USER DECISION: drop the `sasi` profile. Not on bandwidth -- on capacity. A SASI
volume is 40 MB, and the 22.8 min of unique scene footage on the source Blu-ray
(streams 00000-00201, measured, not recalled) is 146 MiB at the LOWEST rate this
codec makes -- more than the machine's whole 4-unit SASI space. `scsi` is the
only profile now. FINDINGS 32.
Then the user asked whether we were drawing the wrong conclusions about PIO vs
DMA, and we were, more broadly than the question implied. Every CPU figure in
FINDINGS 24-34 is scored against the full 833,333 cycles/frame with nothing
subtracted for moving the bitstream off disk. Debiting the HD63450 cycle-steal
at the long-standing 8 clk/word ESTIMATE, "1 frame of 120 misses" becomes 84 of
120, median 112.4%. PIO at the span rate is 99.8% of the machine. Spans buy
cycles by spending bandwidth and the bandwidth returns as steal, so 31.6's "fits
completely" becomes a worst frame of 114.3%. 10 fps absorbs it: median 93.7%,
1/120. FINDINGS 35. `11_cpu_budget.py` takes --io dma|pio|none, defaults to dma,
and warns if asked for none.
Also landed:
- item 1 done: the cost model checked against the 68000 on a cost-aware
container, -3.07% to +0.01%, whole-window mean -1.22%. FINDINGS 34.
- item 4 done: the container carries its own 4-byte record alignment (DLX2).
94/120 record starts were on odd addresses -- an address error, not a slow
read -- now 0/120 for 16 B/s. Re-encoding reproduces 31.1 exactly. FINDINGS 33.
- a `scsi` window does not fit the 2 MB machine the rig emulates (2.84 MB of
stream past a 0x200000 ceiling). The gate now verifies 80 of 120 frames and
SAYS so, and fails loudly when the pass does not complete, instead of
reporting a phantom 49,005-pixel diff. FINDINGS 36.
Three near-misses this session had one shape: an unobservable run nearly
produced a false finding. stdbuf -oL on any MAME job that prints progress -- a
file is block-buffered too, and a run that is merely finishing looks exactly
like one that is wedged.
check.sh ALL GREEN.
Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6
src/player/decode.s parses DLX1 and decodes straight into GVRAM. Verified
pixel-exact over a 120-frame sequential run of the worst sustained window on
the disc -- all four block modes, full temporal recursion, so the last frame
is only right if all 120 were. In check.sh.
It costs a mean of 81.7% of a 12fps frame budget, and 31% of frames exceed
100% (42% at scsi). CPU is now the binding constraint. FINDINGS 28.
Three things that were believed and are not true:
- The dual-display-path plan of FINDINGS 24.5/25.6 is incoherent. The compose
path needs a RAM copy of the previous reconstruction; the direct path's
selling point is that it keeps none. Mixing them shows stale pixels on 70 of
120 frames, worst frame 18.8% of the screen. Every coherent repair is dearer
than not mixing, and 24.5's two figures were both copies with no decode in
either, so there was never a crossover to find. One path ships, and the 96KB
reference frame is gone. tools/analysis/10_pathmix_drift.py keeps the
counterexample runnable; check.sh asserts it still reproduces.
- The four block modes do not cost the same. V1 300, V4 448, RAW 400 cycles
against the old model's flat 207.8. V4 is 25% of blocks and 50% of the
cycles, and the mode decision charges it bytes it does not charge cycles for.
tools/analysis/11_cpu_budget.py reproduces all four frames timed on the
68000 to within 1 point. Hand-derived timings agree to 0.5% on V1.
- The container is big-endian but not aligned. Variable-length records laid end
to end put frame 1's length field at an odd address, and move.l (a0)+ there
is an address error: frame 0 decoded perfectly and then vectored into the
IPL for 59 emulated seconds looking like a hang. Found by dumping PC, not by
reading the source.
Also: an all-V1 frame, the cheapest possible full redraw, is 110.5% of budget.
No mode assignment fits a scene cut at 12fps. That one needs a decision, not a
measurement.
Next: charge cycles in the mode decision and bisect against 833,333 per frame,
the way session 6 bisects lam against bytes -- but with no bucket, because a
late frame cannot be banked.
Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6
prosolis