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 Seed-3 fit of the Ch443f scanout hardening exposed one setup family in the
EMIF (iopll_0_outclk0, 3.225 ns) domain: u_zc_emit|u_z|cache_dirty -> awaddr[*],
WNS -0.062 / TNS -0.203, skew-dominated (-0.064 clock skew; the 5-level logic
path itself would land ~+0.002 at zero skew). Not the Ch443f logic — the added
EMIF-domain logic nudged this marginal Ch357-era control path negative.
Fix (Codex-directed, minimal): the normal-eviction AW address is a pure function
of the cache line's beat, known when the line is installed. Preload it in S_FILL_C
alongside cache_beat<=pf_beat (awaddr <= ZBASE + (pf_beat<<5)), and drop the two
later awaddr assignments gated by cache_dirty (the scene_flush branch and the
dirty cache-miss branch) — those now only assert awvalid on the already-prepared
address. Clear-path awaddr assignments unchanged. No new FSM state, pipeline
stage, buffer, or protocol change.
Safe: a freshly filled line cannot be dirty before S_FILL_C installs it; the
address is stable across hits and scene flushes; after a dirty eviction the next
fill re-runs S_FILL_C; clear invalidates the cache so the first subsequent fill
overwrites the clear address before any normal eviction. This removes the control
cone rather than placing around it, so closure is seed-robust.
Regressions green: z_rmw/zc_emit/axi_master_elastic/zbuffer/z_flush_writer/
tile_zflush, full Ch443f scanout set, sh3_zint (Z 0/53760, COLOR 0/11092),
sh3_zrop (errors=0), and f52 byte-identity (Z 0/307200, COLOR 0/245760, drops=0).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Harden the LPDDR scanout underflow diagnostic (Codex direction). Keeps the
Ch443e 4-buffer + lead-2 fix; adds no 5th buffer.
RTL (gs_lpddr_scanout_lb):
- Replace the raw-binary next_fetch readiness sync with a reset-aware GRAY
code. next_fetch is monotonic between frames, so one Gray bit changes per
increment; the 2-FF-synced + decoded nf_v is always a real prior frontier
(monotone, burst-safe), never a torn multi-bit combination. (A plain
toggle-per-change handshake dropped bursts when two increments landed in one
sync window; that is why the earlier attempt under-read nf_v and false-tripped.)
fs_edge_v overrides the lone multi-bit reset transient.
- Qualify the underflow: only a miss persisting >= QUAL_CYCLES (4) sets sticky
underflow. uf_pmax_q records the longest streak and uf_qual_q whether any
qualified, so a host can distinguish a 1-cycle CDC lag from a real late row.
- Atomic snapshot: scan_y/nf_v/pmax/causes/vphase/line_valid all latched the
same video cycle on the first qualified miss.
ABI: 0x120 adds [15:12]=live pmax (2-FF synced via scan_diag_pmax_i). 0x124
[29:20] now carries pmax-at-capture (was nf_s0). Bridge dst reg kept 10-bit.
SDC: scanout diag bundle source count 37 -> 31 (nf_s0[10] -> pmax[4]); new
async-in cut + max_skew/net_delay for the next_fetch Gray CDC; stage-0 cut for
the live pmax sync.
Tests: new tb_gs_scanout_cdc_qual (async-clock focused: no false event from the
readiness transition or ordinary sync latency; sub-QUAL transient does not
qualify; genuine late row qualifies with a self-consistent atomic snapshot;
frame reset + mod-4 reuse re-arm the detector). tb_gs_scanout_diag updated for
the pmax field. Tie off scan_diag_pmax_i (+ pre-existing clut_* gap from the
fog baseline) in the four .* bridge/integration TBs.
Regressions green: scanout (cdc_qual, binomial_lookahead, diag, restart,
lpddr_scanout_lb x3), regbuf (r/aw/w), bridge + 3 pad integration TBs, and the
f52 top-level golden FB (Z 0/307200, COLOR 0/245760 mismatch, drops=0).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
The Ch443d board per-frame diagnostic identified the real displayed-frame
failure as a BINOMIAL vertical-lookahead starvation: displaying source
row r while interpolating r-1/r/r+1, the prefetch led by only one row
(next_fetch <= disp_row+1), so the lookahead row r+1 was still in flight
when the 3x3 filter read it (board: scan_y=33, nf_v=34, cause_lookahead=1,
read-error=0, deterministic every frame).
Fix (BINOMIAL_3X3_FILTER only; legacy 2/3-buffer, lead-1 paths unchanged):
- Add a 4th rotating line buffer (lb3) with its own RAM-local write/read/
cache registers. The 3x3 filter needs r-1/r/r+1 resident (3 buffers), so
leading by 2 (fetch r+2 while displaying r) without overwriting r-1
requires a 4th buffer.
- Prefetch lead-2 for binomial: disp_row_limit_e = disp_row+2. The in-flight
r+2 lands in the 4th buffer (b+2 mod 4), always distinct from prev/cur/next
(b-1/b/b+1 mod 4), so it never clobbers a row being read.
- Modulo-4 rotation everywhere: V_SOURCE_BUF%4, stretch_buf_q, next_fetch_buf,
reset alignment at V_SOURCE_START, and the read-cache prev/cur/next case
extended to 4 branches with (b-1)/b/(b+1) mod 4 selection + first/last-row
clamps preserved.
New tb_gs_scanout_binomial_lookahead reproduces the board condition under
realistic EMIF latency (LAT=7) + backpressure and proves: NO binomial
lookahead underflow, correct 3x3 output across modulo-4 wrap + clamps (full
oracle, 1280 px), and coverage that mid-frame rows past V_SOURCE_START+1
with vphase!=0 were exercised under prefetch pressure.
All green: binomial (4-buffer, identical output), lookahead (new),
scanout_lb {,_hstretch,_psm32_256,_fb}, scanout_restart, scanout_diag,
ps2_hps_bridge, and the complete f52 replay BYTE-IDENTICAL (Z 0/307200,
COLOR 0/245760). Also commits the Ch443d board evidence that identified
this defect. No Quartus/board/push from here.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Closes the last currently-visible EMIF-handshake -> FSM setup family the
Ch443c fit exposed (-0.043/-0.022/-0.005 ns), the read-response analogue
of the AW/W buffers.
- gs_axi_r_regbuf: one-entry FULLY-registered AXI R buffer (the R twin of
gs_axi_w_regbuf). Buffers the complete {rdata,rresp,rlast}; u_rready =
!full only (NO combinational dependence on the texture FSM's d_rready);
captures on u_rvalid && u_rready; d_rvalid = full with the payload held
stable until d_rvalid && d_rready; resets only . Inserted between
read-arbiter s2 and gs_texture_cache (u_texf_rbuf). The arbiter is
unchanged -- it completes its R transaction into the buffer, which then
owns delivery to the fill FSM. Cuts EMIF rvalid/rdata -> fst.F_R.
- gs_texture_cache: drop the unobservable fill_data_q reset. F_DRAIN (its
only reader) is reachable only after F_R loads it, so the reset value is
never observed; removing it kills the separate lock_sync|dreg[1] ->
fill_data_q[80] setup path (-0.005 ns).
- New tb_gs_axi_r_regbuf: exactly-once/in-order, randomized responses +
stalls, full backpressure, the full && d_rready no-fall-through case,
{rdata,rresp,rlast} stability, reset-while-empty AND reset-while-full.
All green: r-buffer TB, texture_cache, texture_psmt8_clut, scanout_lb,
scanout_restart, scanout_diag, ps2_hps_bridge, rd_arb, and the complete
f52 replay BYTE-IDENTICAL (Z 0/307200, COLOR 0/245760). No Quartus/board/
push from here.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
The Ch443 board A+B diagnostic captured a WARM-UP miss, not a displayed-
frame miss: the line-buffer reader is enabled by video_src_emif
immediately, but the HDMI mux only switches to it at the next vsync, and
the diagnostic (cleared only on !enable) froze that pre-display capture.
scan_y=32/nf=32 was the expected pre-display warm-up, and line_valid is
sticky so it only meant SOME row had loaded, not that row 32 was valid.
Two fixes (all accepted Ch443 timing repairs kept: AW buffer, F_SETTLE +
drain multicycle, tile max-skew, monolithic tex_mem):
1. Per-frame diagnostic: clear diag_valid_q on fs_edge_v as well as
!enable (mirrors underflow_v). Discards the warm-up capture and
records the first miss, if any, AFTER the real frame boundary.
2. Frame-restart latency: in L_R, after the single-beat response is
accepted, if fs_pending || fs_edge_e, abandon the remainder of the
obsolete row -- no beat commit, no next old-row AR, no publish/
increment -- and return to L_IDLE, which restarts at V_SOURCE_START.
Protocol-safe (the accepted AXI transaction is complete); removes up
to a full row of restart latency during vertical blanking, so the
restarted prefetch leads the first displayed row.
New tb_gs_scanout_restart proves: mid-fetch frame-start accepts the
in-flight response, issues NO further old-row AR, restarts at row 32,
loads rows 32/33 before active consumption, and no post-restart
underflow. Regressions green: scanout_lb {,_binomial,_hstretch,
_psm32_256,_fb}, scanout_diag (per-frame), ps2_hps_bridge, and the
complete f52 replay BYTE-IDENTICAL (Z 0/307200, COLOR 0/245760).
Also commits the previously-untracked Ch443 board A+B evidence
(docs/hardware/ch443_board_validation/: verdict, 3-session raw, board
FB, RBF sha). No Quartus/board/push from here.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
The four-bank tex_mem split (27dfd0b) closed the -0.370 EMIF drain
write-address fanout but the owner GUI fit showed the fitter SCATTERED
the banks, pushing the DESIGN-clock sampler read cone
(ras_v0_x -> perspective-UV -> texel addr -> tex_mem portbaddr, the
design's fundamental ~40ns critical path) to -2.208 ns. Net worse.
Codex's call (Option 1 + honest write-side multicycle), implemented:
- Restore the MONOLITHIC 65536x32 tex_mem, recovering the clean 25 MHz
read-cone placement. Sampler/read-address path stays fully timed
(Ch439g); nothing about it is relaxed.
- Make the EMIF drain write genuinely two-cycle: new F_SETTLE state
between F_DRAIN and F_WRITE. drain_idx_q/drain_word_q are loaded in
F_DRAIN, HELD unchanged through F_SETTLE (the load block gates on
F_DRAIN), and the RAM write + CRC happen at the later F_WRITE edge.
- SDC: fail-closed 2-cycle-setup / 1-cycle-hold multicycle from ONLY
u_texcache|drain_idx_q[*] to tex_mem (a 6.45 ns EMIF window for the
drain write-address). Scoped -from the drain regs, so the sampler
read path (different launch regs) is untouched. HALTs if tex_mem is
present but drain_idx_q renamed.
The AW buffer (gs_axi_aw_regbuf) and the tile-CDC max-skew 2.5 relax
from 27dfd0b are KEPT unchanged (both closed their families in the fit).
Verified: tb_gs_texture_cache (monolithic + F_SETTLE, distinct-per-byte-
lane + full-word, 0 errors), aw/w regbuf, texture_psmt8_clut,
scanout_diag, ps2_hps_bridge, and the complete f52 replay BYTE-IDENTICAL
(Z 0/307200, COLOR 0/245760). No Quartus/board/push from here.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Ch442's fit exposed two failing setup families (plus a stale max-skew).
Attack both structurally; no reseeding.
Family 1 - AWREADY -> Z-FSM (-0.410): gen_p2c_ff[23] (EMIF AWREADY)
reached u_zc_emit|u_z's S_SFLUSH_AW/S_FILL_R next-state combinationally.
Ch441 registered only the W channel; add the AW twin:
- new gs_axi_aw_regbuf (one-entry fully-registered AW buffer), inserted
in zc_emit between u_z's AW output and the arbiter s2 AW port. The FSM
now sees registered occupancy, never EMIF's combinational AWREADY.
Family 2 - texcache drain_idx_q -> tex_mem (-0.370, x7): a single index
fanned across the whole 65536x32, 128-M20K macro. Split by WIDTH into
four 65536x8 banks, each with its own (* preserve, dont_merge *) write-
address launch register; write the four byte lanes together in F_WRITE;
reconstruct the sample word by concatenating four registered read bytes.
Selector structure and 1-cycle read latency unchanged; total M20Ks
unchanged (4x32 == 128); fill_crc still sums the full 32-bit word.
Max-skew: relax ONLY the Ch357 tile-write CDC set_max_skew 2.0 -> 2.5
(quasi-static bundle, >=2 dclk stability window); retain set_net_delay
2.0 (the real arrival bound). SDC comment updated.
Tests: new tb_gs_axi_aw_regbuf (AW scoreboard: exactly-once/order/no-
combinational-AWREADY-bypass/stable-while-stalled); tb_gs_texture_cache
strengthened to distinct-per-byte-bank data + per-bank + full-word
checks. All pass: aw/w regbuf, texture_cache, texture_psmt8_clut,
scanout_diag, ps2_hps_bridge, and the complete f52 replay BYTE-IDENTICAL
(Z 0/307200, COLOR 0/245760).
No Quartus, board, or push from here. Ready for one owner GUI fit.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Codex review containment/observability fixes (no behavior change, no redesign):
- scanout_lb: add !fs_edge_v to the diagnostic predicate so capture
matches the underflow latch's frame-start CLEAR priority exactly
(no capture on an fs_edge cycle the real latch suppresses).
- bridge: expose a destination snap_valid_q as 0x120[0] — set ON the
payload-capture edge, cleared on synced source-valid deassert — so
valid never leads the bundle by a cycle (was the middle sync stage).
- bridge: forced-synchronizer (SYNCHRONIZER_IDENTIFICATION FORCED) +
dont_merge/preserve on the underflow/read-error/valid chains;
preserve on the bundle capture regs (both domains).
- SDC: stage-0 async cuts on the three sync[0] inputs + the 37-bit
stable bundle hold-false-path + 2ns max_skew + 2ns net_delay, with
fail-closed src==37 / dst!=0 count checks (tile_ram_cdc idiom).
- tb_gs_scanout_diag: +fs_edge-suppression monitor (with coverage that
the coincidence is exercised), +valid-ordering monitor, +snapshot
stability after later misses, +production DUT (V_SOURCE_START=32,
stretch, linear) proving cold-start scan_y=32, +cause/phase packing.
32/32 checks pass.
- doc: production cold start is source row 32 (not 0), base+lookahead
may both assert, and one snapshot narrows but does not prove
starvation vs next_fetch CDC-lag.
Sim set all PASS: focused TB, tb_ps2_hps_bridge, scanout_lb
{binomial,hstretch,psm32_256}, complete f52 replay (FB byte-identical
Z 0/307200, COLOR 0/245760). No Quartus, board, push, or scanout
behavior change.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Read-only diagnostic to disambiguate the three causes folded into
LPDDR_STATUS[5]. bit5 (0x02C) semantics are UNCHANGED.
- gs_lpddr_scanout_lb: register a live (rd_errs!=0) flag in the emif
domain (the raw counter never crosses), and capture the FIRST raw
underflow of each video-source-enabled session as a bundled-data
snapshot (scan_y/nf_v/nf_s0 + base-vs-lookahead cause + line_valid +
vphase), held stable until !enable. The existing sticky underflow_v
latch, fetch FSM, pixel path and arbitration are untouched.
- ps2_hps_bridge: independently 2-FF sync the two split live flags;
latch the snapshot on the rising synced-valid edge (coherent bundled
data). New read-only regs 0x120 SCAN_DIAG_STATUS / 0x124
SCAN_DIAG_FIRST (window addr[37:5]==9); 0x118/0x11C reserved slots
untouched.
- top: drive 5 diag nets per scanout arm like scan_err_w; bit5 assign
unchanged.
- tb_gs_scanout_diag (new): provokes AXI RRESP error, cold-start row-0
starvation, first-failure capture + coherent bridge readback, and
clear-via-video-source-disable (17/17 checks).
- Tie off the new bridge inputs in the four .*-instantiating TBs.
Sim set all PASS: focused TB, tb_ps2_hps_bridge, scanout_lb
{binomial,hstretch,psm32_256}, and the complete f52 replay (FB
byte-identical: Z 0/307200, COLOR 0/245760; sum32=0xaad0b94d).
No fix / gray-code / persistence-filter / scanout checksum. No Quartus,
no board, no push.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Cuts the lone remaining EMIF setup fail (-0.016 ns, -0.259 skew): the combinational
EMIF gen_p2c_ff -> wr_arb s2_wready -> gs_lpddr_z_rmw next-state (st, endpoint
labelled S_FILL_R via the shared encoded state register).
New gs_axi_w_regbuf: fully-registered one-entry W buffer (Option B per Codex).
- u_wready = !full ONLY (registered occupancy) -> EMIF WREADY never reaches the Z
FSM combinationally. NOT a fall-through skid (no !full-OR-d_wready term).
- Buffers WDATA/WSTRB/WLAST; downstream held stable until accepted; exactly-once.
- AW/B untouched; arbiter bready_q unchanged (still arms on real EMIF W handshake).
- z_rmw may enter B-wait once the beat is buffered -- safe: EMIF cannot return B
until the buffered beat reaches it. Single-beat writes -> the 1-beat/2-cycle
buffer rate is far above the Z write rate (no new FIFO pressure).
Wired in zc_emit between u_z W output (zi_*) and the z_w* ports. New file in sim
Makefile RTL_SRCS + synth QSF (both). Focused tb_gs_axi_w_regbuf: exactly-once/order/
payload scoreboard + no-combinational-bypass check (u_wready===!full incl. full &&
d_wready) + downstream-stable check; standalone target + in make run. Texture-cache
+0.016 paths NOT touched. No simulations or Quartus run.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Per Codex review of 471c1af:
1. tb_gs_async_fifo QUAD_WIDTH4 variant now runs at the PRODUCTION 93-bit width
(exercising the odd 23/23/23/24 remainder split) and drives a DISTINCT NONZERO
pattern into every width bank (seq XOR per-bank constants, bank2 inverted), with
the scoreboard checking the FULL reconstructed word. A swapped/broken/zeroed
upper bank now changes the word and trips the scoreboard. Depth-half crossing
(DEPTH=8) + wrap/full coverage retained. mk() is generate-guarded so the 32-bit
variants never elaborate the 93-bit selects.
2. Softened gs_async_fifo comments: 'same total M20K' -> EXPECTED-similar, pending
synthesis (fact -> expectation).
No simulations or Quartus run. Awaiting review before any sim.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Candidate 2 from the accepted structural proposal. Adds a QUAD_WIDTH4_READ
generate branch to gs_async_fifo: like QUADRANT_READ (2 depth x 2 width) but
splits the payload into FOUR width banks, so each preserved read-address launch
register drives ~half the M20K load (targets the 310MHz raddr_hi1_q->mem_hi1
setup family, WNS -0.103). Keeps QUADRANT_READ's proven 2:1 depth OUTPUT selector
unchanged (no new/deeper mux, per the doc's warning). Depth (8192), one-cycle
read latency, ordering, CDC, capacity, and interface are identical.
zc_emit u_req switched QUADRANT_READ->QUAD_WIDTH4_READ. New default-off param
leaves the other two gs_async_fifo instances byte-identical. TB gains a
TEST_QUAD_WIDTH4 variant + standalone Makefile target tb_gs_async_fifo_quad_width4.
NO simulations or Quartus run (per authorization). Awaiting review before any sim.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
My REQ_DEPTH=1024 reduction was wrong: I sized it off a 478 peak from a SMALL
scene. The documented full-f52 replay peak is 6,115 (adjacent frame 3,610; even
2,048 clips) — ch439_timing_convergence_prefit.md. The raster cannot backpressure,
so an undersized FIFO SILENTLY DROPS Z-requests -> corrupt frame. The -0.074 fit
was on an invalid (drop-prone) config. Restore 8,192 as the correctness baseline.
The real timing fix is a registered/skid AR-handshake boundary (arbiter s2_arready
combinational -> texcache F_AR), NOT FIFO shrinking. Packaging that for Codex review.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
The 8K request FIFO was 8x oversized (measured peak ~478; Codex's TB uses 1024).
Its read address routed to 8 spread M20K blocks -> 310MHz EMIF setup miss (-0.103,
MAX_FANOUT can't help: Quartus refuses to duplicate RAM-address regs, Warning 22471).
Shrinking to 1024 (2 blocks): 26.1 fit shows that path GONE, design clk +0.631->+5.693,
RAM 309/358 (86%) -> 277/358 (77%). New worst is a DIFFERENT, skew-dominated EMIF->
texcache-FSM path at -0.074 (TNS -2.032 -> -0.164).
SAFETY GATE before board load: confirm the full zsrt139f52 scene never bursts >1024
Z-requests in flight (peak I have is 478 from a smaller scene). Bump to 2048 if unsure.
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>
Two fixes for the failing STA (Codex-reviewed):
1. gs_texture_unit lerp8: remove the dead 0/255 clamp. For 8-bit taps and f in
0..15, a+floor((b-a)*f/16) is always in [0,255], so the clamp never fired -
but its comparators formed a 161-node combinational loop that failed
design-clock setup by 42 ps (tap[0][11] -> tex_cache_sel_q). Functionally
identical (tb_gs_texture_bilinear + texture TBs bit-identical PASS).
2. SDC: relax the u_zc_emit gray-code CDC max_skew 2.0 -> 2.5 ns. Post-fog
placement pushed actual skew to 2.010 ns (fails 2.0 by ~10 ps). Real ceiling
is the 3.225 ns EMIF period (one gray bit in flight); 2.5 clears the miss and
stays well under it. Documented relax of a conservative round number.
Acceptance (owner fit): no comb-loop warning, no tap->tex_cache_sel_q path,
all setup + max_skew slacks >= 0.
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