michele/FPGA-Neural
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

test: fix tb_sdram_arbiter_n.v hang, root-caused as testbench bug (EXP-0069)

Browse Source 
TEST2 fired all 3 simulated requesters' one-shot req pulse
unconditionally, not waiting for each one's own grant -- an
unrealistic stimulus that doesn't match packed_slot.v's real
S_MEMWAIT usage (wait for grant, then fire). Rewrote with parallel
fork branches, each waiting for its own req_grant first, still
exercising the real simultaneous-activation contention case.

7/7 PASS, 0 errors. sdram_arbiter_n.v is now genuinely verified, not
just written.

Full writeup in hardware/v2/logs/experiments.log EXP-0069.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MUG92aM9m68TRc4rG55BcC
This commit is contained in:
michele
2026-09-17 08:44:46 +02:00
co-authored by Claude Sonnet 5
parent e25e4a1506
commit afff0c4f02
2 changed files with 65 additions and 17 deletions
Download Patch File Download Diff File Expand all files Collapse all files
hardware/v2/logs/experiments.log
+33
View File
@@ -4261,3 +4261,36 @@ that is resolved); (3) swap mig_native_adapter.v into packed_slot.v's
memory path, replacing the SDR SDRAM placeholder, and re-verify the
N=2 system against real DDR3; (4) real (not out-of-context) P&R with
the actual generated MIG XDC constraints for genuine timing signoff.
EXP-0069 -- sdram_arbiter_n.v hang root-caused: testbench bug, not
arbiter bug (2026-09-17, same autonomous continuation)
CONTEXT: EXP-0068's own next_action flagged tb_sdram_arbiter_n.v as
hanging, arbiter not yet trusted.
ROOT CAUSE: TEST2 asserted req_req for all 3 simulated requesters on
the SAME cycle as req_active, then dropped req_req one cycle later
UNCONDITIONALLY -- but the arbiter only grants ONE requester (lowest
index) at a time; slots 1 and 2's one-shot req pulse was long gone by
the time their own turn actually arrived, so they never issued a real
ctrl_req and the test's own `while (!req_ready[1])` waited forever.
This is a testbench-stimulus bug, not an arbiter bug: it modeled an
UNREALISTIC requester (fire-and-forget regardless of grant status)
that does not match how packed_slot.v's own real S_MEMWAIT state
behaves (wait for mem_grant, THEN fire the one-shot pulse) -- the
exact pattern EXP-0066 already established as required and correct.
FIX: rewrote TEST2 with 3 parallel fork branches, each waiting for its
OWN req_grant before pulsing its OWN req_req -- matching packed_slot.v's
real usage exactly, still exercising the real simultaneous-activation
contention case (all 3 raise `active` on the same cycle).
RESULT: 7/7 tests, 0 errors. sdram_arbiter_n.v is now genuinely
verified, including the real simultaneous-multi-requester contention
case with one-shot-pulse requesters (the EXP-0066 risk class).
DECISION: sdram_arbiter_n.v is trusted for integration.
next_action: same as EXP-0068's (3)/(4) -- swap mig_native_adapter.v
into packed_slot.v, re-verify N=2 against real DDR3, then real P&R
with the generated MIG XDC.