Ever since people figured out that the Raspberry Pi 4 has a PCIe bus, the race was on to be the first to connect a regular PCIe expansion card to a Raspberry Pi 4 SBC. Now [Zak Kemble] has created a new approach, using a bridge PCB that replaces the VL805 USB 3 controller IC. This was also how the original modification by [Tomasz Mloduchowski] worked, only now it comes in a handy (OSHPark) PCB format.
After removing the VL805 QFN package and soldering in the bridge PCB, [Zak] confirmed that everything was hooked up properly and attempted to use the Raspberry Pi 4 with a PCIe extender. This showed that the Raspberry Pi would happily talk with a VL805-based USB 3.0 PCIe expansion card, as well as a Realtek RTL8111-based Ethernet card, but not a number of other PCIe cards. Exactly why this is is still unclear at this point.
As a bonus, [Zak] also found that despite the removal of the VL805 IC from the Raspberry Pi rendering its USB 3 ports useless, one can still use the USB-C ‘power input’ on the SBC as a host controller. This way one can have both PCIe x1 and USB on a Raspberry Pi 4.
This is the third iteration we’ve seen for using PCIe with the Pi. If you’re building on the work of [Thomasz Mloduchowski], which inspired [Colin Riley] to add expanders, and now this excellent hack by [Zak], we want to hear about it!