sbc

I'm in the unique position of owning a collection of Raspberry Pi Compute Modules 4 (CM4).

I also own at least one of every production CM4 clone in existence.

This sets up a quandary: if I have the real thing, what motivation do I have to care about the clones?

There are hundreds of CM4 carrier boards that do everything from restoring retro game consoles to monitoring remote oil rigs in highly-explosive environments.

Since launch, the CM4 has been difficult—and since early 2021, impossible—to acquire. The supply constraints are well documented, and I'm sure a few comments will lament the situation. But the CM4 is trickling back to 'in stock' at many suppliers (about how the Pi 4 was a couple months ago).

tl;dr: No, it's not a replacement for a Raspberry Pi Compute Module 4. But yes, it's an exciting tiny RISC-V board that could be just the ticket for more RISC-V projects, tapping into the diverse ecosystem of existing Compute Module 4 boards.

This tiny computer is the Mars CM. It's the exact same size and shape as the Raspberry Pi Compute Module 4. It should be a drop-in replacement. And on its box it says it supports 4K, Bluetooth and WiFi, and has gigabit Ethernet. It's also supposed to have PCI Express!

In my video about the brand new Raspberry Pi 5, I mentioned the new external PCIe port makes it possible to boot the standard Pi 5 model B directly off NVMe storage—an option which is much faster and more reliable than standard microSD storage (even with industrial-rated cards!).

Enabling NVMe boot is pretty easy, you add a line to /boot/firmware/config.txt, modify the BOOT_ORDER in the bootloader configuration, and reboot!

If you haven't heard, the Raspberry Pi 5 was announced today (it'll be available in October).

I have a full video going over the hardware—what's changed, what's new, and what's gone—and I've embedded it below. Scroll beyond to read more about specs, quirks, and some of the things I learned testing a dozen or so PCIe devices with it.

Earlier this month, I was able to discuss with Eben Upton (co-founder of Raspberry Pi) the role RISC-V could play in Raspberry Pi's future (among other things—watch the full interview here).

Radxa's Rock 5 model B is an ARM single board computer that's 3x faster than a Raspberry Pi. And that's just the 8-core CPU—with PCI Express Gen 3 x4 (the Pi has Gen 2 x1), storage is 7x faster! I got over 3 GB/sec with a KIOXIA XG6 NVMe SSD.

It's still half as slow as modern ARM desktops like Apple's M1 mini, or Microsoft's Dev Kit 2023 (see my review here). But it's way faster than a Pi, it comes with 2.5 Gig Ethernet, it has two M.2 slots on board... and, well—it also starts at $150!

For many years, I've maintained some scripts to do basic disk benchmarking for SBCs, to test 1M and 4K sequential and random access speeds, since those are the two most relevant tests for the Linux workloads I run on my Pis.

I've been using this script for years, and it uses fio and iozone to get the metrics I need.

And from time to time, I would test a number of microSD cards on the Pi, or run tests on NVMe SSDs on the Pi, Rock 5 model B, or other SBCs. But my results were usually geared towards a single blog post or a video project.

In 2021 James Chambers set up PiBenchmarks to move to a more community-driven testing dataset.

You can run the following command on your SBC to test the boot storage and upload results directly to PiBenchmarks.com:

...or at least, not without a lot of patience or a fat wallet.

But why? And are there any signs Raspberry Pis will become available to the general public again soon?

To be clear, I'm speaking of the mainstream SBC Raspberry Pis, like the Pi 4 model B, the Compute Module 4, the Pi Zero 2 W, and even in many cases the Pi 400. The Pico and Pico W are both readily available, at least in most markets where I've looked (local shortages always exist, but typically not for months or years like with full-size Pis).

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:

I recently got an Nvidia Jetson Nano 2GB Developer Kit, and I read through and followed the Developer Kit Getting Started Guide straight from Nvidia's website.

I downloaded the 7 GB(!) microSD card from their website, and flashed it to a 128 GB microSD card using Balena Etcher.

Then I popped the microSD card into my dev kit board, plugged in HDMI and a USB-C 3A power supply, and waited... I kept seeing a giant NVIDIA logo on my display, and after about 20 seconds, it would seemingly reboot to black screen, then the logo... and repeat forever.

Searching around the Nvidia forums, I eventually found this issue: Nano 2GB boot looping, and finally found the problem: apparently the default image download is only for the 4GB Nano model.