prosolis
f925a1dd9a
ROADMAP P6, everything in the item except the bus half session 20 closed. tools/encoder/adpcm.py is an MSM6258 codec, tools/encoder/extract_audio.py takes the same seconds of the same stream the frames come from, tools/bench/verify_adpcm.py is the gate, tools/analysis/32_audio_wire.py the container arithmetic. There is no reference encoder -- ffmpeg has a decoder for this format and none the other way -- so what is gated is the decoder the encoder runs INSIDE its own nibble search, sample-exact against ffmpeg's over 4,268 nibbles. An encoder that agrees with its own wrong decoder is what that catches. The Singe window: 156,250 samples -> 78,125 B at 21.97 dB, which is 7,812.5 B/s to the byte. Normalising the disc's -13.4 dBFS level moves the SNR 21.97 -> 21.97, so the level is not a lever. And the two published delta formulas are not the same codec. They differ by at most 3 in 12-bit units; encode for one and decode on the other and the SNR goes 21.97 -> -2.88 dB, the noise louder than the signal, because ADPCM is recursive the way the video codec is temporally recursive. Which one the chip runs is now P6a and it is a precondition on shipping any audio. And audio is the first thing the packed branch's simplification has cost anything for. A record has no index BY DESIGN, so audio cannot be per-record without making records variable; it rides a fixed cadence (F, A), the obvious F=1 wastes 57.3% of every audio sector, and the pick is F=11 A=14 -- 0.09% padding, 14,336 B held, wire 582.0 -> 589.6 KB/s. The codec container, which kept its index, pays zero. The MAME experiment did not work and 65.5 says so: :okim6258 is there at $E92001/$E92003, read out of the machine's own program map, and feeding it from Lua recorded silence across control 0..3 x port C 0..15. The register semantics were not guessed at further. FINDINGS 65. check.sh ALL GREEN before and after, with a new stage. Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6
37 lines
1.5 KiB
Lua
37 lines
1.5 KiB
Lua
-- Feed the x68000's OWN okim6258 a known nibble stream and let MAME record what
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-- comes out, so that "which delta formula does the chip use" is a MEASUREMENT
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-- and not a reading of source code that is not on this machine (64.4).
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--
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-- The feed is deliberately SLOW -- a byte every host frame, where real time
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-- wants ~138 -- because the question is not the rate. A starved chip holds its
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-- last sample, so the wave is a STAIRCASE of the reconstructed values, which is
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-- exactly the sequence the two candidate formulas disagree about.
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M = manager.machine
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local sp = M.devices[":maincpu"].spaces["program"]
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local CTRL, DATA = 0xE92001, 0xE92003
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local CMD = tonumber(os.getenv("AD_CMD") or "1")
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-- 12 loud nibbles to climb the step index, then every nibble in turn: the pairs
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-- where the two formulas differ are all at step indices above the floor.
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local nibs = {}
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for i = 1, 12 do nibs[#nibs+1] = 7 end
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for i = 0, 15 do nibs[#nibs+1] = i end
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for i = 0, 15 do nibs[#nibs+1] = i end
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local bytes = {}
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for i = 1, #nibs, 2 do bytes[#bytes+1] = nibs[i] * 16 + nibs[i+1] end
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local n, started = 0, false
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SUB = emu.add_machine_frame_notifier(function()
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n = n + 1
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if n == 30 then
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sp:write_u8(CTRL, CMD)
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started = true
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print(string.format("[AD] ctrl $%02X written to $%06X", CMD, CTRL))
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elseif started and n > 30 and (n - 30) <= #bytes then
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sp:write_u8(DATA, bytes[n - 30])
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elseif started and (n - 30) == #bytes + 20 then
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print("[AD] fed " .. #bytes .. " bytes = " .. #nibs .. " nibbles")
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print("[AD] done")
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M:exit()
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end
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end)
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