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
