prosolis
145753c0bf
Session 5 handoff. The user has chosen rate control as the next session's work, so this reads ratectl.py properly before that session starts rather than discovering the problem mid-implementation. FINDINGS 26: encode_rate_controlled() is not sound. H.encode() is temporally recursive -- SKIP blocks copy the previous RECONSTRUCTION -- but rate control builds a ladder of independent whole-sequence encodes and picks each frame from whichever rung fits the budget. Frames then reference reconstructions the decoder never saw. Measured on the Singe window: 67 rung switches, 111 of 120 frames drift, worst frame 43.4% of pixels, reported PSNR overstated by 0.36 dB. It would have wired up cleanly and reported a plausible wrong answer. Two further defects in the same function: the lam ladder runs to 2e5, 250x past the FINDINGS 15 cliff, so a frame that only fits up there is destroyed rather than rate-controlled; and with 5 rungs only two are ever chosen, straddling the operating point by 7.5x. The docstring describes a per-frame binary search, which is the right design -- the implementation is a fixed ladder. The leaky bucket does work and should be kept: 109.1 KB/s against a 110 target. tools/analysis/09_ratectl_drift.py is the regression test and the acceptance criterion: it exits non-zero until zero frames drift. Also corrected the stale 38% blit figure in ratectl.py's profile commentary, which session 5 measured at 53.6% (FINDINGS 24), and recorded the pgrep -f self-kill trap again -- four times across three sessions now. check.sh ALL GREEN. Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6
77 lines
3.7 KiB
Markdown
77 lines
3.7 KiB
Markdown
# Dragon's Lair — Sharp X68000 port
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Porting Dragon's Lair to a stock X68000 (68000 @ 10MHz, 2MB, SASI/SCSI).
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This is fundamentally a **video codec problem**, not a game-logic problem: the
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game logic is a scene table with branching input windows; the difficulty is
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pushing ~22 minutes of Don Bluth animation through a 10MHz 68000.
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**Green-light check:** `./tools/bench/check.sh` (~40 s, needs the Blu-ray
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mounted) re-runs both display regression tests and prints `ALL GREEN`.
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## Read first
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- **`docs/FINDINGS.md`** — measured hardware facts, content statistics, codec
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decision, and a section on measurement traps that produced three separate
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false results. Read §4 before trusting any pipeline number.
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- **`docs/STATUS.md`** — current state, working setup, blockers, next steps.
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**Start here.** It also lists what has been explicitly abandoned, so old ideas
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do not get re-proposed.
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- **`docs/BENCHMARK.md`** — how to measure the storage subsystem, and why a
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bandwidth figure out of MAME would be meaningless.
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- **`docs/HARDWARE.md`** — X68000 GVRAM/CRTC reference.
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## Layout
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```
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docs/ findings, status, hardware reference
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tools/analysis/ measurement scripts, numbered in the order they were written
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(01/02 marked BROKEN deliberately, kept as regression refs).
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Run from the repo root — they import from tools/encoder/.
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07 finds the hottest sustained window in a stream; 08 renders
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source | decoded | block-mode map as .webm; 09 is a regression
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test for the rate-control desync (FINDINGS 26) and exits
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non-zero until it is fixed.
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tools/bench/ MAME Lua injection harness + 68000 benchmark sources.
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`check.sh` re-runs both display regression tests (~40 s).
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`blit.s`/`blit.lua` time the full-frame GVRAM blit on the
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68000 itself (FINDINGS 24) — not part of check.sh, because
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wall timings would make the green-light check host-sensitive.
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`crtc_mode.lua` is the single source of truth for CRTC R00-R08
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and R20 — do not write CRTC values anywhere else.
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tools/vasm/ vasm m68k assembler (built from source)
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tools/encoder/ hybrid VQ encoder + DLX1 container writer (working)
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src/player/ 68000 player (not yet written)
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assets/ extracted frames/audio (gitignored)
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```
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## Encoder
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```
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python3 tools/encoder/extract.py 00020 /tmp/fr 12 crop
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python3 tools/encoder/encode.py /tmp/fr out.dlx --profile sasi --preview p.png
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```
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Two quality profiles ship from one codec and one decoder — `sasi` (110 KB/s) and
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`scsi` (280 KB/s) are two points on the same rate-distortion curve. The codec is
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a Cinepak-style hybrid: each 4x4 block is coded as SKIP, one 4x4 codeword, four
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2x2 codewords, or RAW literal pixels, chosen per block by rate-distortion.
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The RAW escape means `lam=0` is pixel-exact against the palettised frame, so the
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quality knob spans lossless to heavily-compressed without changing the bitstream.
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Profiles are derived from a bandwidth figure, not chosen by eye:
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```
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python3 tools/encoder/profile_gen.py --bw-mbps 4 --name scsi
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```
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> **On reading `docs/FINDINGS.md`:** it is append-only and several later sections
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> overturn earlier ones. Superseded sections carry a blockquote at the top
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> pointing to the correction — heed those, especially 18 (reversed by 21).
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Source media (`DRAGONS_LAIR.iso`) and ROMs are gitignored — supply your own.
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**Not every large stream is game footage.** `00216` is the feature with a
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burned-in commentary picture-in-picture and `00215` is the commentary itself —
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the two largest files on the disc. The clean 9.4-minute animation is **`00223`**.
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See FINDINGS 25.1 before running any size-ranked survey.
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