Raspberry Pi 4 won't work with some power cables due to its USB-C design flaw

Did Raspberry Pi Foundation fail to test Raspberry Pi 4 properly? Either way, one expert says new flagship is not USB-C compliant and must be fixed.

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The Raspberry Pi Foundation has confirmed its brand-new Raspberry Pi 4 Model B has a problem with some USB-C cables failing to charge the little computer. 

The Raspberry Pi 4 is the first version to include a USB-C port capable of supplying power to it. The problem, as some early users have found, is that certain charging cables don't work. But they would have if the Raspberry Pi Foundation had simply followed the USB-C specification to the letter. 

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The issue was first reported by Liliputing and has now been confirmed by Raspberry Pi co-founder Eben Upton in a statement to ZDNet sister site TechRepublic

"A smart charger with an e-marked cable will incorrectly identify the Raspberry Pi 4 as an audio adapter accessory and refuse to provide power," says Upton.

"I expect this will be fixed in a future board revision, but for now users will need to apply one of the suggested workarounds. It's surprising this didn't show up in our (quite extensive) field testing program."

The issue was first raised by Tyler Ward, who notes the primary e-marked charging cable that doesn't work with the Raspberry 4's USB-C port is the MacBook charger. Many other cables work just fine. 

Benson Leung, a Google Chrome OS engineer, who's been waging a campaign on shoddy USB-C cables says Raspberry Pi engineers made a "common USB-C hardware design mistake" that makes even compliant USB-C chargers deliver zero volts instead of the 5V needed by the Pi 4. 

Before Upton's statement, Leung had criticized Raspberry Pi makers for appearing to have failed to have done sufficient testing.    

The USB-C specification defines two pins called CC1 and CC2 for connecting to the power sink in a specific way. Leung says Raspberry Pi designers deviated from it in two critical ways. 

"The first is that they designed this circuit themselves, perhaps trying to do something clever with current level detection, but failing to do it right. Instead of trying to come up with some clever circuit, hardware designers should simply copy the figure from the USB-C Spec exactly," wrote Leung. 

"The second mistake is that they didn't actually test their Pi 4 design with advanced cables. I get it, the USB-C cable situation is confusing and messy, and I've covered it in detail that there are numerous different cables," he continued. 

"However, cables with e-marker chips (the kind that would cause problems with Pi 4's mistake) are not that uncommon. Every single Apple MacBook since 2016 has shipped with a cable with an e-marker chip. The fact that no QA team inside Raspberry Pi's organization caught this bug indicates they only tested with one kind (the simplest) of USB-C cable."

Regardless of the amount of testing that was done, Leung called on the foundation to "do better" and correct its design so that it is actually "USB-C compliant".    

The USB-C flaw is the second recent power-related product issue the foundation has created in recent months. 

The company withdrew its PoE (Power over Ethernet) HAT for the then new Pi 3B+ last September over power-supply problems. Back then, Raspberry Pi engineers admitted they'd failed to test the HAT adequately.  

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