The per-triangle gradient engine already time-shared ONE divider across all
GRAD_STEPS attributes, but computed every grad_load_num[0:GRAD_STEPS-1] numerator
IN PARALLEL — ~44 wide multiplies (~100 physical DSP) for once-per-triangle setup
consumed one-at-a-time. Pure redundant hardware; the design was DSP-maxed
(187/188, 99%) so nothing new could fit (fog needed 191/188).
Replace the parallel bank + the grad_num_q[] pre-latch array with grad_num_step:
computes ONLY the current grad_step's numerator from ONE mux-selected pair of
signed multipliers (attribute triple by grad_step>>1, axis by grad_step[0]; shared
da1/da2, two shared products, signed subtract, <<<20). grad_word_q/grad_slot are
held stable the whole solve, so it is bit-identical to the old grad_num_q[grad_step].
Removed grad_num_dadx/dady (inlined once). FSM sequencing and throughput unchanged.
Width note: da1/da2 are 33-bit (products 50-bit), NOT operand-width 32-bit — the
original (a1-a0) lived in a signed-64-bit expression context and never wrapped;
full-32-bit Z with |a1-a0|>2^31 needs the wider intermediate. tb_gs_grad_num_equiv
(extreme signed corners + 200k random = 494770 checks, 0 errors) caught a 32-bit
first cut that f52's real data never exercised.
Resource (26.1 Seed-3 fit): DSP needed 168->83 / final placement 187->119, i.e.
99% -> 44%, ~85 blocks reclaimed (Codex gate >=70 met). ALM 40458->38784 (86->83%).
RAM 322/358 unchanged. Timing CLEAN: setup +0.077, all classes >=0, 0 violated.
Verification: tb_gs_grad_num_equiv 0/494770; f52 replay BYTE-IDENTICAL golden
d0047677 (drops=0, occupancy unchanged); gradient/perspective/texture regressions
(tri_interp, grad_divider, persp_uv, zbuffer, fog_persp, textured_triangle,
triangle/perspective/combined/gouraud demos) all PASS. Byte-identical => the
screen is unchanged; this is the resource unlock for fog + coverage.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
The fog blend's tex_color*F multiply landed on the texture->color critical path
(u_texcache RAM -> u_tex|tex_color -> mult_126 -> raster_pixel_color_q, 46ns,
-6.165ns setup). Fog is a proven no-op for the current board scene (96.5% F=255),
so pay zero for it here.
FOG_ENABLE (default 1, byte-identical fog) added to gs_stub; each fog mux gated
(FOG_ENABLE && ras_fge) so FOG_ENABLE=0 constant-folds the entire fog cone away
(multiply, FOGCOL adders, s2_fog_f/persp_fog_f5 interp). Threaded through
top_psmct32_raster_demo_bram; set FOG_ENABLE(1'b0) on the active GS_SH3_LPDDR_FB
board arm (elsif at :1086, the one the QSF profile compiles). Fog stays default-on
everywhere else.
Verified: FOG_ENABLE=1 fog TBs unchanged PASS; FOG_ENABLE=0 (new tb_gs_fog_disabled
+ board scene TB) emits raw color = pre-fog datapath; board elaborates clean.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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>
RTL (GS rasterizer, EE core stub, platform bridge, LPDDR4B path), sim regression
(272 TBs), docs, and tooling. Copyrighted PS2 content (BIOS, game code, GS dumps,
and all dump-derived textures/traces) is excluded via .gitignore and stays local.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
thejayman77