Pi Compute Module 4 - Time to Take Industrial Pi Seriously
Written by Harry Fairhead   
Tuesday, 20 October 2020

It's been a long wait, but at last the Raspberry Pi Compute Module 4 is available and it's quite a departure from earlier compute modules. Is this enough to get the Pi a place at the serious IoT table?

The Raspberry Pi 4 is a remarkable bargain, making it possible to contemplate doing things that would otherwise be economically or technically difficult. But the full Pi is often too much for a serious application, and this is where the compute module comes into its own.

The compute module is a cut-down version of the Pi, with a form factor that makes it possible to plug it into a PCB of your own design.

cm4front

Previous compute modules used JEDEC DDR2 SODIMM modules - that is you plugged it in as if it was a memory module. To make use of it you had to design a PCB that accepted the module as it if was memory.

The new compute module has abandoned this approach and instead what you get is a small, credit-card size, module with all of the I/O brought out on two high-density connectors. Your PCB has to allow these to plug in and presumably hold the board with standoffs.

cm4front

cm4back

The other thing that is different is that you can customize the module in terms of the RAM, Flash and wireless. You can have wireless or no wireless, 1, 2, 4 or 8 GBytes of RAM and 0, 8, 16 or 32 GBytes of eMMC storage. A little arithmetic will tell you that this means there are 32 variants. The 1 GByte RAM, no wireless options are priced at $25, $30, $35 and $40 according to the amount of storage, the same as the comparable Compute Module 3. If you opt for everything then you get wirelsss, 8GB RAM and 32GB of onboard storage for $90.

 

The specifications are:

  • 1.5GHz quad-core 64-bit ARM Cortex-A72 CPU
  • VideoCore VI graphics, supporting OpenGL ES 3.x
  • 4Kp60 hardware decode of H.265 (HEVC) video
  • 1080p60 hardware decode, and 1080p30 hardware encode of H.264 (AVC) video
  • Dual HDMI interfaces, at resolutions up to 4K
  • Single-lane PCI Express 2.0 interface
  • Dual MIPI DSI display, and dual MIPI CSI-2 camera interfaces
  • 1GB, 2GB, 4GB or 8GB LPDDR4-3200 SDRAM
  • Optional 8GB, 16GB or 32GB eMMC Flash storage
  • Optional 2.4GHz and 5GHz IEEE 802.11b/g/n/ac wireless LAN and Bluetooth 5.0
  • Gigabit Ethernet PHY with IEEE 1588 support
  • 28 GPIO pins, with up to 6 × UART, 6 × I2C and 5 × SPI

and this makes it a very powerful module.

If you want a development system then there is the I/O board. You plug the module into the $35 board and you have the equivalent of a full Pi 4 plus a real-time clock and some extras. The I/O ports are brought out to external connectors:

  • Two full-size HDMI ports
  • Gigabit Ethernet jack
  • Two USB 2.0 ports
  • MicroSD card socket (only for use with Lite, no-eMMC Compute Module 4 variants)
  • PCI Express Gen 2 x1 socket
  • HAT footprint with 40-pin GPIO connector and PoE header
  • 12V input via barrel jack (supports up to 26V if PCIe unused)
  • Camera and display FPC connectors
  • Real-time clock with battery backup

cm4io

You can also get a KiCad file for the layout to use as a starting point for your own design. Even though this is billed as a development board you might want to use it as a "better" Pi 4 because of its ability to work with different DC Power inputs, a PCI bus and RTC.

So does this make the Pi a contender in the "serious" IoT/ embedded area? It most certainly isn't up to any application that is mission critical. It isn't rugged-ized and it has no redundancy. Any engineer currently involved in that sort of area is going to burst out laughing at the suggestion that the new compute module has anything to offer. However, there is a fairly large area of application that it does suit - anything that isn't mission-critical and needs a display screen and/or a camera and ???processing power of a desktop built into some other device. For this the compute module is looking like an interesting choice with a support community and potential lifetime that would be the envy of any alternative.

  • Harry Fairhead is our resident SBC expert. His acclaimed book on the Raspberry Pi has this month been republished as Raspberry Pi IoT in C, Second Edition  in an updated and expanded edition that now covers the Pi 4.

 

More Information

Raspberry Pi Compute Module 4 on sale now from $25

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Last Updated ( Tuesday, 20 October 2020 )