The release of the Raspberry Pi 4 brought us a new SoC, up to 4 GB of memory, and, most importantly, we said goodbye to this jerky USB-to-USB and Ethernet solution. The Raspberry Pi 4 has a PCI Express interface, which is hidden under some chips. If you can solder very well, you can add a PCIe x1 device to the new best single-board computer.[Thomasz] Take a look at the Raspberry Pi 4 and connect the new USB 3.0 chip to the PCI Express interface of the SoC. That means if you remove this chip and have some very fine wires, you can plug in a real PCI Express slot. The removal of the chip is quite easy with a hot air gun, although a few caps are confused. If you put that in an ultrasonic cleaner, you have a blank canvas to practice PCI magic.
Six wires or three differential pairs are required for this hack. There is a reference clock, a transmission on track 0 and a reception on track zero. Starting from a PCI Express riser [Thomasz]these connections were detected and some wires were soldered. On the Pi side, some capacitors had to conform to the PCI Express specification, but soldering is not bad. With a small tip on an iron and a microscope you can achieve a lot.
The Pi has been successfully connected to a PCI Express riser card, along with the ground, 5V, link reactivation, and a power signal. All you have to do is plug in and test a PCI card. This was not as good as expected because the PCI Express adapter was not popular with the Raspberry Pi kernel. In subsequent experiments, an Adaptec SAS controller worked. Does this mean external graphics card for the Pi? No not really; This is just a trace of PCIe where modern graphics cards need an x1