Chip8 Emulator by Gamax92

local function pad(str, tolen) return string.rep("0", math.max(tolen - str:len(),0)) .. str end
local function binary(num)
    local bin = {}
    num = math.floor(num)
    repeat
    table.insert(bin, num%2)
    num = math.floor(num/2)
    until num == 0
    return table.concat(bin):reverse()
end
local tArgs = { ... }
if #tArgs < 2 then
    print("Usage: chip8 <rom> <side> [debug]")
    return
end

local rFile = shell.resolve(tArgs[1])
local eSide = tArgs[2]
local mDebug = not (tArgs[3] == nil)

if mDebug then print("Checking if rom exists ...") end
if not fs.exists(rFile) then
    print("Rom file " .. rFile .. " does not exist.")
    return
end
if mDebug then print("Checking if rom is a directory ...") end
if fs.isDir(rFile) then
    print("Rom file " .. rFile .. " is a directory.")
    return
end
if mDebug then print("Checking if side is monitor ...") end
if not peripheral.getType(eSide) == "monitor" then
    print("Peripheral on side " .. eSide .. " is not a monitor.")
    return
end
if mDebug then print("Attempting to wrap monitor ...") end
local mon = peripheral.wrap(eSide)
if mon == nil then
    print("Failed to wrap monitor on side " .. eSide)
    return
end
mon.setTextScale(0.5)
mon.clear()
local w,h = mon.getSize()
if mDebug then print("Checking if monitor is big enough ...") end
if w < 64 or h < 32 then
    print("The monitor on side " .. eSide .. " is too small.")
    print("Expected 64x32+\nGot " .. tostring(w) .. "x" .. tostring(h))
    return
end
if mDebug then print("Protection passed!\n") end

local chip8_keystate = {}
local chip8_keytrans = {}
local chip8_display = {}
for i = 0,63,1 do
    chip8_display[i] = {}
    for j = 0,31,1 do
        chip8_display[i][j] = 0
    end
end
local chip8_memory = {}
for i = 0, 4095, 1 do chip8_memory[i] = 0 end
local chip8_register = {}
for i = 0, 15, 1 do chip8_register[i] = 0 end
chip8_register["I"] = 512
chip8_register["PC"] = 512
chip8_register["DC"] = 0
chip8_register["SC"] = 0
local chip8_stack = {}
chip8_stack[0] = 0
local chip8_skip = 2
chip8_fontset = {
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}
print("Loading fontset ...")
for i = 1,80,1 do
    chip8_memory[i-1] = chip8_fontset[i]
end

chip8_keystate["0"] = 0
chip8_keystate["1"] = 0
chip8_keystate["2"] = 0
chip8_keystate["3"] = 0
chip8_keystate["4"] = 0
chip8_keystate["5"] = 0
chip8_keystate["6"] = 0
chip8_keystate["7"] = 0
chip8_keystate["8"] = 0
chip8_keystate["9"] = 0
chip8_keystate["A"] = 0
chip8_keystate["B"] = 0
chip8_keystate["C"] = 0
chip8_keystate["D"] = 0
chip8_keystate["E"] = 0
chip8_keystate["F"] = 0
chip8_keystate["END"] = 0

chip8_keytrans[45] = "0"
chip8_keytrans[2] = "1"
chip8_keytrans[3] = "2"
chip8_keytrans[4] = "3"
chip8_keytrans[16] = "4"
chip8_keytrans[17] = "5"
chip8_keytrans[18] = "6"
chip8_keytrans[30] = "7"
chip8_keytrans[31] = "8"
chip8_keytrans[32] = "9"
chip8_keytrans[44] = "A"
chip8_keytrans[46] = "B"
chip8_keytrans[5] = "C"
chip8_keytrans[19] = "D"
chip8_keytrans[33] = "E"
chip8_keytrans[47] = "F"
chip8_keytrans[59] = "END"

function chip8_loadrom()
    local rRom = fs.open(rFile,"rb")
    local index = 512
    local size = 0
    while true do
        byte = rRom.read()
        if byte == nil then break end
        chip8_memory[index] = byte
        index = index + 1
        size = size + 1
    end
    rRom.close()
    return size
end

function chip8_updatekeys()
    for i = 48,57,1 do
        chip8_keystate[string.char(i)] = chip8_keystate[string.char(i)] - 1
        if chip8_keystate[string.char(i)] < 0 then chip8_keystate[string.char(i)] = 0 end
    end
    for i = 65,70,1 do
        chip8_keystate[string.char(i)] = chip8_keystate[string.char(i)] - 1
        if chip8_keystate[string.char(i)] < 0 then chip8_keystate[string.char(i)] = 0 end
    end
    os.queueEvent("key","","done")
    while true do
        event,param1,param2 = os.pullEvent("key")
        if param2 == "done" then break end
        if not (chip8_keytrans[param1] == nil) then
            chip8_keystate[chip8_keytrans[param1]] = 4
            if mDebug then print("Pressed " .. chip8_keytrans[param1]) end
        end
    end
    return
end

function chip8_keywait()
    while true do
        for i = 48,57,1 do
            chip8_keystate[string.char(i)] = chip8_keystate[string.char(i)] - 1
            if chip8_keystate[string.char(i)] < 0 then chip8_keystate[string.char(i)] = 0 end
        end
        for i = 65,70,1 do
            chip8_keystate[string.char(i)] = chip8_keystate[string.char(i)] - 1
            if chip8_keystate[string.char(i)] < 0 then chip8_keystate[string.char(i)] = 0 end
        end
        os.queueEvent("key","","done")
        while true do
            event,param1,param2 = os.pullEvent("key")
            if param2 == "done" then break end
            if not (chip8_keytrans[param1] == nil) then
                chip8_keystate[chip8_keytrans[param1]] = 4
                if mDebug then print("Pressed " .. chip8_keytrans[param1]) end
                return tonumber(chip8_keytrans[param1],16)
            end
        end
        if pressed then break end
        sleep(0)
    end
end

function chip8_getkey(key)
    return chip8_keystate[key] > 0
end

function chip8_emulatecode()
    local l
    local opcode = pad(string.format("%X",chip8_memory[chip8_register["PC"]]),2) .. pad(string.format("%X",chip8_memory[chip8_register["PC"]+1]),2)
    local opcfst = string.sub(opcode,1,1)
    if mDebug then
        print("PC:" .. pad(string.format("%X",chip8_register["PC"]),4) .. "|I:" .. pad(string.format("%X",chip8_register["I"]),4) .. " - " .. opcode)
        curX,curY = term.getCursorPos()
        for i = 0,15,1 do
            term.setCursorPos(46,i+2) print("V" .. pad(string.format("%X",i),1) .. ":" .. pad(string.format("%X",chip8_register[i]),2))
        end
        term.setCursorPos(curX,curY)
    end
    for i = 0,15,1 do
        if chip8_register[i] > 255 then error("ERR1") end
        if chip8_register[i] < 0 then error("ERR2") end
    end
    chip8_register["PC"] = chip8_register["PC"] + 2
    if opcfst == "0" then
        if string.sub(opcode,2,4) == "0E0" then
            mon.clear()
            mon.setCursorPos(1,1)
            for i = 0,63,1 do
                for j = 0,31,1 do
                    chip8_display[i][j] = 0
                end
            end
        elseif string.sub(opcode,2,4) == "0EE" then
            chip8_register["PC"] = chip8_stack[chip8_stack[0]]
            chip8_stack[0] = chip8_stack[0] - 1
        end
    elseif opcfst == "1" then
        chip8_register["PC"] = tonumber(string.sub(opcode,2,4),16)
    elseif opcfst == "2" then
        chip8_stack[0] = chip8_stack[0] + 1
        chip8_stack[chip8_stack[0]] = chip8_register["PC"]
        chip8_register["PC"] = tonumber(string.sub(opcode,2,4),16)
    elseif opcfst == "3" then
        if chip8_register[tonumber(string.sub(opcode,2,2),16)] == tonumber(string.sub(opcode,3,4),16) then
            chip8_register["PC"] = chip8_register["PC"] + 2
        end
    elseif opcfst == "4" then
        if chip8_register[tonumber(string.sub(opcode,2,2),16)] ~= tonumber(string.sub(opcode,3,4),16) then
            chip8_register["PC"] = chip8_register["PC"] + 2
        end
    elseif opcfst == "5" then
        if chip8_register[tonumber(string.sub(opcode,2,2),16)] == chip8_register[tonumber(string.sub(opcode,3,3),16)] then
            chip8_register["PC"] = chip8_register["PC"] + 2
        end
    elseif opcfst == "6" then
        chip8_register[tonumber(string.sub(opcode,2,2),16)] = tonumber(string.sub(opcode,3,4),16)
    elseif opcfst == "7" then
        chip8_register[tonumber(string.sub(opcode,2,2),16)] = math.fmod(chip8_register[tonumber(string.sub(opcode,2,2),16)] + tonumber(string.sub(opcode,3,4),16),255)
    elseif opcfst == "8" then
        if string.sub(opcode,4,4) == "0" then
            chip8_register[tonumber(string.sub(opcode,2,2),16)] = chip8_register[tonumber(string.sub(opcode,3,3),16)]
        elseif string.sub(opcode,4,4) == "1" then
            chip8_register[tonumber(string.sub(opcode,2,2),16)] = bit.bor(chip8_register[tonumber(string.sub(opcode,2,2),16)],chip8_register[tonumber(string.sub(opcode,3,3),16)])
        elseif string.sub(opcode,4,4) == "2" then
            chip8_register[tonumber(string.sub(opcode,2,2),16)] = bit.band(chip8_register[tonumber(string.sub(opcode,2,2),16)],chip8_register[tonumber(string.sub(opcode,3,3),16)])
        elseif string.sub(opcode,4,4) == "3" then
            chip8_register[tonumber(string.sub(opcode,2,2),16)] = bit.bxor(chip8_register[tonumber(string.sub(opcode,2,2),16)],chip8_register[tonumber(string.sub(opcode,3,3),16)])
        elseif string.sub(opcode,4,4) == "4" then
            chip8_register[15] = 0
            chip8_register[tonumber(string.sub(opcode,2,2),16)] = chip8_register[tonumber(string.sub(opcode,2,2),16)] + chip8_register[tonumber(string.sub(opcode,3,3),16)]
            if chip8_register[tonumber(string.sub(opcode,2,2),16)] > 255 then
                chip8_register[15] = 1
                chip8_register[tonumber(string.sub(opcode,2,2),16)] = math.fmod(chip8_register[tonumber(string.sub(opcode,2,2),16)],256)
            end
        elseif string.sub(opcode,4,4) == "5" then
            chip8_register[15] = 1
            chip8_register[tonumber(string.sub(opcode,2,2),16)] = chip8_register[tonumber(string.sub(opcode,2,2),16)] - chip8_register[tonumber(string.sub(opcode,3,3),16)]
            if chip8_register[tonumber(string.sub(opcode,2,2),16)] < 0 then
                chip8_register[15] = 0
                chip8_register[tonumber(string.sub(opcode,2,2),16)] = chip8_register[tonumber(string.sub(opcode,2,2),16)] + 256
            end
        elseif string.sub(opcode,4,4) == "6" then
            chip8_register[15] = math.fmod(chip8_register[tonumber(string.sub(opcode,3,3),16)],2)
            chip8_register[tonumber(string.sub(opcode,2,2),16)] = bit.brshift(chip8_register[tonumber(string.sub(opcode,3,3),16)],1)
        elseif string.sub(opcode,4,4) == "7" then
            chip8_register[15] = 1
            chip8_register[tonumber(string.sub(opcode,2,2),16)] = chip8_register[tonumber(string.sub(opcode,3,3),16)] - chip8_register[tonumber(string.sub(opcode,2,2),16)]
            if chip8_register[tonumber(string.sub(opcode,2,2),16)] < 0 then
                chip8_register[15] = 0
                chip8_register[tonumber(string.sub(opcode,2,2),16)] = chip8_register[tonumber(string.sub(opcode,2,2),16)] + 256
            end
        elseif string.sub(opcode,4,4) == "E" then
            chip8_register[15] = math.floor(chip8_register[tonumber(string.sub(opcode,3,3),16)] / 128)
            chip8_register[tonumber(string.sub(opcode,2,2),16)] = math.fmod(bit.blshift(chip8_register[tonumber(string.sub(opcode,3,3),16)],1),256)
        end
    elseif opcfst == "9" then
        if not (chip8_register[tonumber(string.sub(opcode,2,2),16)] == chip8_register[tonumber(string.sub(opcode,3,3),16)]) then
            chip8_register["PC"] = chip8_register["PC"] + 2
        end
    elseif opcfst == "A" then
        chip8_register["I"] = tonumber(string.sub(opcode,2,4),16)
    elseif opcfst == "B" then
        chip8_register["PC"] = tonumber(string.sub(opcode,2,4),16) + chip8_register[0]
    elseif opcfst == "C" then
        chip8_register[tonumber(string.sub(opcode,2,2),16)] = bit.band(math.random(0,255),tonumber(string.sub(opcode,3,4),16))
    elseif opcfst == "D" then
        chip8_register[15] = 0
        local x = chip8_register[tonumber(string.sub(opcode,2,2),16)]
        local y = chip8_register[tonumber(string.sub(opcode,3,3),16)]
        local h = tonumber(string.sub(opcode,4,4),16)
        local dLine = ""
        local s = ""
        for i = 0,h-1,1 do
            dLine = ""
            s = pad(binary(chip8_memory[chip8_register["I"]+i]),8)
            for d = 0,7,1 do dLine = dLine .. tostring(chip8_display[math.fmod(x+d,64)][math.min(y+i,31)]) end
            line = pad(binary(bit.bxor(tonumber(s,2),tonumber(dLine,2))),8)
            for p = 1,8,1 do
                if not (x+p-1 > 63 or y+i > 31) then
                    mon.setCursorPos(x+p,y+i+1)
                    if string.sub(line,p,p) == "1" then
                        mon.setBackgroundColor(1)
                        mon.write("#")
                        mon.setBackgroundColor(32768)
                        chip8_display[math.fmod(x+p-1,64)][y+i] = 1
                    else
                        mon.write(" ")
                        if chip8_display[math.fmod(x+p-1,64)][y+i] == 1 then chip8_register[15] = 1 end
                        chip8_display[math.fmod(x+p-1,64)][y+i] = 0
                    end
                end
            end
        end
        if not mDebug then chip8_updatedisplay() end
    elseif opcfst == "E" then
        if string.sub(opcode,3,4) == "9E" then
            if chip8_getkey(string.format("%X",chip8_register[tonumber(string.sub(opcode,2,2),16)])) then
                chip8_register["PC"] = chip8_register["PC"] + 2
            end
        elseif string.sub(opcode,3,4) == "A1" then
            if not (chip8_getkey(string.format("%X",chip8_register[tonumber(string.sub(opcode,2,2),16)]))) then
                chip8_register["PC"] = chip8_register["PC"] + 2
            end
        end
    elseif opcfst == "F" then
        if string.sub(opcode,3,4) == "07" then
            chip8_register[tonumber(string.sub(opcode,2,2),16)] = chip8_register["DC"]
        elseif string.sub(opcode,3,4) == "0A" then
            chip8_register[tonumber(string.sub(opcode,2,2),16)] = chip8_keywait()
        elseif string.sub(opcode,3,4) == "15" then
            chip8_register["DC"] = chip8_register[tonumber(string.sub(opcode,2,2),16)]
        elseif string.sub(opcode,3,4) == "18" then
            chip8_register["SC"] = chip8_register[tonumber(string.sub(opcode,2,2),16)]
        elseif string.sub(opcode,3,4) == "1E" then
            chip8_register[15] = 0
            chip8_register["I"] = chip8_register["I"] + chip8_register[tonumber(string.sub(opcode,2,2),16)]
            if chip8_register["I"] > 4095 then
                chip8_register[15] = 1
                chip8_register["I"] = math.fmod(chip8_register["I"],256)
            end
        elseif string.sub(opcode,3,4) == "29" then
            chip8_register["I"] = chip8_register[tonumber(string.sub(opcode,2,2),16)] * 5
        elseif string.sub(opcode,3,4) == "33" then
            local bcd = pad(tostring(chip8_register[tonumber(string.sub(opcode,2,2),16)]),3)
            chip8_memory[chip8_register["I"]] = tonumber(string.sub(bcd,1,1))
            chip8_memory[chip8_register["I"]+1] = tonumber(string.sub(bcd,2,2))
            chip8_memory[chip8_register["I"]+2] = tonumber(string.sub(bcd,3,3))
        elseif string.sub(opcode,3,4) == "55" then
            for i = 0,tonumber(string.sub(opcode,2,2),16),1 do
                chip8_memory[chip8_register["I"]+i] = chip8_register[i]
            end
            chip8_register["I"] = chip8_register["I"] + tonumber(string.sub(opcode,2,2),16) + 1
        elseif string.sub(opcode,3,4) == "65" then
            for i = 0,tonumber(string.sub(opcode,2,2),16),1 do
                chip8_register[i] = chip8_memory[chip8_register["I"]+i]
            end
            chip8_register["I"] = chip8_register["I"] + tonumber(string.sub(opcode,2,2),16) + 1
        end
    end
    return
end

function chip8_updatedisplay()
    term.clear()
    for y = 0,31,1 do
        for x = 0,63,1 do
            term.setCursorPos(x*(50/64)+1,y*(18/32)+1)
            if chip8_display[x][y] == 1 then
                term.setBackgroundColor(1)
                term.write("#")
                term.setBackgroundColor(32768)
            end
        end
    end
    return
end

function chip8_delay()
    if chip8_register["DC"] > 0 then chip8_register["DC"] = chip8_register["DC"] - 1 end
    if chip8_register["SC"] > 0 then chip8_register["SC"] = chip8_register["SC"] - 1 end
--    chip8_skip = chip8_skip - 1
--    if chip8_skip == 0 then sleep(0.05) chip8_skip = 3 end
    return
end

print("Loading rom into memory ...")
size = chip8_loadrom()
print("Loaded " .. tostring(size) .. " bytes!")

print("Starting emulation, press F1 to end ...")
if not mDebug then sleep(1.5) term.clear() end

while true do
    chip8_updatekeys()
    if chip8_getkey("END") then break end
    chip8_emulatecode()
    chip8_delay()
end

print("Emulation ended.")
return