Found while helping verify the user's own schematic: clk_sys (the PLL-
generated 64MHz system clock) was purely internal to
fpga_neural_v2_top.v -- never reached a physical output pin. The real
external SDRAM chip cannot function without its own CLK input driven
from the board; this was missing from every prior P&R run this
session, none of which ever routed a real clock to the SDRAM interface.
Added `sdram_clk` output port (driven directly by clk_sys), assigned
to J4 (bank 6, GR_PCLK6_0 -- a real clock-capable ball, confirmed free
via Trellis iodb.json). Verified via real synthesis (0 errors) and
nextpnr-ecp5 place&route: the pad-forwarded clock merges with the
existing internal clock net (as expected, both are the same clk_sys
signal), achieving 66.61 MHz post-route -- PASS at the 64 MHz target
(the pre-route estimate of 49.73 MHz was a placement-only pessimistic
number, superseded by the real post-route result). Smoke test
re-verified (tb_fpga_neural_v2_top_smoke.v, 11/11 PASS).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013xXuuRUWZScuo1DeYJxs3v
micheleandClaude Sonnet 5
b4f33388a9