C4 is an SRCC pin (IS_CLK_CAPABLE=1, IS_MASTER=0 in the Vivado device
model), not an MRCC as earlier comments claimed. SRCC cannot drive BUFG
through dedicated routing, so the previous CLOCK_DEDICATED_ROUTE=FALSE
override forced fabric routing and burned ~5 ns on the ft_clkout path
(WNS -5.362 ns in the d36a4c9 build).
Swap to BUFIO + BUFR for USB_MODE=1 (50T/FT2232H): SRCC → BUFIO → BUFR
is the standard 7-series path for regional clock distribution. All
ft_clkout-domain logic (FT2232H FSM, toggle CDCs, USB FIFO flops) is
contained in bank 35 / one clock region, so regional distribution is
sufficient. USB_MODE=0 (200T/FT601) keeps the BUFG because D17 is a
proper MRCC pin.
Removed CLOCK_DEDICATED_ROUTE=FALSE from both the XDC and the build
script — no longer needed with dedicated BUFIO/BUFR routing.
- Add set_false_path -hold for source-synchronous ADC IDDR paths in
adc_clk_mmcm.xdc (eliminates 8 hold violations from build 12)
- Add DDR falling-edge input delay constraints to xc7a50t_ftg256.xdc
(parity with 200T XDC)
- Reorganize scripts/ into target subdirectories: 50t/, 200t/, te0712/,
te0713/, utils/ so users can run the correct build for their hardware
- Delete obsolete build scripts (build17-20) superseded by build_50t/200t
- Update project_root paths in all moved scripts (.. -> ../..)