Everything is a timer

write-upsystems · 19 points · 13 comments

Coming from web to embedded, the thing that took longest to internalise is that there is no event loop coming to save you.

A button press is a timer sampling a pin. A network packet is a timer draining a buffer. Once you stop looking for callbacks and start looking for the clock, the datasheets get much easier to read.

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13 comments

2026-10-14
Worth adding that this only holds if the clock is monotonic. Ours was not, and the failure looked exactly like a slow disk.
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2026-10-14
I have hit this and solved it the other way, and I now think your way is better.
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2026-10-14
Do you have a link for the second claim? I want to read the original.
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2026-10-14
Two years ago I would have argued. Having since maintained one of these, I would not.
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2026-10-14
The part people skip is the last paragraph, which is the whole argument.
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2026-10-14
Counterexample: on a read-heavy workload we measured the opposite. Happy to write it up if useful.
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2026-10-14
Reading this made me go and check ours, and ours was wrong. So: thank you, and also, ugh.
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2026-10-14
What did you use to measure it?
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2026-10-14
A trace, not a profiler. The profiler said the function was fast, which it was.
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2026-10-14
This matches what the errata says, which almost nobody reads.
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2026-10-14
Filed under things I will rediscover in eighteen months and be annoyed about.
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2026-10-14
The naming point generalises. Half our bugs are a name answering a different question than its value.
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2026-10-14
Is there a version of this that works when the window is not fixed?
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