Lesson 01 · The 4KB memory - Build a CHIP-8 Emulator

The 4KB memory

A CHIP-8 machine is mostly one thing - a small block of memory that holds both the program and its data. Today you build that memory and give it a way to read and write a single byte, the foundation every later lesson carves into.

The goal

Create a virtual machine with 4096 bytes of memory and read and write one byte of it.

Start here - the target

TO DO

Scenario: Memory stores and returns a byte

Givena new VM created with NewVM()

Whenthe byte 0xAB is written to address 0x300 with SetByte and then read back with GetByte

Thenthe read returns 0xAB

Andan untouched address such as 0x301 still reads 0x00, and the total memory size is 4096 bytes

Background

Every CHIP-8 program, and everything it works on, lives inside a single 4096-byte memory (0x000 to 0xFFF). There is no separate disk, no heap, no registers-versus-RAM distinction to worry about yet: just one flat array of bytes that the machine reads instructions from and scribbles data into. Building it first means every later piece - the program counter, sprites, the stack - has somewhere to live.

Keep the interface tiny: write a byte at an address, read a byte back. Addresses are 12-bit values (0 through 4095), so a 16-bit unsigned integer holds one comfortably. Starting fully zeroed matters - a fresh machine is blank, and later lessons will rely on unwritten memory reading as 0x00.

Make it work

type VM struct {
  mem [4096]byte // all of CHIP-8's memory, addresses 0x000..0xFFF
}
func NewVM() *VM { return &VM{} }
// named SetByte/GetByte (not Write/ReadByte) to avoid clashing with
// the io.ByteWriter/io.ByteReader signatures go vet checks for
func (v *VM) SetByte(addr uint16, b byte) { v.mem[addr] = b }
func (v *VM) GetByte(addr uint16) byte { return v.mem[addr] }

CheckpointDONE

You have a VM with 4KB of zeroed memory that stores and returns bytes. Commit and stop here.