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3
Commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
 prosolis
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191f2b47bb |
Put the container on the chip, and find the held bus costs 463 times the seam
ROADMAP P6c, FINDINGS 68. 78,125 B of a DLXP2's audio out of channel 3, sample-exact, while the video channel fetches records off the same disc. The two pieces 67.6 said were missing: the lump buffer (pg_afill/pg_afetch, three slots and the minimum is unmeasured) and 67.2's remainder accumulator (pg_apay). The capture prices what the accumulator avoided at 1.26 s of lip-sync over the game, against 67.2's predicted 1.25. The finding is the third piece, which nothing had named: the MSM6258 has no starvation state, so the gap between a channel counting out and the next arm is a held nibble pair driving the predictor. Stealing, the seam is 0.51 ms over ten seconds because dma.i's new DM_HOOK services the chip from inside the transfer wait -- 250,000 of 250,240 looks. Held, the 68000 is halted and gets 369: every one of the ten lump boundaries has a seam, worst 72.8 ms, 2.31% of the audio. Identical bytes, different sound. 64.3 reaching the audio. Two bugs, and no counter in the player could see either. Clearing DM_BARV does not unchain a channel -- OCR bits 3-2 are what it obeys -- and the symptom is POLL TIMEOUT on the lump and every record after it. And the refill ran one lump ahead of its ring and overwrote the buffer the channel was reading: 11 of 11 armed, 11 fetched, no starve, and the sound wrong from 0.2 s in. Which is why the gate is a WAV: verify_packed_audio.py walks the stream one delivered byte at a time, because MAME's okim6258 resets the nibble select on every write and a byte is two nibbles only 99.994% of the time. check.sh ALL GREEN before (tmp/check_s36_start.log) and after (tmp/check_s36_end.log), with the new stage. Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6 |
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prosolis
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6dd3fb3597 |
Ask the chip which decoder it is, and find four wrong axes where one was expected
ROADMAP P6a, on the machine. 68000 code programs HD63450 channel 3 with the IPL ROM's own ADPCM bytes -- dual address, 8-bit port, cycle steal, external request -- and feeds the MSM6258 a designed 1,678-nibble stream at the chip's own pace: 839 B in 0.1074 s = 7,811.4 B/s against the format's 7,812.5, CER=$00. That transport is P6b's, not scaffolding. Sixteen candidate decoder models, three capture decimations and a searched prologue are fitted to MAME's capture. Exactly one reproduces it sample-exact over all 1,678 samples, and every axis carries a negative control: flip it alone and the closest survivor disagrees on 826, 1,504, 156 and 1,522 samples. The chip runs 'terms', takes the LOW nibble of a byte first, clamps the accumulator at 10 bits and starts it at -2. tools/encoder/adpcm.py defaulted to the opposite of all four, and 65.2 named the wrong axis as the risk: the delta formula is worth -2.88 dB and the NIBBLE ORDER is worth -25.74 dB. 65.1's "high first, measured" was a measurement of ffmpeg, i.e. of the VOX file convention, which is a different question from what a chip does with a byte in its data register. The 10-bit clamp is free on the Singe window and only because that window peaks at 435 of 511 -- 1.4 dB of headroom on a -13.4 dBFS passage, 12.1 dB below where the encoder was clamping, and inside the recursion. So the audio level is an open choice again, downward, and the loudest passage on the disc is unmeasured. Session 33's silence had two ordinary causes: the PPI's port C is an input until control word $92 says otherwise, and $01 is COMMAND_STOP. And a rig fact worth the space: the 8 MHz ADPCM clock is CT1 in the YM2151's $1B, delivered on the sound system's schedule rather than at the store, so a transfer started in the same breath as the setup plays its first ~17 ms at the old clock and no model fits a stream that changed rate part way through. Name the layer: this is MAME 0.277's okim6258 device model measured end to end through the machine's real transport. It settles the rig and not the silicon. Also struck: 64.4's "no MAME source tree is on this machine" -- there is none on disk, but the machine has network and the upstream tag fetches. check.sh ALL GREEN before (tmp/check_s34_start.log) and after (tmp/check_s34_end.log), with one new stage. Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6 |
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prosolis
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f925a1dd9a |
Put sound on the wire, and find three LSBs are worth 25 dB
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 |