Atari ST SAP player for CraftOS-PC sound plugin (requires https://gist.github.com/MCJack123/cf500b62fdbcb135d2db6cf97a771c6e)

sapplayer.lua

local M6502 = require "M6502"

local nsongs = 1
local defaultsong = 0
local stereo = false
local ntsc = false
local type = 0 -- 0 = B, 1 = C, 2 = D, 3 = S, 4 = R
local fastplay = 312
local initaddr = 0x0000
local musicaddr = 0x0000
local playeraddr = 0x0000
local duration = 0

local stwave = {}
do
    --local m = 0
    local sz = 256
    for i = 1, sz/4 do stwave[i] = -16*((i-1)/sz - 0.25)^2 end
    for i = sz/4+1, sz do stwave[i] = 0.05/((i-1)/sz - 0.2028) - 0.0625 end
    --for i = 1, #stwave do stwave[i] = math.min(math.max(stwave[i], -1), 1) end
end

term.clear()
term.setCursorPos(1, 1)
local win = window.create(term.current(), 41, 1, 10, 10)
win.clear()
local status = window.create(term.current(), 1, 1, 40, 19)
local oldterm = term.redirect(status)
pcall(function(...)
local mem = setmetatable({}, {__index = function() return 0 end})
local file = assert(fs.open(shell.resolve(...), "rb"))
if file.read(5) ~= "SAP\r\n" then file.close() error("Not a SAP file") end
while true do
    local s = file.read(2)
    if s == "\xFF\xFF" then break end
    repeat s = s .. file.read(1)
    until s:sub(-2, -1) == "\r\n"
    local cmd, par = s:match "^(%u+) ?(.*)\r\n"
    print(cmd, par)
    if cmd == "SONG" then nsongs = tonumber(par)
    elseif cmd == "DEFSONG" then defaultsong = tonumber(par)
    elseif cmd == "STEREO" then stereo = true
    elseif cmd == "NTSC" then ntsc, fastplay = true, 262
    elseif cmd == "TYPE" then
        if par == "B" then type = 0
        elseif par == "C" then type = 1
        elseif par == "D" then type = 2
        elseif par == "S" then type = 3
        elseif par == "R" then type = 4
        else file.close() error("Unknown TYPE") end
    elseif cmd == "FASTPLAY" then fastplay = tonumber(par)
    elseif cmd == "INIT" then initaddr = tonumber(par, 16)
    elseif cmd == "MUSIC" then musicaddr = tonumber(par, 16)
    elseif cmd == "PLAYER" then playeraddr = tonumber(par, 16)
    elseif cmd == "NAME" then --print("Title:", par:sub(2, -2))
    elseif cmd == "AUTHOR" then --print("Author:", par:sub(2, -2))
    elseif cmd == "DATE" then --print("Date:", par:sub(2, -2))
    end
end
while true do
    local s = file.read(2)
    if not s then break end
    local addr = ("<H"):unpack(s)
    if addr == 0xFFFF then addr = ("<H"):unpack(file.read(2)) end
    local e = ("<H"):unpack(file.read(2))
    for a = addr, e do mem[a] = file.read() end
end
file.close()

local cpu = M6502.new()
cpu:power(true)
local cpufreq = ntsc and 1789772.5 or 1773447
local pokey = {
    {lowfreq = false, hp24 = false, hp13 = false, div43 = false, div21 = false, c3hifreq = false, c1hifreq = false},
    {lowfreq = false, hp24 = false, hp13 = false, div43 = false, div21 = false, c3hifreq = false, c1hifreq = false}
}
for i = 1, stereo and 8 or 4 do
    sound.setVolume(i, 0)
    sound.setFrequency(i, 0)
    sound.setWaveType(i, "square", 0.5)
--    sound.setPan(i, stereo and (i > 4 and -1 or 1) or 0)
    if sound.version then sound.setInterpolation(i, "linear") end
end
local start = os.epoch "utc"
function cpu:read(addr)
    if bit32.band(addr, 0xFF0F) == 0xD40B then print("v") return math.floor((((os.epoch "utc" - start) / (ntsc and 16.666666 or 20)) % 1) * (ntsc and 130 or 155)) end
    if bit32.band(addr, 0xFF00) == 0xD200 then return mem[bit32.band(addr, stereo and 0xFF1F or 0xFF0F)] end
    if bit32.band(addr, 0xF800) == 0xD000 then return mem[bit32.band(addr, 0xFF0F)] end
    return mem[addr]
end
function cpu:write(addr, val)
    if bit32.band(addr, 0xFF00) == 0xD200 then
        local reg = bit32.band(addr, 0x000F)
        local chipsel = (stereo and bit32.btest(addr, 0x0010)) and 2 or 1
        mem[0xD200 + reg + ((chipsel-1) * 0x10)] = val -- technically not supposed to happen, but for safety in the emulator
        --print(reg, val)
        if reg == 8 then
            win.setCursorPos(1, 1)
            win.clearLine()
            win.write(("AUDCTL  %02X"):format(val))
            pokey[chipsel].lowfreq = bit32.btest(val, 0x01)
            pokey[chipsel].hp24 = bit32.btest(val, 0x02) if pokey[chipsel].hp24 then print("Unimplemented high-pass") end
            pokey[chipsel].hp13 = bit32.btest(val, 0x04) if pokey[chipsel].hp13 then print("Unimplemented high-pass") end
            pokey[chipsel].div43 = bit32.btest(val, 0x08)
            pokey[chipsel].div21 = bit32.btest(val, 0x10)
            pokey[chipsel].c3hifreq = bit32.btest(val, 0x20)
            pokey[chipsel].c1hifreq = bit32.btest(val, 0x40)
        elseif reg == 0xE then
            print("IRQ!")
        elseif reg < 8 then
            local channel = bit32.rshift(reg, 1) + ((stereo and bit32.btest(addr, 0x0010)) and 4 or 0) + 1
            if bit32.btest(addr, 1) then
                -- control
                win.setCursorPos(1, channel + 1)
                --win.clearLine()
                win.write(("%d %02X"):format(channel, val))
                local vol = bit32.band(val, 0x0F) / 15 / 2
                --print(channel, val)
                --sound.setVolume(channel + 8, bit32.band(val, 0x0F) / 150)
                local mode = bit32.band(val, 0xE0)
                local wt, arg = "none"
                if bit32.btest(val, 0x10) then wt, arg = "square", 1
                elseif mode == 0xA0 or mode == 0xE0 then wt, arg = "square", 0.5
                elseif mode == 0x20 then wt, arg = "triangle"
                elseif mode == 0xC0 then wt, arg, vol = sound.version and "custom" or "rsawtooth", stwave, vol * 2
                elseif mode == 0x80 then wt = "pnoise" end
                -- TODO: maybe implement other types (weird square-ish waves)
                if sound.getWaveType(channel) ~= wt then sound.setWaveType(channel, wt, arg) end
                --if channel == 1 then
                    sound.setVolume(channel, vol)
                --end
            else
                -- frequency
                local basefreq = (((channel % 4 == 1 and pokey[chipsel].c1hifreq) or (channel % 4 == 3 and pokey[chipsel].c3hifreq)) and cpufreq) or (pokey[chipsel].lowfreq and 15700 or 63921)
                if (pokey[chipsel].div43 and bit32.rshift(reg, 1) == 2) or (pokey[chipsel].div21 and bit32.rshift(reg, 1) == 0) then basefreq = sound.getFrequency(channel + 1) sound.setVolume(channel + 1, 0) end
                local freq
                if basefreq == cpufreq then freq = basefreq / (2 * (val + 4)) -- TODO: hifreq
                else freq = basefreq / (2 * (val + 1)) end
                --print(channel, freq)
                if freq >= 24000 then freq = 0 end
                win.setCursorPos(6, channel + 1)
                win.write(("% 5d"):format(freq))
                if sound.getWaveType(channel) == "custom" then freq = freq / 2^(35/12) end
                if sound.getFrequency(channel) ~= freq then sound.setFrequency(channel, freq) end
                --sound.setFrequency(channel + 8, freq)
            end
        end
    elseif addr == 0xD40A then print("punt!")
    else
        mem[addr] = val
    end
end

local song = tonumber(select(2, ...) or nil) or defaultsong
if type == 0 then
    print(("Initializing at %04X"):format(initaddr))
    cpu.state.a = song
    cpu:call(initaddr)
    print(("Playing at %04X"):format(playeraddr))
    local n = 0
    while true do
        local start = os.epoch "utc"
        cpu.state.pc = 0
        cpu:call(playeraddr, 114 * 20 * fastplay)
        if n % 100 == 0 then sleep(fastplay / (ntsc and 60*262 or 50*312))
        else while (os.epoch "utc" - start) / 1000 < fastplay / (ntsc and 60*262 or 50*312) do end end
        n = n + 1
    end
elseif type == 1 then
    print(("Initializing at %04X"):format(playeraddr + 3))
    cpu.state.a = 0x70
    cpu.state.x = bit32.rshift(musicaddr, 8)
    cpu.state.y = bit32.band(musicaddr, 0xFF)
    cpu:call(playeraddr + 3)
    cpu.state.a = 0
    cpu.state.x = song
    cpu:call(playeraddr + 3)
    print(("Playing at %04X"):format(playeraddr + 6))
    local n = 0
    while true do
        local start = os.epoch "utc"
        cpu.state.pc = 0
        cpu:call(playeraddr + 6, 114 * 20 * fastplay)
        if n % 100 == 0 then sleep(fastplay / (ntsc and 60*262 or 50*312))
        else while (os.epoch "utc" - start) / 1000 < fastplay / (ntsc and 60*262 or 50*312) do end end
        n = n + 1
    end
else error("Unimplemented TYPE " .. type) end

end, ...)
term.redirect(oldterm)