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Commits
| Author | SHA1 | Message | Date | |
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 prosolis
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2f9f5cc995 |
Pace the ring, then read the DMAC config out of the IPL ROM: audio is cheap and the disk is not
Two sessions that were never separated in the working tree, so they land as one commit. check.sh ALL GREEN before and after both. SESSION 19 -- the ring rig gets a frame clock (FINDINGS 51). src/player/stream.s had no frame clock: it asked for record i the instant it finished i-1, outran any finite pipe, and never let the ring back up. The 49.1 sweep passing at 48 KB was therefore a wrap-correctness result and nothing else. PACE/PACEON ($18034/$18038) hold the decoder to 12 fps, so FR_HEAD-FR_TAIL finally means what it reads as: whole frames the decoder could still draw with delivery stopped dead. PACEON=0 free-runs and is what the wrap gate still uses, so every figure in 49 is unmoved. Paced, on the gate container: 64 KB holds 2 frames, 256 KB holds 7-8, 512 KB holds 14-15, all pixel-exact. Tolerance is ceiling-1, measured by cutting the pipe: 256 KB buys 500 ms of dead pipe, not 583. SLACK IS ACCUMULATED, NOT OWNED. It is built out of pipe-wire and a seek spends all of it. At 488 KB/s a 256 KB ring needs 4.83 s of play to reach its ceiling from empty; 512 KB needs 8.42 s to reach 14. A bigger ring raises the ceiling AND lengthens the climb, so a branch point does not ask "is the buffer big enough" but "has there been enough play since the last one" -- and Dragon's Lair's decision points are seconds apart. The rig now also says WHICH resource is binding: at 460 KB/s every ring from 192 KB to 512 KB is rate-bound at ceiling 4 and never fills, so larger rings are dead RAM in that scene. 20_seek_slack.py is the same model rewritten in Python from record sizes, sharing no code with the Lua producer: 35/35 ceilings inside its bracket. SESSION 20 -- the DMAC configuration was in the IPL ROM the whole time (FINDINGS 52). ROADMAP's "do this first" was to put the ADPCM stream on the bus. That needs a clocks-per-byte figure for the audio channel, and 11_cpu_budget.py was charging audio the DISK's rate -- 5 clk/B, its own help text calling it "single-address, bus held". Audio was being charged the favourable end of B3, a 242 KB/s open question. It never had to be a guess. The IPL ROM programs all four HD63450 channels itself and MAME boots the rig with it, so 21_iplrom_dmac.py reads the configuration out of the image and decodes the MC68450 fields. Eight (address, expected bytes, meaning) sites; a mismatch or an unknown revision exits non-zero. In check.sh, no emulator, milliseconds. ch3 DCR=$80, OCR=$32: dual address, 8-bit port, cycle steal WITHOUT hold, REQG=10 external request. The DMAC arbitrates once per byte with no burst to amortise the 5..8 + 2 over, so an audio byte is 16..19 clocks, not 5 -- the old debit was 3.2x..3.8x small. And on the bus it is still nothing: 651 B/frame is 1.25%..1.48% of a frame, about 4% of what the decoder leaves. P6's bus risk does not materialise. The unit worry was worth checking and nearly right: 15.6 kHz is 8 MHz/512 = 15,625 samples/s, two 4-bit samples to a byte = 7,812.5 B/s exactly, and AUDIO_KBPS=7.8 is that in decimal kB while the tool multiplied by 1024. THE DISK CHANNEL IS PROGRAMMED IDENTICALLY. ch1 (SASI) is DCR=$80 too, and so is ch0. That is 16..19 clocks per delivered byte, where 42.4 brackets W at 5..12 and 42.5 has W=8 already missing 47/120 frames. The only worked example of a disk DMA configuration on this machine sits above the entire bracket, and at that price nothing fits at any container size. It is not scsiexrom.bin so B3 stays open -- what changed is that a cheap configuration is now the thing that has to be SHOWN. W <= 12 is a requirement on the player's DMAC programming, not a range the hardware hands us, and it is now the largest open number in the project, ahead of the rate. An unforced cross-check fell out: 15_bus_occupancy.py's new W sweep puts W=8 at 105.7% of the frame, agreeing with 42.5's 47/120, from mode histograms and bus clocks respectively, two models sharing no code. Also: ADPCM outranks the disk at the arbiter (CPR 1 against 2), so an audio byte never waits and a video byte does -- relevant to 51's smooth-rate delivery model. README MEDIA. stream.lua gains DLX_SNAP_EVERY=1 (needs DLX_PACE, off by default, on no path check.sh takes) and tools/media/make_readme_media.py turns the PNGs into docs/img/. The stills and both clips are MAME's own screen pixels. Building it turned up something worth recording. 116 of 119 captured frames are pixel-exact against dlx.py; three are TORN -- frame n on top, frame n-1 below the tear line -- because MAME captured the screen while the block loop was partway down it. decode.s writes straight to the displayed page (one display path, 28.1), so a real player tears the same way, and this is the first time that consequence has been visible rather than argued. The script ASSERTS the tear and refuses to build otherwise, rather than trimming three frames and reporting "every frame I kept is exact". Second correction the capture forced: the snapshot fires before frame n is decoded, so the obvious reading is that it holds frame n-1 -- it does not, because MAME renders the screen at the end of the machine frame, by which time the 68000 has finished frame n. 11_cpu_budget.py's "validated to within 1 pt" line is also corrected: the model reads 2..10 pt HIGH and by more as the frame gets harder, which was already true before either session. src/player/decode.s is unchanged; decode.bin is still 1,296 B at the same MD5. Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6 |
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prosolis
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64cd1ffd72 |
Handoff: reconcile docs and tooling with the corrections made this session
Session 2 reversed several of its own conclusions. The docs are append-only, so a reader could land on a superseded section and act on it. This pass makes the repo internally consistent. Defects found and fixed in STATUS.md: - claimed "Hybrid VQ with k=1024: no" as the answer to the linework question, directly contradicting FINDINGS 14, which rejected k=1024. Both profiles are k=256. - malformed profile table (six column separators, five columns). - next-steps list had two items numbered 3 and listed the full-disc survey twice. - the disk-benchmark section still read CRITICAL-PATH with "if SCSI sustains >=800 KB/s, ship pixel-exact". That was written while the bandwidth figure was misread as 4 MB/s. At 4 Mbps pixel-exact needs 92-97% of the pipe and is not available, and the ring-buffer result means the design no longer hangs on the benchmark at all. Rewritten with what it IS still worth doing: confirming the 4 Mbps provenance, and confirming DMA is used rather than PIO. FINDINGS now carries supersession blockquotes on 5, 8, 11, 17 and 18 pointing at the sections that correct them. 18 is the dangerous one -- its peak-vs- sustained test is reversed by 21 -- so it is marked DO NOT ACT ON THIS SECTION while noting the per-frame data itself remains valid. profile_gen.py had the same problem in code: it defaulted to the superseded peak sizing and returned lam=25 where the docs say lam=10. The buffered test is now the default and peak sizing is behind --size-for-peak as a bound only. A tool that contradicts the findings is worse than no tool. Also preserves the five measurement scripts that produced this session's numbers as tools/analysis/05-09, following the session 1 precedent, and adds an "explicitly abandoned -- do not re-propose" list to STATUS covering entropy coding, k=1024 codebooks and flat 4x4 VQ. Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6 |
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prosolis
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48e912de8b |
Size against 4 Mbps: peaks break the scsi profile; DMA steal is not free
User clarified the bandwidth figure is 4 Mbps (488 KB/s), not 4 MB/s -- ~8x
tighter than the previous commit reasoned against. Two consequences, plus a
correction to session 1.
1. The scsi profile committed in
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