Raspberry Pi admits defective USB-C design of Pi 4 is faulty

The Raspberry Pi 4 was announced two weeks ago as a major new upgrade of the computer range to a single inexpensive computer. The Pi 4 featured a faster processor, options for 4GB RAM, and a new modern USB-C port for power delivery. The Pi 4 was the very first USB-C device from the Raspberry Pi Foundation and, well, they ruined everything.

As Tyler Ward explained, the Raspberry Pi 4 has a non-compliant USB-C charging port and does not work with as many chargers as it should. Thanks to the open nature of Raspberry Pi (even the diagrams are online!), Ward discovered that Raspberry Pi simply did not design its USB-C port properly. Two "DC" pins on a USB-C port are supposed to each have their own 5.1K ohm resistor, but Raspberry Pi has created its own circuit that allows you to share a single resistor. This design does not comply and breaks compatibility with some of the most powerful USB-C chargers.

Whether your USB-C charger works with the Pi 4 depends on whether or not a cable marked "e". The cables marked E are USB-C cables complete with chips inside that negotiate power management, accessory modes, data rates and other communication specifications. As the Pi 4 USB-C port is badly wired, these smart cables will detect the Pi 4 as an "audio adapter accessory" and will refuse to charge it. As a general rule, cables with the e symbol are more expensive and come with larger, more powerful components, such as a USB-C laptop.

Benson Leung, an engineer at Google and one of the world's foremost experts in USB-C implementation, is also inspired by the Pi4's USB-C design, with a Medium article titled "How to design a appropriate USB-C ™ skylights (hint, not like Raspberry Pi 4 did). "

"Instead of trying to design a smart circuit," Leung writes, "hardware designers should simply copy the figure of the USB-C specification exactly [emphasis his]. Figure 4-9 that I posted above is not just a rough indication of how to make a USB-C receptacle. It's done normative, which means mandatory, required by the specification to call your system a USB-C compliant power sink. Just copy it. "

The Pi 4 is not the first high-end device to go wrong with USB-C specification. The Nintendo switch also has a non-compliant USB-C port and has problems with some USB-C cables.

After reports began to appear on the Internet, Raspberry Pi's co-founder, Eben Upton, admitted to TechRepublic that a "smart charger with a marked cable" would incorrectly identify the Raspberry Pi 4 as "unauthorized". audio adapter accessory and would refuse to provide power. " Upton added, "I guess this will be resolved in a future board review, but for now, users will need to implement one of the suggested workarounds." It's surprising that this has not appeared in our program field test (quite extensive). "

The "suggested workarounds" simply involve using an unlabeled cable e, such as the official Pi 4 charger.

We contacted Raspberry Pi about this problem and were told that a revision of the card with a loading port compliant with the specifications should be published in the "coming months".