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Work-In-Progress: First revision Gerbers not yet manufactured or tested. These notes need updating.
Designed for use with the Alveo U25 in systems that do not support PCIe Bifurcation. The Alveo U25 has an x16 PCIe interface that is bifurcated to two x8 interfaces, one for the SFC9250 X2 GbE Controller and the other for the XCZU19EG FPGA.
Check out the simpler PCIe_x16-to-x8_Debifurcator if you only need to connect to the FPGA.
A straddle-mount PCIe x16 Connector is required, such as: 10025026-10103TLF, 10025026-10003TLF/10146027-A40010LF and two SlimSAS Connectors such as U10A474240T.
Related Projects: alveo_u25_notes, AlveoU25_JTAG_Adapter, ATX_Boot_Delay, PCIe_x16-to-x8_Debifurcator
TODO
The Alveo U25's XCZU19EG uses its ARM processor to configure the FPGA's Programmable Logic (PL) bitstream. It is difficult to get this to finish within the PCIe Specification's 100ms time limit. Motherboard boot must be delayed to allow the FPGA to configure itself before PCIe devices are enumerated by the host system. This can be accomplished by toggling the POWER button, then pressing and holding the RESET button for a second before releasing it. Or, :
All differential pairs are length-matched to within 1mm both inter-pair and intra-pair.
The PCIe Connector's Mounting Post needs to be snapped off with needle-nose pliers.
4-Layer PCB stackup taken from JLCPCB.
Differential Impedance parameters were calculated using the DigiKey Online Calculator.
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