LED flasher from Ben Eater's 6502 part 2 video

rom.sc

//> using scala "3.2.1"
//> using lib "org.scodec::scodec-bits:1.1.34"
//> using lib "co.fs2::fs2-io:3.4.0"

import scodec.bits.*
import cats.effect.IO
import cats.effect.unsafe.implicits.global
import fs2.{Stream, Chunk}
import fs2.io.file.{Files, Path}

def instructions(code: String): ByteVector =
  Stream(code)
    .through(fs2.text.lines)
    .map(_.split("#").head)
    .map(ByteVector.fromHex(_).get)
    .compile.fold(ByteVector.empty)(_ ++ _)

val code = instructions("""
a9 ff     # lda #$ff
8d 02 60  # sta $6002

a9 55     # lda #$55
8d 00 60  # sta $6000

a9 aa     # lda #$aa
8d 00 60  # sta $6000

4c 05 80  # jmp $8005
""")

val rom = code ++ ByteVector.fill(32768 - code.size)(0xea)

val prom = rom.patch(0x7ffc, hex"0080")

Stream.chunk(Chunk.byteVector(prom)).through(Files[IO].writeAll(Path("rom.bin"))).compile.drain.unsafeRunSync()