Ambitious overclocker cools Raspberry Pi 5 with liquid nitrogen

Pi supremo Eben Upton tells El Reg: 'I love this sort of thing'

Updated The dark arts of overclocking remain alive and well. And one master of the practice has turned their attention to the Raspberry Pi 5 with the intention of getting the diminutive computer all the way to 4 Ghz via various exotic and gloriously impractical means.

We asked Pieter-Jan Plaisier of SkatterBencher.com why such a thing should be attempted. He told The Register: "I'm a tech enthusiast and enjoy playing around with all kinds of chips, seeing how [much] performance we can squeeze out of them.

Raspberry Pi 5 cooled by liquid nitrogen (pic: Pieter-Jan Plaisier) – click to enlarge

"Usually that's Intel or AMD CPUs (like getting the 14900K to 9 GHz with liquid helium), but once in a while I like to try something totally different like the Pi 5."

The hope was that the computer could be taken even as far as 5 GHz, but, alas, it was not to be. "I was hoping it would scale like regular desktop chips with lower temperatures and higher voltages, maybe even getting to 5 GHz, but unfortunately got stuck at 3.6 GHz."

It was not, however, for the want of trying. Plaisier had already got the Raspberry Pi 5 to 3 Ghz with a slightly improved cooler. Going further would need some creative thinking and exotic gear, including liquid nitrogen, to cool the hardware.

The first step was to enable NUMA emulation on the Raspberry Pi 5 to bump up the performance in benchmarks. That done, Plaisier then slowly increased the operating frequency to 3,600 MHz before the Pi locked up at 3,700 MHz.

Considering that 3,600 MHz was achieved at ambient temperatures (in this case, approximately 20°C), reducing the temperature should mean higher frequencies could be achieved. But no, even running at -40°C resulted in the same type of crash at the same frequency. Could there be a lack of voltage scaling?

Not to be deterred, Plaisier took the warranty-voiding step of connecting the ElmorLabs AMPLE-X1 power card to the Pi to get better control of the power circuit. This time, he carefully increased the voltage to get a higher frequency, but again, there was no joy. The Raspberry Pi 5 continued to lock up when taken beyond 3,600 MHz.

Ok – so how about changing the crystal oscillator? The Raspberry Pi 5 has a 54 MHz crystal on the board. By applying a bit of heat, the intrepid tech boundary pusher was able to replace it with the ElmorLabs External Clock Board to adjust the input clock higher or lower than the default 54 MHz.

While the input clock wouldn't exceed approximately 56 MHz, Plaisier reported that he could get it down as low as 46 MHz, meaning that the Arm frequency could be set to 4,000 MHz. Success!

Well, not really. Despite Broadcom's tool reporting the frequency as 4,000 MHz, the real frequency was quite a bit lower since the reference clock was lower. According to Plaisier, "The actual frequency is 4,000 / 54 x 46 = 3,407 MHz."

So there you have it. The highest possible frequency for a Raspberry Pi 5, according to Pieter-Jan Plaisier, is currently 3.6 GHz, regardless of exotic cooling methods and warranty-voiding fiddling with voltage and crystals.

It is still an impressive step up from the stock 2.4 GHz Raspberry Pi 5 and a world away from when this writer tried to persuade an Intel 486DX-33 to run a little faster and Doom run a little bit smoother. ®

Updated to add on November 15:

Pi supremo, Eben Upton, told El Reg: "I love this sort of thing."

He said he thought it was "Impressive that they managed to get to 3.6GHz, and you can really see how the NUMA emulation work we've done unlocks much greater linearity in the performance response to frequency increase. These TSMC processes get incredibly bulletproof to overvoltage over time, and 16nm has been around for a while."