thejayman77
2e2c1e9ca6
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>
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/.