Roflin
530d58df4f
A/B on identical seeds rather than comparing against a different sweep, since
seed-to-seed spread on this design is larger than the effect being measured:
seed 1 clk seed 2 clk SB_DFFE SB_LUT4
before 28.72 27.04 934 2818
after 29.07 26.39 1038 2959
So +104 FFs, +141 LUTs, and about -2.4% fmax on the worst seed while seed 1
improved -- most of the spread is placement noise over a modest real cost.
8/8 seeds still close; best seed 3 at 29.74 MHz is 1.24x over the 24 MHz
target.
Also records why the storage covers the full low nibble rather than only the
registers libogc2 touches: a sparse decode would silently drop writes to
anything unlisted, which is exactly the behaviour this replaced. Noted as the
obvious thing to narrow if clk margin ever needs reclaiming.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>