prosolis
f0f2f807a4
The profiles shipped in e4062ed were set far too low. 45 KB/s (sasi) and
75 KB/s (scsi) are 12% and 7% of the respective folklore bus figures. They had
been read off the knee of the rate-distortion curve and then presented as
though bandwidth-derived, which they were not.
Raised to sasi 110 KB/s (lam=60) and scsi 280 KB/s (lam=10) -- 35% and 28%
utilisation. scsi is now within 0.52 dB of the palette ceiling on scene 00020.
Checking the CPU side, which nobody had done for the decode path, produces a
second and more important result. Against the 833k cycle/frame budget at 12fps:
full-frame blit, every frame 319k 38% affordable
LZ4/LZSS decode ~30KB/frame 450k 54%
deflate decode ~30KB/frame 1800k 216% infeasible
So raising the VQ bitrate is nearly free -- RAW, the mode that dominates at
high rate, is the cheapest mode to blit -- but entropy coding is not viable at
all. That demotes the "247 KB/s lossless changed-spans+deflate" figure from
FINDINGS 8 to a compression upper bound rather than a shippable design, and
removes entropy coding from the roadmap. VQ is the right architecture precisely
because its decode is a table copy.
Also confirms the architecture unifies: the hybrid at lam=0 lands within 3% of
the purpose-built lossless coder, so there is no separate lossless path.
Consequence for planning: the blocked disk benchmark is now critical-path, not
optional. If SCSI sustains >=800 KB/s the correct scsi profile is lam=0 --
pixel-exact video at ~450 KB/s and 38% CPU. Whether this port ships transparent
or lossy on SCSI is waiting on one measurement.
Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6
Dragon's Lair — Sharp X68000 port
Porting Dragon's Lair to a stock X68000 (68000 @ 10MHz, 2MB, SASI/SCSI).
This is fundamentally a video codec problem, not a game-logic problem: the game logic is a scene table with branching input windows; the difficulty is pushing ~22 minutes of Don Bluth animation through a 10MHz 68000.
Read first
docs/FINDINGS.md— measured hardware facts, content statistics, codec decision, and a section on measurement traps that produced three separate false results. Read §4 before trusting any pipeline number.docs/STATUS.md— current state, working setup, blockers, next steps.docs/HARDWARE.md— X68000 GVRAM/CRTC reference.
Layout
docs/ findings, status, hardware reference
tools/analysis/ frame-analysis scripts (01/02 marked BROKEN as regression refs)
tools/bench/ MAME Lua injection harness + 68000 benchmark sources
tools/vasm/ vasm m68k assembler (built from source)
tools/encoder/ hybrid VQ encoder + DLX1 container writer (working)
src/player/ 68000 player (not yet written)
assets/ extracted frames/audio (gitignored)
Encoder
python3 tools/encoder/extract.py 00020 /tmp/fr 12 crop
python3 tools/encoder/encode.py /tmp/fr out.dlx --profile sasi --preview p.png
Two quality profiles ship from one codec and one decoder — sasi (45 KB/s) and
scsi (120 KB/s) are two points on the same rate-distortion curve. The codec is
a Cinepak-style hybrid: each 4x4 block is coded as SKIP, one 4x4 codeword, four
2x2 codewords, or RAW literal pixels, chosen per block by rate-distortion.
The RAW escape means lam=0 is pixel-exact against the palettised frame, so the
quality knob spans lossless to heavily-compressed without changing the bitstream.
Source media (DRAGONS_LAIR.iso) and ROMs are gitignored — supply your own.