thejayman77
ba74bbd5aa
Per-vertex GS fog end-to-end (gs_stub emit incl. persp_emit5, gs_prim_list_feeder XYZ2->XYZF2 on PRIM.FGE, gs_make_sh3_scheduler_fixture.py F/FGE packing), new fog TBs, fidelity attribution tooling. Functional baseline before removing the dead bilinear lerp8 clamps (Codex: 161-node comb loop -> -0.042ns setup fail). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
95 lines
4.5 KiB
Markdown
95 lines
4.5 KiB
Markdown
# Ch435 — FRAME.FBMSK light-buffer alpha
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## Root cause
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The Ch434 current-frame light chain was structurally correct but the second
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draw of the CT32 conversion stage, draw 195973, has
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`FRAME.FBMSK=0xff000000`. The scheduler previously discarded that field when
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relocating the framebuffer, and the external LPDDR color path had no byte-mask
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transport. Draw 195973 therefore replaced alpha across the full 256x256
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target instead of preserving the alpha produced by draw 195957. Feeding that
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incorrect all-128 alpha target through the remaining ping-pong passes made the
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integrated frame much too dark.
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## Static fidelity result
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The first correction was an asset-boundary reconstruction. It retained alpha
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128 on the 20,861 lit texels and alpha zero on the 44,675 black texels, then
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propagated that target through draws 196087, 196108, 196129, 196167, and
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196177. The resulting 311-epoch `zsrt139f52` replay passed production
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simulation and the DE25-Nano runtime gates with zero drops, overflows, AXI
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errors, Z mismatches, or color mismatches.
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The board framebuffer is byte-identical to simulation at SHA-256
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`d0047677371a0f6e4e319458926f604a8599c92baaf34d09b8e1fd452e31662b`.
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Its mapped mean RGB `(26.38, 23.32, 21.19)` is close to the PCSX2 frame mean
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`(28.47, 23.54, 21.33)`, and the booth, lamp, rabbit, bench, and character are
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all readable. This supersedes the over-dark f49 result and is the live HDMI
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asset baseline. The remaining dominant visual defect is spatial speckle and
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edge noise, not global brightness.
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## Native RTL repair
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The production path now carries a four-bit byte enable derived from
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`FRAME.FBMSK` with each fragment:
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- the fixture generator preserves the captured upper 32 FRAME bits and
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rejects masks that are not byte-granular;
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- the raster wrapper converts each `00` mask byte to an enabled write byte and
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each `ff` byte to a preserved destination byte;
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- the request FIFO and color-align RAM carry the byte enable across the GS to
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EMIF path;
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- partial opaque writes use the same ordered destination-read/modify/write
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path as alpha blends;
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- the color stage merges disabled bytes from the destination after either the
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GS ALPHA equation or opaque source selection.
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The directed color-blend regression preserves destination alpha with
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`BE=0111`, producing `0x8024180c`. The 1,500-fragment Z/color regression also
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passes with zero errors.
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The regenerated authentic two-draw fixture `zsrt139l3f` contains
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`ff000000000a0000` in draw 195973's FRAME header. Its registered-gradient
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simulation passes 22 epochs and 131,072 fragments with zero drops, overflows,
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AXI errors, Z mismatches, or color mismatches. Most importantly, the native
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256x256 output is byte-identical in all 65,536 words to the static corrected
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target: 44,675 black/alpha-zero texels and 20,861 lit/alpha-128 texels.
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## Accepted fit
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The owner-controlled Quartus 26.1 GUI compile completed successfully on
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2026-07-19. The accepted RBF is 4,112,384 bytes with SHA-256
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`55b23b94f51f1aab271d91aa4fa766561c044b9633146f25f4242b431f6ce902`.
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All signoff classes are nonnegative:
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- EMIF setup WNS `+0.083 ns`, TNS `0.000 ns`;
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- 25 MHz design setup WNS `+6.324 ns`, TNS `0.000 ns`;
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- hold minimum `0.000 ns`, with zero TNS;
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- recovery minimum `+1.074 ns`;
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- removal minimum `+0.017 ns`;
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- minimum-pulse-width minimum `+0.200 ns`.
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Final resources are 38,387 / 46,800 ALMs (82%), 5,327,792 / 7,331,840
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block-memory bits (73%), 344 / 358 RAM blocks (96%), and 160 / 376 DSP
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blocks (43%).
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## Hardware acceptance
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The RBF checksum was verified on the DE25-Nano and `core_loader.sh` loaded it
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successfully; `fpga0` reported `operating`. The authentic 22-epoch
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`zsrt139l3f` fixture then passed every texture CRC, staging, fresh-drain, and
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zero-drop gate. Its 307,200-word framebuffer has SHA-256
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`e2b9f847fb64f5dbc70f112df91c6fccc54bf439138f772927150ff99aa026ce`,
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byte-identical to production simulation. The native target contains exactly
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20,861 lit/alpha-128 pixels and 44,675 black/alpha-zero pixels in its 256x256
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region, proving that draw 195973 preserves the destination alpha byte on
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silicon.
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The complete 311-epoch f52 scene was then replayed on the same RBF. All
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epochs completed with zero fragment drops and its framebuffer remained
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byte-identical to simulation at SHA-256
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`d0047677371a0f6e4e319458926f604a8599c92baaf34d09b8e1fd452e31662b`.
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HDMI therefore ends on the readable f52 scene. The accepted artifact is now
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the board's standard `/home/terasic/cores/retroDE_ps2.core.rbf`; the previous
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artifact is retained as `retroDE_ps2.pre_ch435.core.rbf`.
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