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
This commit is contained in:
prosolis
+47
-6
@@ -174,22 +174,44 @@ def main():
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help="override the profile's bitrate CEILING. The profile "
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"is a rate point on a delivery medium; this is for "
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"asking what the codec does at another one -- e.g. "
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"the 488 KB/s bus figure the span analyses of "
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"FINDINGS 30/40 are scored against.")
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"a measured delivery rate. Do not reach for the "
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"retired 4 Mbps figure; FINDINGS 42.1.")
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ap.add_argument("--span-kbps", type=float, default=None,
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help="byte ceiling the SPAN pass may draw on, if it differs "
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"from the profile's. The profile is a quality rate "
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"point; the pipe is hardware. Bytes between the two "
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"buy a better picture if spent on lam and the 68000's "
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"deadline if spent on spans -- and nothing at all if "
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"left unspent (FINDINGS 41.2). 488 is the bus figure "
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"tools/analysis/14_dmac_chain.py scores against.")
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"left unspent (FINDINGS 41.2). Pass the pipe rate "
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"tools/analysis/14_dmac_chain.py is scored against.")
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ap.add_argument("--spans", choices=("off", "need", "all"), default="need",
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help="v7 literal spans (FINDINGS 40). `need` (default) "
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"spends container bytes on spans only where a frame "
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"misses the 68000's decode deadline; `all` spends "
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"every profitable byte, which is the model "
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"14_dmac_chain.py scores; `off` emits DLX2.")
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ap.add_argument("--disk-clk-byte", type=float, default=None,
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help="clocks the SCSI DMA steals per DELIVERED BYTE, "
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"charged against the same frame budget the decoder "
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"spends (FINDINGS 43). Default 5.0, the "
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"single-address floor; 9.0 is dual-address; 0 "
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"restores the pre-43 encoder, which priced a byte at "
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"nothing and reported deadlines it could not meet.")
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ap.add_argument("--joint-decide", action="store_true",
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help="let the per-block lagrangian see the disk debit too, "
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"pricing a payload byte at lam+mu*c instead of lam. "
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"The default is OFF because it MEASURES as a wash: "
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"same 1/120, 0.02 dB worse, and it trades 6,058 "
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"clocks of disk for 17,207 of block decode "
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"(FINDINGS 44)")
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ap.add_argument("--joint-bucket", action="store_true",
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help="cap what the leaky bucket may lend a frame at what "
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"its clock budget can still absorb, since a borrowed "
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"byte is DISK_CLK_BYTE borrowed clocks and there is "
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"no double buffer to repay them from (FINDINGS 43.5). "
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"Default OFF: measured, it is worth one frame of 120 "
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"at --spans need and a 2%% regression at --spans all "
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"(FINDINGS 44)")
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ap.add_argument("--no-cpu-fit", action="store_true",
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help="drop the per-frame 68000 decode ceiling (session 7 "
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"behaviour: 31%% of frames on hard content do not fit)")
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@@ -214,6 +236,10 @@ def main():
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# The CPU ceiling is hardware, not taste: without it 31%% of frames on the
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# worst sustained window do not decode in time on a stock 68000, and with
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# it that is one frame -- the intra frame -- for 0.26 dB. FINDINGS 31.
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if a.disk_clk_byte is not None:
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RC.DISK_CLK_BYTE = a.disk_clk_byte
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RC.JOINT_DECIDE = a.joint_decide
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RC.JOINT_BUCKET = a.joint_bucket
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cyc_budget = None if a.no_cpu_fit else RC.FRAME_CYCLES
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span_mode = None if (a.spans == "off" or not rc) else a.spans
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@@ -225,6 +251,13 @@ def main():
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print(f" CPU ceiling: " + (f"mu bisected per frame against "
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f"{RC.FRAME_CYCLES:,.0f} cycles (12fps, stock 68000)"
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if cyc_budget else "OFF (--no-cpu-fit)"))
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print(f" disk debit: {RC.DISK_CLK_BYTE:g} clocks per delivered byte, "
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f"charged INSIDE that ceiling (FINDINGS 43), and "
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+ ("SEEN by the mode decision at lam+mu*c (--joint-decide)"
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if RC.JOINT_DECIDE else "not seen by the mode decision, "
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"which measures as the better container (FINDINGS 44)")
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if RC.DISK_CLK_BYTE else
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" disk debit: 0 -- bytes priced at nothing (pre-FINDINGS-43)")
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else:
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print(f" target {prof['kbps']} KB/s, FIXED lam={lam} (no rate control)")
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print(f" k1={k1} k4={k4}, {_IDX_BYTES}-byte indices")
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@@ -305,11 +338,19 @@ def main():
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# moved into the span section rather than removed.
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cyc = (np.asarray(enc["cycles"]) if "cycles" in enc
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else np.array([H.cycles(mm) for mm in enc["modes"]]))
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pct = 100 * cyc / RC.FRAME_CYCLES
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# The frame's real cost is decode PLUS the bus the SCSI DMA steals to
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# deliver it. Reporting only `cyc` is what let session 13 print 0/120 for
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# a container no machine could have played (FINDINGS 43).
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disk = np.asarray(enc["sizes"], float) * RC.DISK_CLK_BYTE
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pct = 100 * (cyc + disk) / RC.FRAME_CYCLES
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miss = int((pct > 100).sum())
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print(f" non-SKIP blocks/frame: median {np.median(ns):.1f}% "
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f"p90 {np.percentile(ns, 90):.1f}% max {ns.max():.1f}%")
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print(f" decode cost: median {np.median(pct):.1f}% "
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dpct = 100 * disk / RC.FRAME_CYCLES
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print(f" disk debit: median {np.median(dpct):.1f}% "
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f"p90 {np.percentile(dpct, 90):.1f}% max {dpct.max():.1f}% "
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f"of the frame budget, at {RC.DISK_CLK_BYTE:g} clocks/byte")
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print(f" decode+disk: median {np.median(pct):.1f}% "
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f"p90 {np.percentile(pct, 90):.1f}% max {pct.max():.1f}% "
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f"of a {a.fps}fps frame")
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print(f" frames that do NOT decode in time: {miss}/{len(pct)} "
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