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>
rtl/platform
retroDE-specific platform integration. Matches docs/contracts/platform.md.
Wave 1 contents
platform_video_stub.sv— free-running raster generator. Default VGA 640x480 timing (overridable per-testbench to tiny values for fast sim). Takesbg_{r,g,b}fromgs_stuband flood-fills the active region. Emits oneEV_MODEper completed frame so testbenches can count frames without sampling raw video.
Scope boundary
This directory owns:
- clock/reset sequencing entry points,
- retroDE-facing video and audio adaptation,
- HPS bridge plumbing (future),
- top-level wrappers not belonging inside PS2 subsystems.
It does not own GS/PCRTC semantics (that's rtl/gif_gs/), SPU2 audio
synthesis (rtl/spu2/), or any PS2 register behavior.
Replacement path
platform_video_stub stays as the platform adaptation layer. What changes
is the upstream pixel source: Wave 1 → flat BGCOLOR from gs_stub,
later waves → fuller GS/PCRTC output including framebuffer scan-out.