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>
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>
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>
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