compute module

It's been a busy start to the year on my Raspberry Pi PCIe Devices website. Not only have we finally made some significant progress learning about the BCM2711's PCIe bus (both good and bad), I've also added a few dozen new Raspberry Pi CM4-based boards to the site.

In my YouTube video today, I go through four of them in depth, showing how they're built and what they're used for.

The four projects I cover in depth are:

1. Bigtreetech's Raspberry Pad 5
2. Seeed Studio's reTerminal
3. Waveshare's Dual Ethernet 5G/4G base board
4. Ab-log's RPi4-RTC-PoE DIN rail computer

And there are some other projects I'm watching closely as they journey down the road towards production:

Update: The Compute Module 4S is now listed on Raspberry Pi's website. But they state it "is not for general sale."

Strange times beget strange things.

And that's an apt description of the new Raspberry Pi Compute Module 4S:

The above chart is from Revolution Pi's page announcing the RevPi S and SE, which are updates to their popular CM3+-based industrial DIN rail computers.

A couple months ago, Axzez reached out and asked if I'd like to test out the Interceptor—an ATX-style mini motherboard for the Raspberry Pi Compute Module 4, complete with 5 SATA ports.

The board is meant to be used as an NVR (Network Video Recorder): You pop a Raspberry Pi Compute Module 4 on top, you plug in up to 5 SATA hard drives for storage, and then you plug IP cameras into the 3 extra LAN ports (via an RTL8367RB switch) on the back, and you can store IP camera footage on the drives, and access it over the network.

The internal WiFi module on the Compute Module 4 (that's the bit under the metal shield in the picture above) routes its antenna signal via software. You can route the signal to either:

1. The built-in PCB triangle antenna (this is the default).
2. The external U.FL connector (which has an external antenna plugged into it in the picture above)

To switch the signal to the U.FL connector (for example, if you're installing your CM4 in a metal box where the PCB antenna would be useless), you need to edit the boot config file (sudo nano /boot/firmware/config.txt, and add the following at the bottom:

# Switch to external antenna.
dtparam=ant2

Then reboot the Pi.

Yesterday André Costa emailed me about his new website, rpilocator.

It's a website to track Raspberry Pi 4 model B, Compute Module 4, Pi Zero 2 W, and Pico availability across multiple retailers in different countries.

In his own words:

This database was created out of frustration trying to locate a Raspberry Pi product in the height of the chip and supply chain shortages of 2021. I got tired of visiting multiple websites every day trying to figure out if there were any Raspberry Pi's in stock. I coded this website in a few days during my spare time and had it hosted on a Raspberry Pi for a couple of weeks before deciding to make it publicly available. This is not hosted on a Raspberry Pi anymore.

Earlier this year, I pitted the $549 ASUSTOR Lockerstor 4 NAS against a homebrew $350 Raspberry Pi CM4 NAS, and came to the (rather obvious) conclusion that the Lockerstor was better in almost every regard.

Well, ASUSTOR introduced a new lower-cost NAS, the $329 Drivestor 4 Pro (model AS3304T—pictured above), and sent me one to review against the Raspberry Pi, since it make for a better matchup—both have 4-core ARM CPUs and a more limited PCI Express Gen 2 bus at their heart.

Around the same time, Radxa also sent me their new Taco—a less-than-$100 Raspberry Pi Compute Module 4 carrier board with 5x SATA ports, 1 Gbps and 2.5 Gbps Ethernet, an M.2 NVMe slot, and an M.2 A+E key slot. (The Taco will soon be available as part of a kit with a CM4 and case for around $200.)

The specs evenly matched, at least on paper:

Since the Raspberry Pi was introduced, hundreds of clones have adopted the Pi's form factor (from the diminutive Zero to the 'full size' model B). Often they have better hardware specs, and yet they remain a more obscure also-ran in that generation of Single Board Computer (SBC).

So when I saw Radxa's CM3 and Pine64's SOQuartz, I wanted to see if either would be—as they advertised—'drop in, pin-compatible replacements' for the Raspberry Pi Compute Module 4.

tl;dr: They're not. At least not yet.

Hardware and Specs

Both boards are technically pin-compatible. And both will boot and run (to some extent) on pre-existing Compute Module 4 carrier boards, including Raspberry Pi's official IO Board:

Since the Compute Module 4 came along last year, there have been a few projects that use it that make me do a double-take: They did what with a Pi?

Alftel's Seaberry is a carrier board for the CM4 in the Mini ITX form factor that adds on eleven PCI Express slots:

When I initially reviewed the Compute Module 4 IO Board, I briefly mentioned there's a 4-pin fan connector. It's connected to the Pi's I2C bus using a little PWM chip, the EMC2301.

But wait... what's I2C, what's PWM, and what's so special about a 4-pin fan connector? I'm glad you asked—this post will answer that and show you how you can control a fan connected to the IO Board, like the quiet Noctua NF-P12 pictured above with my IO Board.

If you plug a fan like that into the CM4 IO Board, it will start running full blast, 24x7. If you need that much cooling, that's great, but a lot of times, I don't mind my Pi's CPU getting warmer if it means I can run the fan silent most of the time.