Waveshare Builds a Raspberry Pi 5 "Tower of Power" with a Four-Port PCI Express Expansion HAT
Add-on lets you connect up to four PCIe-based devices to a single Raspberry Pi 5 — but beware the shared bandwidth.
Embedded and hobbyist electronics specialist Waveshare has launched an add-on for those who can't quite decide what to use the Raspberry Pi 5's PCI Express lane for — by expanding it to support up to four devices at once.
"[The] Four-Ch[annel] PCIe FFC [Flat Flexible Circuit] Adapter Board for Raspberry Pi 5 expands the PCIe interface of the [Raspberry] Pi 5 to four […] FFC connectors [and] supports stacking multiple PCIe HATs," Waveshare writes of its latest Raspberry Pi add-on. "PCIe Gen. 2 transmission speed: the theoretical transmission speed of the Gen. 2 mode is up to 5Gb/s; the measured reading/writing speed is approx 500MB/s."
The Raspberry Pi 5 launched back in October 2023, and came with a big surprise: a user-accessible PCI Express Gen. 2 lane, which could be run out-of-spec as a Gen. 3 lane in some instances, presented on a 16-pin flat flexible circuit (FFC) connector to the board's left-hand edge. The official Raspberry Pi M.2 HAT+ turns that into an M.2 interface, well-suited to Non-Volatile Memory Express (NVMe) storage and accelerators for machine learning and artificial intelligence (ML and AI) workloads — but what if you can't decide which of the two you want? Enter Waveshare's latest add-on.
The Waveshare board, brought to our attention by CNX Software, sits on top of a Raspberry Pi 5 and splits that PCIe lane into four FFC connectors through an on-board passively-cooled ASMedia ASM1184e switch. Each of these connectors provides its own PCIe Gen. 2 lane — meaning it's possible to create a "tower of power" with a total of four PCIe-based HAT boards plus the expansion HAT itself.
There are a couple of caveats, however. The biggest is that every device connected through the HAT still communicates with the Raspberry Pi 5 through a single PCI Express Gen. 2 lane — meaning bandwidth is shared, so if you're trying to access four full-speed devices at the same time each will run at roughly one-quarter the throughput. It's also not possible to run the board at PCIe Gen. 3 speeds, which will impact the performance of NVMe drives and AI accelerators.
The Four-Channel PCIe FFC Adapter Board is available on the Waveshare store, priced at $21.99 before volume discounts.