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standard_memory.go
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standard_memory.go
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package chip8
import (
"fmt"
"io"
)
const memSize = 0xFFF
const romAddressOffset = 0x200
const romSize = memSize - romAddressOffset
const fontAddressOffset = 0x0
// Sprite of fonts
var fonts = []byte{
// 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,
}
// StandardMemory implements interface Memory
type StandardMemory struct {
mem [memSize]byte
log io.Writer
}
type ConfigMemory struct {
Rom io.Reader
Log io.Writer
}
// NewStandardMemory is a function that receive a config as param and return a pointer to StandardMemory
func NewStandardMemory(config *ConfigMemory) *StandardMemory {
sm := &StandardMemory{log: config.Log}
sm.loadFonts()
sm.loadGame(config.Rom)
return sm
}
func (sm *StandardMemory) loadFonts() {
for i := 0; i < len(fonts); i++ {
sm.mem[fontAddressOffset+i] = fonts[i]
}
}
func (sm *StandardMemory) loadGame(rom io.Reader) {
buf := [romSize]byte{}
n, err := rom.Read(buf[:])
if err != nil {
panic(err)
}
if n == 0 {
return
}
for i := 0; i < n; i++ {
sm.mem[romAddressOffset+i] = buf[i]
}
}
// Log writes values of memory to "log" of Memory
func (sm *StandardMemory) Log() {
sm.log.Write([]byte(fmt.Sprintf("memory: %v\n", sm.mem)))
}
// SaveBCD convert vx byte to decimal and save each digit on I, I+1 and I+2
func (sm *StandardMemory) SaveBCD(vx byte, i uint16) {
sm.mem[i] = vx / 100
sm.mem[i+1] = (vx % 100) / 10
sm.mem[i+2] = (vx % 10)
}
// Save saves the registers on memory starting on register I
func (sm *StandardMemory) Save(register []byte, i uint16) {
for idx, reg := range register {
sm.mem[int(i)+idx] = reg
}
}
// Load loads to the register from of memory starting on register I
func (sm *StandardMemory) Load(register []byte, i uint16) {
for idx := 0; idx < len(register); idx++ {
register[idx] = sm.mem[int(i)+idx]
}
}
// LoadInstruction returns the instruction addressed by register PC
func (sm *StandardMemory) LoadInstruction(pc uint16) Instruction {
return Instruction{sm.mem[pc], sm.mem[pc+1]}
}
// LoadChar returns the address to char VX
func (sm *StandardMemory) LoadChar(vx byte) uint16 {
if vx > 0xF {
return 0
}
return uint16(vx * 5)
}
// LoadSprit returns the sprite on position I
func (sm *StandardMemory) LoadSprite(i uint16) byte {
return sm.mem[i]
}