thejayman77
064484c50d
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>
retroDE_ps2 Planning Docs
This directory is the working design scaffold for the PS2 core.
Purpose:
- define the intended repository shape before RTL lands,
- define subsystem boundaries before implementation choices harden,
- document what each block owns, what crosses the boundary, and how we will validate it.
Recommended reading order:
- repo_layout.md
- phase0_checklist.md
- contracts/README.md
- stub_module_plan.md
- wave2_dma_gif_plan.md
- wave25_memory_backed_dma_plan.md
- wave26_multi_beat_dma_plan.md
Relationship to references/:
references/is the research library.docs/is the project-definition layer.
Rule of thumb:
- If a file explains PS2 hardware as it exists, it belongs under
references/. - If a file explains how
retroDE_ps2intends to model, partition, or validate that hardware, it belongs underdocs/.