go/chip8-emulator
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emulator step

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This commit is contained in:
Jairinho 2022-02-23 16:45:56 -03:00
parent da804769c6
commit 80ff284c0d
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GPG Key ID: 954589B18A21D5B6
2 changed files with 46 additions and 8 deletions
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19
chip8/chip8.go
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@ -1,5 +1,7 @@
package chip8
import "encoding/binary"
const (
MemorySize = 4096 // 4KB of memory
StackSize = 16
@ -41,3 +43,20 @@ func (emulator *Emulator) Reset() {
emulator.Timer.Sound = 0
copy(emulator.Memory[ProgramAddress:], emulator.ROM)
}
func (emulator *Emulator) Step() {
instruction := binary.BigEndian.Uint16(emulator.Memory[emulator.PC:])
switch instruction & 0xF000 {
case 0x1000: // 1nnn - JP addr
emulator.Jump(instruction & 0x0FFF)
case 0x2000: // 2nnn - CALL addr
emulator.Call(instruction & 0x0FFF)
case 0x3000: // 3xkk - SE Vx, byte
emulator.SkipEqual(uint8(instruction&0x0F00>>8), uint8(instruction&0x00FF))
case 0x4000: // 4xkk - SNE Vx, byte
emulator.SkipNotEqual(uint8(instruction&0x0F00>>8), uint8(instruction&0x00FF))
case 0x5000: // 5xy0 - SE Vx, Vy
emulator.SkipRegistersEqual(uint8(instruction&0x0F00>>8), uint8(instruction&0x00F0>>4))
}
}

35
chip8/instructions.go
View File

@ -9,31 +9,50 @@ func (emulator *Emulator) Return() {
emulator.StackPop()
}
func (emulator *Emulator) Jump(addr uint16) {
emulator.PC = addr
// Jump to location nnn.
//
// The interpreter sets the program counter to nnn.
func (emulator *Emulator) Jump(nnn uint16) {
emulator.PC = nnn
}
func (emulator *Emulator) Call(addr uint16) {
// Call subroutine at nnn.
//
// The interpreter increments the stack pointer, then puts the current PC
// on the top of the stack. The PC is then set to nnn.
func (emulator *Emulator) Call(nnn uint16) {
emulator.StackPush()
emulator.PC = addr
emulator.PC = nnn
}
func (emulator *Emulator) SkipEqual(x uint8, value uint8) {
if emulator.V[x] == value {
// Skip next instruction if Vx = kk.
//
// The interpreter compares register Vx to kk, and if they are equal,
// increments the program counter by 2.
func (emulator *Emulator) SkipEqual(x uint8, kk uint8) {
if emulator.V[x] == kk {
emulator.PC += InstructionSize * 2
} else {
emulator.PC += InstructionSize
}
}
func (emulator *Emulator) SkipNotEqual(x uint8, value uint8) {
if emulator.V[x] != value {
// Skip next instruction if Vx != kk.
//
// The interpreter compares register Vx to kk, and if they are not equal,
// increments the program counter by 2.
func (emulator *Emulator) SkipNotEqual(x uint8, kk uint8) {
if emulator.V[x] != kk {
emulator.PC += InstructionSize * 2
} else {
emulator.PC += InstructionSize
}
}
// Skip next instruction if Vx = Vy.
//
// The interpreter compares register Vx to register Vy, and if they are equal,
// increments the program counter by 2.
func (emulator *Emulator) SkipRegistersEqual(x uint8, y uint8) {
if emulator.V[x] == emulator.V[y] {
emulator.PC += InstructionSize * 2