Unveiling the Raspberry Pi CM0: A Compact, China-Exclusive Compute Module

The Raspberry Pi CM0 is a remarkably compact Compute Module, effectively a full Raspberry Pi Zero 2 packed onto a board the size of a postage stamp, complete with integrated eMMC storage and Wi-Fi. Despite its advanced features for its size, global access remains limited, primarily available through EDAtec's CM0NANO development board or within China.

Compute Modules are distinct from standard Raspberry Pi boards. These "System on Modules" (SoMs) are self-contained Linux computers, roughly the size of a desktop CPU, designed to be integrated into custom carrier boards. They are widely used in industrial applications such as kiosks, digital signage, 3D printers, and even audio equipment, serving as an ideal solution for networking and remote control where a small Linux footprint is required. The CM0 represents the smallest iteration in this Compute Module line.

A key differentiator for the CM0 is its castellated edges, reminiscent of a Raspberry Pi Pico. This design facilitates direct surface-mount soldering onto a product's main PCB, offering a more robust and streamlined integration method compared to the delicate board-to-board connectors typically used with other Compute Modules.

To aid development, EDAtec provides the CM0NANO IO board, which serves as an official development platform for the CM0. This board breaks out all features of the core RP3A0 chip, including 10/100 Ethernet (via a USB to Ethernet chip), two USB 2.0 ports, a full-size HDMI output, and a USB-C port for power and eMMC flashing. It also includes connectors for display, camera, and GPIO.

Flashing the onboard eMMC requires setting the RPI_BOOT_SW switch and using rpiboot to mount the storage, after which standard tools like Raspberry Pi Imager can be used. Performance-wise, the eMMC on the CM0 is relatively slow, achieving speeds around 19-20 MB/sec, which is significantly lower than more recent Pi generations. Once flashed, the CM0 runs a full Linux computer environment, typically with Raspberry Pi OS. EDAtec offers a firmware support package for further optimization.

While powerful for embedded tasks, the CM0's limited 512MB of RAM makes resource-intensive applications, such as web browsing with Chromium, impractical. Chromium itself issues a warning, recommending at least 1GB of RAM. However, for products that need a well-supported Linux environment with integrated Wi-Fi, Ethernet, USB, and HDMI, without the complexity of designing an entire SoC, memory, storage, and wireless solution from scratch, the CM0 presents a compelling option.

The restricted global availability of the CM0 is a significant point of discussion. The Raspberry Pi Zero 2 W and the CM0 share their underlying architecture and have both been impacted by global supply chain challenges. The Zero 2 W was released during a period of widespread chip shortages, while the CM0's introduction coincided with severe RAM shortages. The core issue for the CM0 lies with the RP3A0 chip, which integrates an LPDDR2 RAM chip stacked atop the Pi's SoC. LPDDR2 memory is increasingly scarce as production has ceased, making existing stock finite. Raspberry Pi aims to prioritize the popular Zero 2 W for makers and education, meaning the CM0, targeted at the lower-end integrated product market, is unlikely to see broad distribution outside of China.

Given its close resemblance to the Raspberry Pi Zero 2 W and its limited availability, a comprehensive standalone review of the CM0 is less critical. For the foreseeable future, those outside China should continue to rely on the more accessible Pi Zero 2 models.