mfolejewski/pcie_mux

This repository documents a hardware circuit design: a one to two analog multiplexer that lets a single PCIe lane be switched between two different endpoints while keeping the signal clean enough to run at PCIe Generation 2 or Generation 3 speeds. It is meant for engineers building embedded systems or carrier boards, not for anyone looking for software to install. The high speed differential signals, meaning the transmit, receive, and reference clock lines, are switched using a Texas Instruments chip built for exactly this purpose and rated for data rates well above what PCIe Gen3 needs. Supporting control signals like reset, wake, and clock request are handled separately by smaller analog switch chips. The design was built for a real product called MirkoPC, where it automatically decides which device gets the PCIe connection: if a solid state drive is plugged into the M.2 slot, the system routes PCIe to it, and if that slot is empty, it falls back to an external connector instead, with two LEDs showing which path is currently active. The included PCB layout follows careful high speed design practices, including controlled spacing between paired signal traces, tight matching between the two wires in each pair, and extra grounding vias placed wherever the signal moves between layers. The design files are provided in Altium Designer's format, though the repository notes that KiCad users can import Altium projects directly through KiCad's own importer. Documentation includes schematics as PDF and image files, high resolution photos of the finished board, and pictures from the real MirkoPC product it was built for. The repository is explicit that this is provided for educational and reference use, with no warranty, and that anyone using the design is responsible for verifying it themselves before manufacturing. It is licensed under the CERN Open Hardware Licence, Strongly Reciprocal variant, which requires that any distributed modifications stay open under the same license.