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
+2
-194
@@ -88,18 +88,8 @@ FPTR = $18010 ; -> first frame record
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SCR_N = $18014 ; frames remaining this pass
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SCR_END = $18018 ; expected end of the current payload
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CB1 = $20000 ; expanded 4x4 codebook
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CB4 = $22000 ; expanded 2x2 codebook
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include "src/player/geom.i"
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DST0 = $C08000 ; GVRAM + 32*1024 (first picture row)
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DSTE = $C38000 ; GVRAM + 224*1024 (one past last)
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BROW = 4096 ; bytes per block row (4 picture rows)
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ROWLEN = 512 ; bytes per block row of blocks (64 * 8)
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MODEB = 768 ; packed mode header, 3072 blocks * 2 bits
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SPCU = 12 ; bytes of code per COARSE span unit (24 px)
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SPCN = 11 ; coarse units: 11*24 = 264 px >= one row
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SPFU = 2 ; bytes of code per FINE span unit (2 px)
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SPFN = 11 ; fine units: 11*2 = 22 px > one coarse unit
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org $10000
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start:
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@@ -130,186 +120,4 @@ hold: bra.s hold
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desync: move.l #$EE,FLAG.l
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bra.s hold
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; ---------------------------------------------------------------- one block
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; \1 = right-shift needed to bring this block's 2 mode bits to bits 1-0.
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BLOCK macro
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move.b (a1),d0
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ifne \1
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lsr.b #\1,d0
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endc
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and.w #3,d0
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beq .sk\@ ; 00 SKIP -- the median block
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subq.w #1,d0
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beq .v1\@ ; 01 V1
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subq.w #1,d0
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bne .rw\@ ; 11 RAW, else 10 V4
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; -- V4: four 2x2 codewords, sub-block order TL TR BL BR (vq_hybrid.paint)
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moveq #0,d0
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move.b (a0)+,d0
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lsl.w #3,d0
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movem.l (a3,d0.w),d0-d1
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move.l d0,(a4)
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move.l d1,1024(a4)
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moveq #0,d0
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move.b (a0)+,d0
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lsl.w #3,d0
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movem.l (a3,d0.w),d0-d1
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move.l d0,4(a4)
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move.l d1,1028(a4)
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moveq #0,d0
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move.b (a0)+,d0
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lsl.w #3,d0
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movem.l (a3,d0.w),d0-d1
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move.l d0,2048(a4)
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move.l d1,3072(a4)
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moveq #0,d0
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move.b (a0)+,d0
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lsl.w #3,d0
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movem.l (a3,d0.w),d0-d1
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move.l d0,2052(a4)
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move.l d1,3076(a4)
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bra .sk\@
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; -- V1: one 4x4 codeword, 32 bytes, straight out of the expanded codebook
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.v1\@:
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moveq #0,d0
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move.b (a0)+,d0
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lsl.w #5,d0
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movem.l (a2,d0.w),d0-d7 ; EA is resolved before the load
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movem.l d0-d1,(a4)
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movem.l d2-d3,1024(a4)
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movem.l d4-d5,2048(a4)
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movem.l d6-d7,3072(a4)
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bra .sk\@
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; -- RAW: 16 literal palette indices. Two indices are assembled into one long
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; via swap, so each pair of pixels costs one write instead of two; the high
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; byte of each word is left as zero because the hardware discards it anyway.
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.rw\@:
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RAWPAIR 0
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RAWPAIR 4
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RAWPAIR 1024
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RAWPAIR 1028
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RAWPAIR 2048
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RAWPAIR 2052
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RAWPAIR 3072
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RAWPAIR 3076
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.sk\@:
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addq.l #8,a4
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endm
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RAWPAIR macro
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moveq #0,d0
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move.b (a0)+,d0
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swap d0
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move.b (a0)+,d0
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move.l d0,\1(a4)
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endm
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; ------------------------------------------------------- the span section
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; in: a0 = span section, a1 = mode header (preserved across the call)
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; out: a0 = one past the section, i.e. the block payload
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;
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; This is tools/bench/blit.s v7 verbatim, and deliberately so: the 66.0 clocks
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; per span + 9.143 per coarse pixel + 9.978 per fine pixel of FINDINGS 40 were
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; measured on exactly this instruction sequence, over thirteen span lengths, and
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; a "tidier" rewrite here would silently invalidate every span figure in
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; FINDINGS 39/40 and in tools/analysis/14_dmac_chain.py.
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;
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; The fine chain is entered by FALLING OUT of the coarse one, so a span with no
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; coarse units enters at v7cx with d0 already reloaded -- which is why the
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; coarse displacement for c=0 is SPCN*SPCU, one past the last coarse unit,
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; rather than a special case.
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paint_spans:
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move.w (a0)+,d7 ; spans in this frame
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subq.w #1,d7
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bmi spnone ; a frame may legitimately have none (the
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; chain is far past a short branch)
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move.l a1,-(sp) ; a1 is a payload register below
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spspan: move.l (a0)+,a2 ; absolute GVRAM destination
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move.w (a0)+,d0 ; (SPCN - coarse) * SPCU
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jmp spch(pc,d0.w)
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spch:
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movem.l (a0)+,d0-d6/a1/a3-a6
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movem.l d0-d6/a1/a3-a6,(a2)
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lea 48(a2),a2
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movem.l (a0)+,d0-d6/a1/a3-a6
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movem.l d0-d6/a1/a3-a6,(a2)
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lea 48(a2),a2
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movem.l (a0)+,d0-d6/a1/a3-a6
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movem.l d0-d6/a1/a3-a6,(a2)
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lea 48(a2),a2
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movem.l (a0)+,d0-d6/a1/a3-a6
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movem.l d0-d6/a1/a3-a6,(a2)
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lea 48(a2),a2
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movem.l (a0)+,d0-d6/a1/a3-a6
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movem.l d0-d6/a1/a3-a6,(a2)
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lea 48(a2),a2
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movem.l (a0)+,d0-d6/a1/a3-a6
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movem.l d0-d6/a1/a3-a6,(a2)
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lea 48(a2),a2
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movem.l (a0)+,d0-d6/a1/a3-a6
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movem.l d0-d6/a1/a3-a6,(a2)
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lea 48(a2),a2
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movem.l (a0)+,d0-d6/a1/a3-a6
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movem.l d0-d6/a1/a3-a6,(a2)
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lea 48(a2),a2
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movem.l (a0)+,d0-d6/a1/a3-a6
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movem.l d0-d6/a1/a3-a6,(a2)
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lea 48(a2),a2
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movem.l (a0)+,d0-d6/a1/a3-a6
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movem.l d0-d6/a1/a3-a6,(a2)
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lea 48(a2),a2
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movem.l (a0)+,d0-d6/a1/a3-a6
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movem.l d0-d6/a1/a3-a6,(a2)
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lea 48(a2),a2
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spcx: move.w (a0)+,d0 ; (SPFN - fine) * SPFU, from mid-stream
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jmp spfh(pc,d0.w)
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spfh:
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move.l (a0)+,(a2)+
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move.l (a0)+,(a2)+
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move.l (a0)+,(a2)+
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move.l (a0)+,(a2)+
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move.l (a0)+,(a2)+
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move.l (a0)+,(a2)+
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move.l (a0)+,(a2)+
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move.l (a0)+,(a2)+
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move.l (a0)+,(a2)+
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move.l (a0)+,(a2)+
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move.l (a0)+,(a2)+
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dbra d7,spspan
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move.l (sp)+,a1
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spnone: rts
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; ------------------------------------------------------------- one frame
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; in: a0 = payload, a1 = packed mode header
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; out: a0 = one past the last payload byte consumed
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decode_frame:
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lea CB1,a2
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lea CB4,a3
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lea DST0,a6
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rowloop:
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move.l a6,a4
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lea ROWLEN(a6),a5
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byteloop:
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tst.b (a1) ; four SKIPs in one test
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beq allskip
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BLOCK 6
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BLOCK 4
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BLOCK 2
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BLOCK 0
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addq.l #1,a1
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cmpa.l a5,a4
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bne byteloop
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bra rowdone
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allskip:
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addq.l #1,a1
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lea 32(a4),a4
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cmpa.l a5,a4
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bne byteloop
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rowdone:
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lea BROW(a6),a6
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cmpa.l #DSTE,a6
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bne rowloop
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rts
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include "src/player/frame.i"
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