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Comment by zootboy | Hacker News Reader

Indeed. I've been building systems that orchestrate batteries and power sources. Turns out, it's a difficult problem to temporally align data points produced by separate components that don't share any sort of common clock source. Just take the latest power supply current reading and subtract the latest battery current reading to get load current? Oops, they don't line up, and now you get bizarre values (like negative load power) when there's a fast load transient.

Even more fun when multiple devices share a single communication bus, so you're basically guaranteed to not get temporally-aligned readings from all of the devices.

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I run a small SaaS side hustle where the core value proposition of the product - at least what got us our first customers, even if they did not realize what was happening under the hood - is, essentially, an implementation of NTP running over HTTPS that can be run on some odd devices and sync those devices to mobile phones via a front end app and backend server. There’s some other CMS stuff that makes it easy for the various customers to serve their content to their customers’ devices, but at the end of the day our core trade secret is just using a roll-your-own NTP implementation… I love how NTP is just the tip of the iceberg when it comes to the wicked problem of aligning clocks. This is all just to say - I feel your pain, but also not really since it sounds like you are dealing with higher precision and greater challenges than I ever had to!

Here’s a great podcast on the topic which you will surely like!

https://signalsandthreads.com/clock-synchronization/

And a related HN thread in case you missed it:

https://news.ycombinator.com/item?id=39298652

The ultimate frustration is when you have no real ability to fix the core problem. NTP (and its 'roided-up cousin PTP) are great, but they require a degree of control and influence over the end devices that I just don't have. No amount of pleading will get a battery vendor to implement NTP in their BMS firmware, and I don't have nearly enough stacks of cash to wave around to commission a custom firmware. So I'm pretty much stuck with the "black box cat herding" technique of interoperation.

Yeah, that makes sense. We are lucky in that we get to deploy our code to the devices. It’s not really “embedded” in the sense most people use as these are essentially sandboxed Linux devices that only run applications written in a programming language specific to these devices which is similar to Lua/python but the scripts get turned into byte code at boot IIRC, but none the less very powerful/fast.

You work on BMS stuff? That’s cool- a little bit outside my domain (I do energy modeling research for buildings) but have been to some fun talks semi-recently about BMs/BAS/telemetry in buildings etc. The whole landscape seems like a real mess there.

FYI that podcast I linked has some interesting discussion about some issues with PTP over NTP- worth listening to for sure.

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