Raspberry Pi Pico 2 at 873.5MHz with 3.05V Core Abuse

Great stuff.

It wouldn't be surprising if the RP2350 gets officially certified to run at something above the max supported clock at launch (150MHz), though obviously nothing close to 800MHz. That happened to the RP2040[1], which at launch nominally supported 133MHz but now it's up to 200MHz (the SDK still defaults to 125MHz for compatibility, but getting 200MHz is as simple as toggling a config flag[2]).

[1] https://www.tomshardware.com/raspberry-pi/the-raspberry-pi-p...

[2] https://github.com/raspberrypi/pico-sdk/releases/tag/2.1.1

When pushing clock speeds, things get nondeterministic...

Here is an idea for a CPU designer...

Observe that you can get way more performance (increased clock speed) or more performance per watt (lower core voltage) if you are happy to lose reliability.

Also observe that many CPU's do superscalar out of order execution, which requires having the ability to backtrack, and this is normally implemented with a queue and a 'commit' phase.

Finally, observe that verifying this commit queue is a fully parallel operation, and therefore can be checked slower and in a more power efficient way.

So, here's the idea. You run a blazing fast superscalar CPU, well past the safe clock speed limits that makes hundreds of computation or flow control mistakes per second. You have slow but parallel verification circuitry to verify the execution trace. Whenever a mistake is made, you put a pipeline bubble in the main CPU, clear the commit queue, you put in the correct result from the verification system, and continue - just like you would with a branch misprediction.

This happening a few hundred times per second will have a negligible impact on performance. (consider 100 cycles 'reset' penalty, 100*100 is a tiny fraction of 4Ghz)

The main fast CPU could also make deliberate mistakes - for example assuming floats aren't NaN, assuming division won't be by zero, etc. Trimming off rarely used logic makes the core smaller, making it easier to make it even faster or more power efficient (since wire length determines power consumption per bit).

As we become acclimated to non deterministic responses from computers it may not even matter if some of that comes from the hardware.

Eventually it will be seen as a feature.

Both the RP2040 and the RP2350 are amazing value these days with most other electronics increasing in price. Plus you can run FUZIX on them for the UNIX feel.

It’s amusing to contemplate energy per cycle as one clocks higher and higher — the usual formula has the energy per cycle scaling roughly as voltage squared.

I recently turned turbo off on a small, lightly loaded Intel server. This reduced power by about a factor of 2, core temperature by 30-40C, and allowed running the fans much quieter. I’m baffled as to why the CPU didn’t do this on its own. (Apple gets these details right. Intel, not so much.)

What I love of the Pico overclock story is that, sure, not at 870Mhz, but otherwise you basically give for granted that at 300Mhz and without any cooling it is rock solid, and many units at 400Mhz too.

it might actually be better to cool from the bottom, since the pads probably conduct heat better than the chip package material

I bet if you designed a custom board it could do a little better

Haha — this was a fun day! It's honestly surprising how robust the RP2350 was under such extreme experimentation. Mike's write-up walks through pushing the core voltages far beyond stock limits and dry-ice cooling to see what the silicon could handle.

Credit where it's due: Mike is a wizard. He's been involved in some of our more adventurous tinkering, and his input on the more complex areas of our product software has been invaluable. Check out his GitHub for some really interesting projects: https://github.com/MichaelBell

Blatant plug: We have a wide range of boards based on the RP2350 for all sorts of projects! https://shop.pimoroni.com/collections/pico :-)

remembering pushing i7 920 on dry ice with acetone by the time... also voltmod nforce 2 chipset to cranck bus clock for opteron 144. So cool !

This some harmless stupid fun.

Interesting post. Curious what can I run on a RPi Pico 2 W since I recently got my hands on it.

Well, hope no one tries to deploy overlocked Raspberry Pi hardware in production... especially for kiosk style applications where they're in a metal box in the sun.

They're unstable enough at stock if taken outside an air conditioned room.