pkg/chip8/chip8.go

@@ -1,14 +1,17 @@
 package chip8
 
-import "fmt"
+import (
+	"fmt"
+	"math/rand"
+)
 
 const graphicsBufferSize = 64 * 32
 
 type Chip8 struct {
 	addressRegister uint16
-	beepTimer       uint16
+	beepTimer       byte
 	drawRequired    bool
-	delayTimer      uint16
+	delayTimer      byte
 	graphics        [graphicsBufferSize]byte
 	keys            [16]byte
 	memory          [4096]byte
@@ -106,9 +109,9 @@ func (cpu *Chip8) setRegisterTo() {
 	cpu.registers[r] = byte(cpu.opcode & 0xFF)
 }
 
-func (cpu *Chip8) RegisterPlusEqualsNN() {} // QUESTION HERE - WHAT DO IF IT WOULD WRAP ROUND?
+func (cpu *Chip8) registerPlusEqualsNN() {} // QUESTION HERE - WHAT DO IF IT WOULD WRAP ROUND?
 
-func (cpu *Chip8) BitOpsAndMath() {
+func (cpu *Chip8) bitOpsAndMath() {
 	instruction := cpu.opcode & 0x0F
 	regX, regY := cpu.opcode>>8&0x0F, cpu.opcode>>4&0x0F
 	switch instruction {
@@ -166,19 +169,134 @@ func (cpu *Chip8) BitOpsAndMath() {
 	}
 }
 
-func (cpu *Chip8) SkipIfRegistersNotEqual() {
+func (cpu *Chip8) skipIfRegistersNotEqual() {
 	x, y := (cpu.opcode>>8)&0x0F, (cpu.opcode>>4)&0x0F
 	if cpu.registers[x] != cpu.registers[y] {
 		cpu.pc += 2
 	}
 }
 
-func (cpu *Chip8) SetAddressRegister() {
+func (cpu *Chip8) setAddressRegister() {
 	// ANNN
 	// Sets the address register to NNN
 	cpu.addressRegister = cpu.opcode & 0x0FFF
 }
 
+func (cpu *Chip8) jumpToV0PlusAddress() {
+	// BNNN
+	// PC=V0+NNN
+	cpu.pc = uint16(cpu.registers[0]) + (cpu.opcode & 0x0FFF)
+}
+
+func (cpu *Chip8) setRegisterToRand() {
+	// CXNN
+	// Vx = rand() & NN
+	cpu.registers[(cpu.opcode>>8)&0x0F] = byte(cpu.opcode&0xFF) & byte(rand.Intn(256))
+}
+
+func (cpu *Chip8) displaySprite() {
+	// DXYN
+	// Draws a sprite in the graphics buffer
+	// VF is set to 1 if any pixels are flipped and zero otherwise
+	cpu.registers[0x0F] = 0
+	x := int(cpu.registers[(cpu.opcode>>8)&0x0F])
+	y := int(cpu.registers[(cpu.opcode>>4)&0x0F])
+
+	for row := 0; row < int(cpu.opcode&0xF); row++ {
+		pixel := cpu.memory[int(cpu.addressRegister)+row]
+		for column := 0; column < 8; column++ {
+			if pixel&(0x80>>column) != 0 {
+				graphicsPosition := x + column + ((y + row) * 60)
+				if cpu.graphics[graphicsPosition] == 1 {
+					cpu.registers[0xF] = 1
+				}
+				cpu.graphics[graphicsPosition] ^= 1
+			}
+		}
+	}
+	cpu.drawRequired = true
+}
+
+func (cpu *Chip8) SkipOnKeyOpcodes() {
+	opcode := cpu.opcode & 0xFF
+	key := cpu.registers[(cpu.opcode>>8)&0x0F]
+	switch opcode {
+	case 0x9E:
+		// EX9E
+		// skip if key X is pressed
+		if cpu.keys[key] != 0 {
+			cpu.pc += 2
+		}
+	case 0xA1:
+		// EXA1
+		// skip if kkey X is not pressed
+		if cpu.keys[key] == 0 {
+			cpu.pc += 2
+		}
+	}
+}
+
+func (cpu *Chip8) FifteenIndexOpcodes() {
+	instruction := cpu.opcode & 0xFF
+	reg := int(cpu.opcode>>8) & 0xF
+	switch instruction {
+	// FX07
+	// Set VX to the value of the delay timer
+	case 0x07:
+		cpu.registers[reg] = cpu.delayTimer
+	case 0x0A:
+		// FX0A
+		// block + wait for key press
+		for i, val := range cpu.keys {
+			if val != 0 {
+				cpu.registers[reg] = byte(i)
+			}
+		}
+	case 0x15:
+		// FX15
+		// Set delay timer to VX
+		cpu.delayTimer = cpu.registers[reg]
+	case 0x18:
+		// FX18
+		// SET THE BEEP TIMER TO VX
+		// BEEP
+		cpu.beepTimer = cpu.registers[reg]
+	case 0x1E:
+		// FX1E
+		// Add VX to the address register
+		// Set VF to 1 when range overflow
+		if int(cpu.registers[reg])+int(cpu.addressRegister) > 0xFFF {
+			cpu.registers[0x0F] = 1
+		} else {
+			cpu.registers[0x0F] = 0
+		}
+		cpu.addressRegister = uint16((int(cpu.addressRegister) + int(cpu.registers[reg])) & 0xFFF)
+	case 0x29:
+		// FX29
+		// Sets address register to location of char stored in VX
+		cpu.addressRegister = uint16(cpu.registers[reg]) * 5
+	case 0x33:
+		// FX33
+		// Stores BCD representation of VX
+		cpu.memory[cpu.addressRegister] = cpu.registers[reg] / 100
+		cpu.memory[cpu.addressRegister+1] = (cpu.registers[reg] / 10) % 10
+		cpu.memory[cpu.addressRegister+2] = cpu.registers[reg] % 10
+	case 0x55:
+		// FX55
+		// takes values from and including reg X and stores then in memory
+		for i := 0; i <= reg; i++ {
+			cpu.memory[int(cpu.addressRegister)+i] = cpu.registers[i]
+		}
+	case 0x65:
+		// FX65
+		// takes values from memory and stores them in registers
+		for i := 0; i <= reg; i++ {
+			cpu.registers[i] = cpu.memory[int(cpu.addressRegister)+i]
+		}
+	}
+
+}
+
 func main() {
 	fmt.Printf("Hello world!\n")
 	prog := []byte{1, 2, 3, 4}