Raspberry Pi Compute Module 4 Gains Four PCIe Slots via Carrier Board

Waveshare PCIe-Packet-Switch-4P
(Image credit: Waveshare)

We’re big fans of the Raspberry Pi Compute Module 4 (opens in new tab) (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 (opens in new tab), brought to our attention by CNX-Software (opens in new tab), that uses an ASMedia ASM1184e PCIe switch to connect four devices to the CM4’s single-lane PCIe Gen 2 interface.

Waveshare PCIe-Packet-Switch-4P

(Image credit: Waveshare)

Admittedly, that’s not going to get you to typical GPU speeds, and may be further limited, as the Chinese-language wiki (opens in new tab) 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 (opens in new tab), 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 (opens in new tab), Jeff Geerling, keeps a list of cards (opens in new tab) 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 (opens in new tab), but we’re hopeful it will make it to eager Raspberry Pi fans across the world.

Ian Evenden
Freelance News Writer

Ian Evenden is a UK-based news writer for Tom’s Hardware US. He’ll write about anything, but stories about Raspberry Pi and DIY robots seem to find their way to him.

  • TomAVandy
    Nice if one could actually find CM4s anywhere.
  • kharar
    The 500 Mbps limit is real. The chip used is an ASM1184 that only supports PCI express base SPEC 2.0