-- Feed the x68000's OWN okim6258 a known nibble stream and let MAME record what
-- comes out, so that "which delta formula does the chip use" is a MEASUREMENT
-- and not a reading of source code that is not on this machine (64.4).
--
-- The feed is deliberately SLOW -- a byte every host frame, where real time
-- wants ~138 -- because the question is not the rate. A starved chip holds its
-- last sample, so the wave is a STAIRCASE of the reconstructed values, which is
-- exactly the sequence the two candidate formulas disagree about.
M = manager.machine
local sp = M.devices[":maincpu"].spaces["program"]
local CTRL, DATA = 0xE92001, 0xE92003
local CMD = tonumber(os.getenv("AD_CMD") or "1")
-- 12 loud nibbles to climb the step index, then every nibble in turn: the pairs
-- where the two formulas differ are all at step indices above the floor.
local nibs = {}
for i = 1, 12 do nibs[#nibs+1] = 7 end
for i = 0, 15 do nibs[#nibs+1] = i end
for i = 0, 15 do nibs[#nibs+1] = i end
local bytes = {}
for i = 1, #nibs, 2 do bytes[#bytes+1] = nibs[i] * 16 + nibs[i+1] end

local n, started = 0, false
SUB = emu.add_machine_frame_notifier(function()
  n = n + 1
  if n == 30 then
    sp:write_u8(CTRL, CMD)
    started = true
    print(string.format("[AD] ctrl $%02X written to $%06X", CMD, CTRL))
  elseif started and n > 30 and (n - 30) <= #bytes then
    sp:write_u8(DATA, bytes[n - 30])
  elseif started and (n - 30) == #bytes + 20 then
    print("[AD] fed " .. #bytes .. " bytes = " .. #nibs .. " nibbles")
    print("[AD] done")
    M:exit()
  end
end)