Pi 5 overclocking: Silicon Lottery

That sounds like a lot of fun. Do you happen to have any photos of you tinkering especially with the 10-LED bar temp displays?

I remember overclocking my calculator (TI-85, 1992, Z80 CPU) ... its LO was a 2.7K/22pF RC oscillator which gave it an approximately 2.5MHz clock. To get this type of oscillator to speed up you'd normally lower the capacitance a bit.

The reason that this story is interesting is that in most cases you could just yank C9 entirely and with nothing more than a resistor between the clock pins, you'd get a roughly 300% performance increase. I guess the parasitic capacitance was enough to still oscillate a bit although mostly it would have been random. Looking back, this was basically a CPU being clocked with 50mhz noise and still running happily! Amazing!

I have a ST486-DX2-66GS (1998), and I found it is unstable at the stock 66MHz. I actually have to run it at 80MHz to prevent random freezes.

That was before binning really got to be a business model. Of course once a production line was stable, they could generate more high end chips than they actually needed, and so the chip you bought from bin 3 might actually be a bin 2 chip. It always seemed like AMD was really conservative that way, which is why hobbyists loved them.

I have a recollection of a guy who got a 486 DX-33 up to 133 MHz by putting the entire computer in mineral oil and floating chunks of dry ice in it. Watch out for asphyxiation.

Of course! These are like BGA or something similar, the solder will crack after some number of on/off/cool/heat cycles.

If voltage is raised we enter the realm of electromigration, though not sure how relevant it is for such a minuscule OC.

As for stability, yes. If the voltage is not sufficient there will be stability issues which will require further raising it, thus raising temps and requiring more power which you can't be sure if you could deliver. And then of course electromigration.

Unfortunately, most of the useful data you want about wearout is locked behind tech NDAs so nobody will be able to offer specifics here.

But in general, the way you tend to end up with wearout is through electron migration ("electron wind") which is damage to interconnects from electrons slamming into metal atoms over and over and slowly ripping apart the wires. Modeling electron migration correctly is really hard, but (from memory) a general relationship is that voltage linearly increases failure rate and temperature exponentially increases it. The constants for these models are determined empirically and, of course, are NDA'd.

In general, I wouldn't worry about it. The MTTF for semiconductors is already very high even under awful temperatures 100+ C, and so as long as you cool it properly you'll be fine.

> would it be expected that a non-zero amount would fail?

The failures you describe here are going to be due to setup time violations. These issues shouldn't be transient (assuming identical temperature and voltage) since the performance characteristics of an individual device don't really change over time. Of course, the issues can seem transient as the failures may not actually always cause noticeable corruption (maybe you generate a wrong FPU result but that specific path is only exercised under rare uarch conditions).

So, it's a non-answer, but: yes and no. Maybe your chip is perfectly okay and never has any violations at the parameters you selected. Maybe it does. Neither you (nor in fact the manufacturer, though they do have a better chance since they know the process/design) can ever really be sure--all that's left is empirical burn in testing and hoping for the best :)

From what I remember from school, the extremely rough rule of thumb, specifically for thermal effects on the silicon itself, is that +10C will halve the lifespan of the chip. When you try to push a chip with an OC, the power/perf gets highly nonlinear, so you end up making tradeoffs here. Chip vendors like Intel and AMD do a lot of testing and validation to pick power curves that will meet the warranty specs of the chip, but they do have some wiggle room.

There’s a whole bunch of other failure modes that aren’t captured by the 10C rule. It’s more for estimating chip failure due to things like electromigration. You can observe this if you run a desktop CPU overclocked for many years. I had a 2600k that I had to keep bumping the OC down on, and jt eventually bit the dust after a decade.

My experience with running GPUs is that overclocking tends to go with undervolting and it has zero impact on longevity of the chips themselves. Other components like power supplies, with consumable or hand made things, like hand soldered components, are what end up failing.

We had cards in the worst of the worst environments and they ran fine for years on end.

Radxa Rock 5 model B, Turing Pi RK1, Orange Pi 5 (and Plus); there are a few others but those are the models I have purchased and tested. All are more efficient/faster... but also more expensive and less supported. Though RK3599 and 3588 SoCs have both been some of the most widely supported out of Rockchip for Linux applications. They still lack compared to Pi's support though.

I ordered one from pishop.us just last Friday that arrived via USPS on Monday morning. Might look around some and see if you can just order from a different vendor.

They've been on the shelf (well, behind the counter) at Micro Center for a month or so now, never seen them out of stock. It seems like all the models are available at one or two retailers at minimum now, via rpilocator.com.

Are you in the US, Canada, or EU? Outside of those places, there may still be some delays in getting stock to meet demand.

Oof, $80 is encroaching on Aliexpress N100 Mini PCs and used "Tiny/Mini/Micro" territory.

I have the original and updated Pi Zero W-- unbelievable bargains at ~$15 but if I needed any horsepower I think I'd rather have an x86_64 so I can run whatever.

You know, he has a video on that too. If you want GPIO, a tiny PC is not the answer (for example).

Mini PCs don't come with GPIOs, which are one of the main reasons that make small SBCs a better choice for some uses. Not a big problem though as there are cheap add on boards bringing GPIO ports to every device. Example: https://www.hardkernel.com/shop/usb-io-board/

The downside is that code becomes slightly more complicated, the upside is that it makes easier to replace the Mini PC with a totally different one, or even emulate it in a VM then connecting the GPIO board using USB pass through.

Rethinking GPIO can also open more possibilities such as putting them beyond a network (say Arduino+ENC28j60 and similar ones for Ethernet, ESP32 for wireless, etc); of course having them outside the main CPU will imply some speed and latency issues, although I'm sure they would remain unnoticed for many non critical use cases.

My question would rather be why the RPi when there are better SBCs out there, but that is my personal taste and the Armbian and DietPi communities being more than enough for me.

I recently went on the lookout for this board and it is still unavailable. All I could find were M.2 adapters. I guess the market for full-size PCIe is tiny compared to the M.2 one.

Anyways, I ended up making my own and it works great. No fuss, no wait, no complications.

I keep pushing Pineberry Pi to release that—apparently they're still working on it—and 52Pi pre-announced something too...

But so far there's no straight PCIe expansion board available to purchase yet. It is a slimmer market than 'NVMe on top' or other more standard use cases, but it's one I think could expand as people do weird things with the Pi 5.