We’re big fans of the Raspberry Pi Compute Module 4 (CM4). The inclusion of a PCIe slot opened up a world of possibilities (which Jeff Geerling is exploring) but what if you want say, four PCIe slots? Happily, Waveshare has decided to do something about this as it releases the PCIe-Packet-Switch-4P, brought to our attention by CNX-Software, that uses an ASMedia ASM1184e PCIe switch to connect four devices to the CM4’s single-lane PCIe Gen 2 interface.
Admittedly, that’s not going to get you to typical GPU speeds, and may be further limited, as the Chinese-language wiki that accompanies the board states the bandwidth is 500Mbps, which seems to be missing a zero and may be a mistake.
The IO carrier board measures just 3.2in x 1.5 inches (82 x 39mm) and needs a 12v power supply. This can come via the PCIe bus, or through a DC jack. If no 12v can be found, a 5v supply can be substituted, but the board comes with warnings that this will flow back to the 12v rail, and precautions need to be taken to ensure the correct functioning of the board under these conditions. The documentation has no elaboration on how to do this but we can see what looks like a "floppy drive" power connector which supports 12v and 5v on the underside of the board.
The PCIe-Packet-Switch-4P is an add-on board that connects to a Compute Module 4 IO carrier board that already has a single Mini PCIe slot exposed. The board slots into the Mini PCIe slot, held in place with brass standoffs. It is also compatible with other Mini PCIe enabled carrier boards such as that on Waveguide’s own CM4 carrier board, which adds HDMI, Ethernet, USB ports, GPIO and three ribbon cable connectors.
Cards that work with Raspberry Pi over PCIe include USB 3 controllers, SSDs, SATA interfaces, Ethernet controllers, and even Creative’s Sound Blaster X-Fi Xtreme sound card. Pi tinkerer and friend of the Tom’s Hardware Pi Cast, Jeff Geerling, keeps a list of cards he’s tested at his site.
The Waveshare PCIe-Packet-Switch-4P currently sells in China for around $23. It isn’t currently available on the Waveshare English Store, but we’re hopeful it will make it to eager Raspberry Pi fans across the world.