 lines
3.5 KiB
Go
package chip8
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import (
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"encoding/binary"
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"image"
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"math"
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)
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const (
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MemorySize = 4096 // 4KB of memory
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InstructionSize = 2
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)
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const (
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ProgramAddress = uint16(0x0200)
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)
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const (
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Width = 64
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Height = 32
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FPS = 60
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)
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type Emulator struct {
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V [16]uint8 // general registers
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I uint16 // address register
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PC uint16 // program counter
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DT uint8 // delay timer
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ST uint8 // sound timer
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Stack *Stack // very simple stack
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Memory [MemorySize]uint8 // 4KB of system RAM
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ROM []uint8 // game rom
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Display *image.Gray // display buffer
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}
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func NewEmulator() *Emulator {
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emulator := new(Emulator)
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emulator.Stack = NewStack()
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emulator.Display = image.NewGray(image.Rect(0, 0, Width, Height))
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emulator.Reset()
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return emulator
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}
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func (emulator *Emulator) Reset() {
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emulator.V = [16]uint8{}
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emulator.I = 0
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emulator.PC = ProgramAddress
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emulator.DT = 0
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emulator.ST = 0
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emulator.Memory = [MemorySize]uint8{}
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// clean stack
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emulator.Stack.Clear()
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// clean display
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emulator.ClearScreen()
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// load rom on memory
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copy(emulator.Memory[ProgramAddress:], emulator.ROM)
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}
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func (emulator *Emulator) Cycle() {
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pc := emulator.PC
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emulator.DT = uint8(math.Max(0, float64(emulator.DT)-1))
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emulator.ST = uint8(math.Max(0, float64(emulator.ST)-1))
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instruction := binary.BigEndian.Uint16(emulator.Memory[emulator.PC:])
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nnn := instruction & 0x0FFF
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n := uint8(instruction & 0x000F)
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kk := uint8(instruction & 0x00FF)
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x := uint8(instruction & 0x0F00 >> 8)
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y := uint8(instruction & 0x00F0 >> 4)
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switch instruction & 0xF000 >> 12 {
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case 0x0:
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switch instruction & 0x00FF {
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case 0xE0: // 00E0 - CLS
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emulator.ClearScreen()
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case 0xEE: // 00EE - RET
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emulator.Return()
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}
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case 0x1: // 1nnn - JP addr
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emulator.Jump(nnn)
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case 0x2: // 2nnn - CALL addr
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emulator.Call(nnn)
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case 0x3: // 3xkk - SE Vx, byte
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emulator.SkipEqualByte(x, kk)
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case 0x4: // 4xkk - SNE Vx, byte
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emulator.SkipNotEqualByte(x, kk)
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case 0x5: // 5xy0 - SE Vx, Vy
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emulator.SkipEqual(x, y)
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case 0x6: // 6xkk - LD Vx, byte
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emulator.LoadByte(x, kk)
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case 0x7: // 7xkk - ADD Vx, byte
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emulator.AddByte(x, kk)
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case 0x8:
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switch instruction & 0x000F {
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case 0x0: // 8xy0 - LD Vx, Vy
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emulator.Load(x, y)
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case 0x1: // 8xy1 - OR Vx, Vy
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emulator.Or(x, y)
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case 0x2: // 8xy2 - AND Vx, Vy
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emulator.And(x, y)
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case 0x3: // 8xy3 - XOR Vx, Vy
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emulator.Xor(x, y)
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case 0x4: // 8xy4 - ADD Vx, Vy
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emulator.Add(x, y)
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case 0x5: // 8xy5 - SUB Vx, Vy
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emulator.Sub(x, y)
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case 0x6: // 8xy6 - SHR Vx {, Vy}
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emulator.ShiftRight(x)
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case 0x7: // 8xy7 - SUBN Vx, Vy
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emulator.SubN(x, y)
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case 0xE: // 8xyE - SHL Vx {, Vy}
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emulator.ShiftLeft(x)
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}
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case 0x9: // 9xy0 - SNE Vx, Vy
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emulator.SkipNotEqual(x, y)
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case 0xA: // Annn - LD I, nnn
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emulator.LoadI(nnn)
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case 0xB: // Bnnn - JP V0, nnn
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emulator.JumpV0(nnn)
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case 0xC: // Cxkk - RND Vx, kk
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emulator.Random(x, kk)
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case 0xD: // Dxyn - DRW Vx, Vy, n
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emulator.Draw(x, y, n)
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case 0xE:
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switch instruction & 0x00FF {
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case 0x9E: // SKP Vx
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case 0xA1: // SKNP Vx
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}
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case 0xF:
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switch instruction & 0x00FF {
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case 0x07: // LD Vx, DT
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case 0x0A: // LD Vx, K
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case 0x15: // LD DT, Vx
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case 0x18: // LD ST, Vx
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case 0x1E: // ADD I, Vx
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case 0x29: // LD F, Vx
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case 0x33: // LD B, Vx
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case 0x55: // LD [I], Vx
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case 0x65: // LD Vx, [I]
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}
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}
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// if the program counter is unchanged and isn't a loop, read next instruction
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if emulator.PC == pc && nnn != pc {
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emulator.PC += InstructionSize
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}
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}
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