thejayman77/retroDE_ps2
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Ch443f: coherent Gray readiness CDC + qualified scanout underflow detector

Browse Source 
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>
This commit is contained in:
thejayman77
2026-07-23 23:17:41 -04:00
parent 2e2c1e9ca6
commit 064484c50d
11 changed files with 418 additions and 63 deletions
Download Patch File Download Diff File Expand all files Collapse all files
sim/Makefile
+10
View File
@@ -1299,6 +1299,15 @@ tb_gs_scanout_diag: dirs
@echo "=== run tb_gs_scanout_diag ==="
@cd $(TRACE_DIR) && $(VVP) $(BUILD_DIR)/tb_gs_scanout_diag.vvp
tb_gs_scanout_cdc_qual: dirs
@echo "=== build tb_gs_scanout_cdc_qual ==="
$(IVERILOG) $(IVERILOG_FLGS) \
-o $(BUILD_DIR)/tb_gs_scanout_cdc_qual.vvp \
-s tb_gs_scanout_cdc_qual \
$(RTL_SRCS) $(TB_ROOT)/gif_gs/tb_gs_scanout_cdc_qual.sv
@echo "=== run tb_gs_scanout_cdc_qual ==="
@cd $(TRACE_DIR) && $(VVP) $(BUILD_DIR)/tb_gs_scanout_cdc_qual.vvp
tb_gs_scanout_restart: dirs
@echo "=== build tb_gs_scanout_restart ==="
$(IVERILOG) $(IVERILOG_FLGS) \
@@ -6321,6 +6330,7 @@ run: tb_top_psmct32_sh3_zs640b24_cap tb_top_psmct32_sh3_zint640b24
.PHONY: tb_top_psmct32_sh3_zs640c24c_cap tb_top_psmct32_sh3_zint640c24c sh3_zs640c24c_fixture sh3_zs640motionabc_bootlet
run: tb_top_psmct32_sh3_zs640c24c_cap tb_top_psmct32_sh3_zint640c24c tb_gs_axi_w_regbuf tb_gs_axi_aw_regbuf tb_gs_axi_r_regbuf
run: tb_gs_lpddr_scanout_lb tb_gs_scanout_binomial_lookahead tb_gs_scanout_diag tb_gs_scanout_restart tb_gs_scanout_cdc_qual
run: tb_ee_fetch tb_gs tb_intc tb_platform_video tb_bgcolor_via_dma tb_sif_mailbox \
tb_sif_command_echo tb_sif_command_echo_rearm tb_sif_negative_path \