Raspberry Pi CM4 launches with smaller footprint, quad -A72 CPU, and optional Wi...

Raspberry Pi CM4 launches with smaller footprint, quad -A72 CPU, and optional WiFi

Oct 19, 2020 — by Eric Brown

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The Raspberry Pi Compute Module 4 starts at $25 with the same quad -A72 SoC as the RPi 4 plus up to 8GB RAM and 32GB eMMC, optional 802.11ac, and support for dual 4K HDMI, GbE, PCIe 2.0, and an optional IO Board.

The Raspberry Pi Foundation is getting ahead of itself. First, there was the surprise Raspberry Pi 4 Model B launch in June 2019 after hints about a 2020 launch, followed by a surprise 8GB RAM RPi 4 model in May of this year. Now, after indications that the Raspberry Pi Compute Module 4 (CM4) would not arrive until 2021, the module has launched starting at the same $25 price, but with up to 8GB RAM and the same Broadcom BCM2711 SoC with 4x 1.5GHz Cortex-A72 cores found on the RPi 4. Earlier Compute Modules topped out at 1GB LPDDR2.

Raspberry Pi Compute Module 4 standard (left) and Lite models
(click images to enlarge)

Compared to the earlier, RPi 3 like Raspberry Pi Compute Module 3 and RPi 3+ like Raspberry Pi Compute Module 3+, the Raspberry Pi Compute Module 4 not only offers a faster processor and faster and more capacious LPDDR4-3200 RAM, but it’s the first with a GbE controller and the first with optional wireless. For an extra $5, you can add 802.11b/g/n/ac and Bluetooth 5.0 BLE plus an optional external antenna.

The Raspberry Pi CM4 is not backward compatible to earlier Compute Module carrier boards. It switches from the SODIMM connector of the CM3+, CM3, and original Arm11-based CM1 to dual, high-density, 100-pin perpendicular connectors — one for power and low-speed interfaces found on the CM3/CM3+ and one for high-speed interfaces like PCIe. This enables a smaller 55 x 40 x 4.7mm footprint compared to the earlier 67.6 x 31mm.

To support the new form factor, RPi Trading has launched an updated RPi Compute Module IO Board carrier. The IO Board is designed not only for prototyping but for field deployment as a sandwich style alternative to an RPi 4 SBC (see farther below).

Raspberry Pi CM4 rear view showing low- and high-speed B2B connectors (left) and pricing list
(click images to enlarge)

With all the different RAM, eMMC, and wireless options, there are 32 SKUs available. The four variants with 1GB RAM and no wireless stay the same: $25 for the Lite model without eMMC, as well as $30 (8GB eMMC), $35 (16GB), and $40 (32GB). A maxed-out model with 8GB RAM, 32GB, and wireless costs $90.

The Wireless module, which includes an onboard antenna, adds only $5 to any configuration (see diagram above). Modular wireless compliance certification is available.

The Raspberry Pi CM4’s Broadcom BCM2711 integrates the same VideoCore VI graphics with OpenGL ES 3.x support. The CM4 supports 4Kp60 hardware decode of H.265 (HEVC), 1080p60 hardware decode, and 1080p30 hardware encode of H.264 (AVC) video. Like the RPi4 it supports dual HDMI ports and offers 2x and 4x MIPI-DSI and -CSI interfaces.

The CM4 is further equipped with a PCIe x1 Gen2 interface. On the RPi 4 this is dedicated to USB 3.0 and it requires some hacking to free it up to run another PCIe peripheral such as NVMe. Here, you are sacrificing USB 3.0 to get PCIe, but there is a USB 2.0 host port with hub support. The eMMC-less Lite model offers an SDIO 2.0 connection. A Broadcom BCM54210PE Gigabit Ethernet controller supports IEEE 1588.

Closeup on CM4 high-speed interface (left) and IO Board
(click images to enlarge)

A 28-pin GPIO interface provides up to 6x UART, 6x I2C, 5x SPI, 2x PWM, 3× GPCLK outputs, and single SDIO DPI (Parallel RGB Display) and PCM. You can choose either 1.8v or 3.3v modes. The 5V DC powered module supports 0 to 80°C operation and offers availability through 2028.

An optional, $5 Compute Module 4 Antenna Kit is available for scenarios such as usage within a metal case that might block the internal antenna. The kit comprises a whip antenna with a bulkhead screw fixture and U.FL connector.

Compute Module 4 IO Board

The optional, $35 IO Board is the first such carrier board for the Compute Module that can be considered “finished product in its own right” in addition to acting as a dev board and reference design. One might consider it for deployment over the Raspberry Pi 4 SBC if you’re looking for full-sized HDMI ports, a wider input range, single-side coastline I/O, and a PCIe x1 Gen2 socket, says Raspberry Pi Trading.

Compute Module 4 IO Board render
(click image to enlarge)

The RPi CM4 IO Board is the first IO Board model equipped with 40-pin GPIO. There are also a lot more coastline ports that the previous model, which was limited to micro-USB and microSD interfaces. The IO Board is equipped with 2x HDMI and 2x USB 2.0 ports with 2x additional headers to provide a four-port hub. Othere features include a micro-USB device port and a single GbE port with a PoE header that supports the Raspberry Pi PoE HAT.

The microSD slot works only with the Lite CM4 model. Other features include MIPI camera and display FPC connectors, an RTC with battery backup, and a fan header. A 12V jack with 5V converter supports a 7-26V range — as long as you’re not using the PCIe and fan interfaces. To ease the development of custom carrier board designs, the IO Board ships with files for the open-source KiCad PCB layout package.

Raspberry Pi Compute Module 4 on YouTube

Further information

The Raspberry Pi Compute Module 4 is available now ranging from $25 to $90 (see pricing chart above). Only a few of the SKUs were available at publication time through resellers such as CanaKit. The IO Board costs $35 without a CM4 module. More information may be found in the Raspberry Pi Blog announcement and CM4 product page with links to shopping and additional documentation.