OC-8 : A Chip-8 Emulator For OpenComputers (version 1.2)

local comp = require("component")
local ev = require("event")
local bit = require("bit32")
local fs = require("filesystem")
local gpu = comp.gpu
local shell = require("shell")
local unicode = require("unicode")
local computer = require("computer")

local b_and, b_shl, b_shr, b_xor, b_or = bit.band, bit.lshift, bit.rshift, bit.bxor, bit.bor
local floor, random = math.floor, math.random
local s_char, s_sub, s_lower = string.char, string.sub, string.lower
local os_clock = os.clock

-- Sound card detection
local hasSoundCard = comp.isAvailable("sound")
local sound = nil
local soundChannel = 1
local soundEnabled = true

if hasSoundCard then
    sound = comp.sound
    -- Initialize sound card
    sound.open(soundChannel)
    sound.setWave(soundChannel, sound.modes.square)
    sound.setVolume(soundChannel, 0.8)
    sound.setADSR(soundChannel, 1, 100, 0, 1)
    print("Sound card detected and initialized!")
else
    print("No sound card detected, using computer.beep() for audio")
end

local isTier1 = (gpu.maxDepth() == 1)

local hires = false
local shiftQuirk = true
local loadStoreQuirk = true
local screenW, screenH = gpu.getResolution()
local instructionsPerLoop = 150

local dotMap = {
  {0x1, 0x8},
  {0x2, 0x10},
  {0x4, 0x20},
  {0x40, 0x80}
}

local mem = {} for i=0,4095 do mem[i]=0 end
local V = {} for i=0,15 do V[i]=0 end
local RPL = {} for i=0,7 do RPL[i]=0 end
local stack = {}
local I, PC, SP = 0, 0x200, 0
local delayT, soundT = 0, 0
local soundActive = false
local keys = {}
local keyMap = "1234qwerasdfzxcv"
local keyPending, keyWaitReg, keyWaitAddr = nil, nil, nil

local disp, lastDispChar = {}, {}
local function clearScreen()
  for x=0,127 do
    disp[x] = disp[x] or {}
    for y=0,63 do disp[x][y] = false end
  end
  for i=1,screenW do lastDispChar[i] = {} end
  gpu.setBackground(0x000000)
  gpu.fill(1, 1, screenW, screenH, " ")
end

local function drawStatus()
  local status = string.format(" SPEED: %d Cycles/Loop | Arrows to Adjust | Sound: %s",
    instructionsPerLoop,
    (hasSoundCard and soundEnabled and "CARD" or (hasSoundCard and "MUTED" or "BEEP")))
  gpu.setForeground(0x000000)
  gpu.setBackground(0xFFFFFF)
  gpu.set(1, screenH, status .. string.rep(" ", screenW - #status))
  gpu.setBackground(0x000000)
  gpu.setForeground(0xFFFFFF)
end

-- Sound control functions
local function startSound()
  if not soundEnabled then return end
  if hasSoundCard then
    -- Use the sound card for better audio
    sound.setFrequency(soundChannel, 440) -- 440Hz is a good beep frequency
    sound.setVolume(soundChannel, 0.8)
    -- Re-open channel if needed
    sound.close(soundChannel)
    sound.open(soundChannel)
    sound.setWave(soundChannel, sound.modes.square)
    sound.setADSR(soundChannel, 1, 100, 0, 1)
    sound.delay(16) -- 16ms beep
    sound.process()
  else
    -- Fallback to computer.beep
    computer.beep(440, 0.016)
  end
end

local function stopSound()
  if hasSoundCard and soundEnabled then
    sound.setVolume(soundChannel, 0)
    sound.process()
  end
end

local function toggleSound()
  if hasSoundCard then
    soundEnabled = not soundEnabled
    if not soundEnabled then
      sound.setVolume(soundChannel, 0)
      sound.process()
    else
      sound.setVolume(soundChannel, 0.8)
    end
    drawStatus()
    return true
  end
  return false
end

local function draw()
  local curW = hires and 128 or 64
  local curH = hires and 64 or 32
  local charW = curW / 2
  local charH = curH / 4
  local offX = floor((screenW - charW) / 2)
  local offY = floor((screenH - charH) / 2)

  for py = 0, charH - 1 do
    for px = 0, charW - 1 do
      local charCode = 0x2800
      for dy = 0, 3 do
        for dx = 0, 1 do
          if disp[px * 2 + dx][py * 4 + dy] then
            charCode = charCode + dotMap[dy + 1][dx + 1]
          end
        end
      end
      local char = unicode.char(charCode)
      if (py + offY + 1) < screenH then
        if char ~= lastDispChar[px + offX][py + offY] then
          gpu.set(px + offX + 1, py + offY + 1, char)
          lastDispChar[px + offX][py + offY] = char
        end
      end
    end
  end
end

local function loadFonts()
  local fonts = {
    0xF0,0x90,0x90,0x90,0xF0, 0x20,0x60,0x20,0x20,0x70, 0xF0,0x10,0xF0,0x80,0xF0, 0xF0,0x10,0xF0,0x10,0xF0,
    0x90,0x90,0xF0,0x10,0x10, 0xF0,0x80,0xF0,0x10,0xF0, 0xF0,0x80,0xF0,0x90,0xF0, 0xF0,0x10,0x20,0x40,0x40,
    0xF0,0x90,0xF0,0x90,0xF0, 0xF0,0x90,0xF0,0x10,0xF0, 0xF0,0x90,0xF0,0x90,0x90, 0xE0,0x90,0xE0,0x90,0xE0,
    0xF0,0x80,0x80,0x80,0xF0, 0xE0,0x90,0x90,0x90,0xE0, 0xF0,0x80,0xF0,0x80,0xF0, 0xF0,0x80,0xF0,0x80,0x80,
    0xFF,0xFF,0xC3,0xC3,0xC3,0xC3,0xC3,0xC3,0xFF,0xFF, 0x18,0x38,0x78,0x18,0x18,0x18,0x18,0x18,0x7E,0x7E,
    0xFF,0xFF,0x03,0x03,0xFF,0xFF,0xC0,0xC0,0xFF,0xFF, 0xFF,0xFF,0x03,0x03,0xFF,0xFF,0x03,0x03,0xFF,0xFF,
    0xC3,0xC3,0xC3,0xC3,0xFF,0xFF,0x03,0x03,0x03,0x03, 0xFF,0xFF,0xC0,0xC0,0xFF,0xFF,0x03,0x03,0xFF,0xFF,
    0xFF,0xFF,0xC0,0xC0,0xFF,0xFF,0xC3,0xC3,0xFF,0xFF, 0xFF,0xFF,0x03,0x03,0x06,0x0C,0x18,0x18,0x18,0x18,
    0xFF,0xFF,0xC3,0xC3,0xFF,0xFF,0xC3,0xC3,0xFF,0xFF, 0xFF,0xFF,0xC3,0xC3,0xFF,0xFF,0x03,0x03,0xFF,0xFF,
    0x7E,0x7E,0xC3,0xC3,0xC3,0xFF,0xFF,0xC3,0xC3,0xC3, 0xFC,0xFC,0xC3,0xC3,0xFC,0xFC,0xC3,0xC3,0xFC,0xFC,
    0x3C,0x3C,0x60,0x60,0x60,0x60,0x60,0x60,0x3C,0x3C, 0xFC,0xFC,0xC3,0xC3,0xC3,0xC3,0xC3,0xC3,0xFC,0xFC,
    0xFF,0xFF,0xC0,0xC0,0xF8,0xF8,0xC0,0xC0,0xFF,0xFF, 0xFF,0xFF,0xC0,0xC0,0xF8,0xF8,0xC0,0xC0,0xC0,0xC0
  }
  for i=0,#fonts-1 do mem[i] = fonts[i+1] end
end

local function selectRom()
  local path = shell.getWorkingDirectory()
  local files = {}
  for f in fs.list(path) do if f:match("%.ch8$") then files[#files+1] = f end end
  if #files == 0 then print("No .ch8 files found!") return nil end

  gpu.setBackground(0x000000)
  gpu.setForeground(0xFFFFFF)
  gpu.fill(1,1,screenW,screenH," ")

  gpu.set(2, 2, "8\"\"\"88 8\"\"\"\"8       eeeee  8 ")
  gpu.set(2, 3, "8    8 8    \"       8   8  88")
  gpu.set(2, 4, "8    8 8e           8eee8  88")
  gpu.set(2, 5, "8    8 88     eeee 88   88 88")
  gpu.set(2, 6, "8    8 88   e      88   88   ")
  gpu.set(2, 7, "8eeee8 88eee8      88eee88 88")
  gpu.set(2, 8, "OC-8: CH8/SCH8 Emulator for OC by nonogamer9")

  if hasSoundCard then
    gpu.set(2, 9, "Sound Card: ENABLED (Press S to toggle)")
  else
    gpu.set(2, 9, "Sound: Using computer.beep() (no sound card detected)")
  end

  gpu.set(2, 10, "Select a ROM (1-"..#files.."):")
  for i, f in ipairs(files) do gpu.set(4, i+11, i..". "..f) end

  local choice = nil
  while true do
    local e = {ev.pull("key_down")}
    local n = tonumber(s_char(e[3]))
    if n and files[n] then choice = path.."/"..files[n] break end
    if e[4] == 28 then break end
  end
  return choice
end

local function step()
  if keyPending then return false end
  local op = b_or(b_shl(mem[PC], 8), mem[PC+1])
  PC = PC + 2
  local n1, x, y, n4 = b_shr(op, 12), b_and(b_shr(op, 8), 0xF), b_and(b_shr(op, 4), 0xF), b_and(op, 0xF)
  local nn, nnn = b_and(op, 0xFF), b_and(op, 0xFFF)

  if n1 == 0 then
    if op == 0x00E0 then clearScreen()
    elseif op == 0x00EE then PC = stack[SP] SP = SP - 1
    elseif op == 0x00FF then if not isTier1 then hires = true; clearScreen() end
    elseif op == 0x00FE then hires = false; clearScreen()
    elseif op == 0x00FD then
      -- Cleanup sound card on exit
      if hasSoundCard then
        sound.close(soundChannel)
      end
      os.exit()
    elseif op == 0x00FB then
      for sx=127,4,-1 do disp[sx] = disp[sx-4] end
      for sx=0,3 do disp[sx] = {}; for sy=0,63 do disp[sx][sy]=false end end
    elseif op == 0x00FC then
      for sx=0,123 do disp[sx] = disp[sx+4] end
      for sx=124,127 do disp[sx] = {}; for sy=0,63 do disp[sx][sy]=false end end
    elseif b_and(op, 0xFFF0) == 0x00C0 then
      local n = b_and(op, 0xF)
      for sx=0,127 do
        for sy=63,n,-1 do disp[sx][sy] = disp[sx][sy-n] end
        for sy=0,n-1 do disp[sx][sy] = false end
      end
    end
  elseif n1 == 1 then PC = nnn
  elseif n1 == 2 then SP = SP + 1; stack[SP] = PC; PC = nnn
  elseif n1 == 3 then if V[x] == nn then PC = PC + 2 end
  elseif n1 == 4 then if V[x] ~= nn then PC = PC + 2 end
  elseif n1 == 5 then if V[x] == V[y] then PC = PC + 2 end
  elseif n1 == 6 then V[x] = nn
  elseif n1 == 7 then V[x] = b_and(V[x] + nn, 0xFF)
  elseif n1 == 8 then
    if n4 == 0 then V[x] = V[y]
    elseif n4 == 1 then V[x] = b_or(V[x], V[y])
    elseif n4 == 2 then V[x] = b_and(V[x], V[y])
    elseif n4 == 3 then V[x] = b_xor(V[x], V[y])
    elseif n4 == 4 then local s = V[x]+V[y] V[x]=b_and(s,0xFF) V[15]=(s>0xFF) and 1 or 0
    elseif n4 == 5 then V[15]=(V[x]>=V[y]) and 1 or 0 V[x]=b_and(V[x]-V[y],0xFF)
    elseif n4 == 6 then
      if shiftQuirk then V[15]=b_and(V[x],1) V[x]=b_shr(V[x],1)
      else V[15]=b_and(V[y],1) V[x]=b_shr(V[y],1) end
    elseif n4 == 7 then V[15]=(V[y]>=V[x]) and 1 or 0 V[x]=b_and(V[y]-V[x],0xFF)
    elseif n4 == 14 then
      if shiftQuirk then V[15]=b_shr(V[x],7) V[x]=b_and(b_shl(V[x],1),0xFF)
      else V[15]=b_shr(V[y],7) V[x]=b_and(b_shl(V[y],1),0xFF) end
    end
  elseif n1 == 9 then if V[x] ~= V[y] then PC = PC + 2 end
  elseif n1 == 0xA then I = nnn
  elseif n1 == 0xB then PC = nnn + V[0]
  elseif n1 == 0xC then V[x] = b_and(random(0,255), nn)
  elseif n1 == 0xD then
    V[15] = 0
    local w, h = (n4 == 0 and 16 or 8), (n4 == 0 and 16 or n4)
    local limX, limY = (hires and 128 or 64), (hires and 64 or 32)
    for r=0, h-1 do
      local line = (n4 == 0) and b_or(b_shl(mem[I+r*2], 8), mem[I+r*2+1]) or mem[I+r]
      for c=0, w-1 do
        if b_and(line, b_shl(1, (w-1)-c)) ~= 0 then
          local tx, ty = b_and(V[x]+c, limX-1), b_and(V[y]+r, limY-1)
          if disp[tx][ty] then V[15] = 1 end
          disp[tx][ty] = not disp[tx][ty]
        end
      end
    end
    return true
  elseif n1 == 0xE then
    if nn == 0x9E then if keys[V[x]] then PC = PC + 2 end
    elseif nn == 0xA1 then if not keys[V[x]] then PC = PC + 2 end end
  elseif n1 == 0xF then
    if nn == 0x07 then V[x] = delayT
    elseif nn == 0x0A then keyPending, keyWaitReg, keyWaitAddr = true, x, PC
    elseif nn == 0x15 then delayT = V[x]
    elseif nn == 0x18 then
      soundT = V[x]
      -- Start sound immediately if sound timer is set
      if soundT > 0 and not soundActive then
        startSound()
        soundActive = true
      end
    elseif nn == 0x1E then I = b_and(I + V[x], 0xFFFF)
    elseif nn == 0x29 then I = V[x] * 5
    elseif nn == 0x30 then I = 80 + (V[x] * 10)
    elseif nn == 0x33 then mem[I]=floor(V[x]/100) mem[I+1]=floor((V[x]%100)/10) mem[I+2]=V[x]%10
    elseif nn == 0x55 then
      for i=0,x do mem[I+i]=V[i] end
      if not loadStoreQuirk then I = I + x + 1 end
    elseif nn == 0x65 then
      for i=0,x do V[i]=mem[I+i] end
      if not loadStoreQuirk then I = I + x + 1 end
    elseif nn == 0x75 then for i=0,math.min(x,7) do RPL[i]=V[i] end
    elseif nn == 0x85 then for i=0,math.min(x,7) do V[i]=RPL[i] end end
  end
  return false
end

loadFonts()
local romPath = selectRom()
if not romPath then return end

local f = io.open(romPath, "rb")
local d = f:read("*a")
f:close()
for i=1, #d do mem[0x200+i-1] = d:byte(i) end

clearScreen()
drawStatus()
local nextTimer = os_clock()

while true do
  local now = os_clock()
  while true do
    local ed = {ev.pull(0)}
    if not ed[1] then break end
    if ed[1] == "key_down" then
      local code = ed[4]
      local char = ed[3]
      local k = s_lower(s_char(char))

      -- Sound toggle with 'S' key
      if k == "s" and hasSoundCard then
        toggleSound()
      end

      if code == 200 then
        instructionsPerLoop = instructionsPerLoop + 25
        drawStatus()
      elseif code == 208 then
        instructionsPerLoop = math.max(1, instructionsPerLoop - 25)
        drawStatus()
      end
      for i=0,15 do if k == s_sub(keyMap, i+1, i+1) then
        keys[i] = true
        if keyPending then V[keyWaitReg], keyPending = i, nil end
      end end
    elseif ed[1] == "key_up" then
      local k = s_lower(s_char(ed[3]))
      for i=0,15 do if k == s_sub(keyMap, i+1, i+1) then keys[i] = false end end
    elseif ed[1] == "interrupted" then
      -- Cleanup on interrupt
      if hasSoundCard then
        sound.close(soundChannel)
      end
      return
    end
  end

  local redraw = false
  for _=1, instructionsPerLoop do if step() then redraw = true end end
  if redraw then draw() end

  if now >= nextTimer then
    if delayT > 0 then delayT = delayT - 1 end
    if soundT > 0 then
      soundT = soundT - 1
      if not soundActive then
        startSound()
        soundActive = true
      end
    else
      if soundActive then
        stopSound()
        soundActive = false
      end
    end
    nextTimer = now + 0.016
  end
end