Ancestors

Written by Attie Grande on 2025-01-23 at 23:57

I was just reminded of an "implicit communication" story... I love communication as a topic.

While talking with a customer, they told me that "long ago", someone at the top of the company decided that producing an ASIC for their product was a sensible route (🥴). They specified a "32kHz" input to an oscillator that would ultimately do things like track time (i.e: RTC).

Once they received the first silicon back (💰💰📅), they put it on a PCB, and couldn't figure out why it wouldn't keep time.

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Written by Attie Grande on 2025-01-24 at 00:03

Sure enough, after some back and forth, it turned out that the ASIC design team had opted for a 32.000kHz counter feeding the RTC.

My customer had just assumed that 32kHz means 32.768kHz, and had thus placed a 32.768kHz crystal next to their shiny new ASIC.

So the RTC ran at +2.4% (i.e: ~34m 33s 600ms fast PER DAY)

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Written by Attie Grande on 2025-01-24 at 00:05

IIRC, the extra kicker was that they couldn't actually use a 32.000kHz crystal or a 32.768kHz crystal because the one oscillator fed a series of modules, and different branches of the clock tree assumed one or other frequency.

... along the lines of, you can have an accurate RTC, or accurate timing for the field bus, but not both.

Let it be a lesson! 🤷‍♀️

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Toot

Written by Attie Grande on 2025-01-24 at 00:10

... that said, I wish I had time on my hands to participate in the Tiny Tapeout shuttles!

I did get myself a little momento because it's an awesome project though.

Maybe one day. 🤞

https://store.tinytapeout.com/products/Bare-die-cast-in-resin-MPW5-p716799292

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Descendants

Written by Richard Hendricks on 2025-01-24 at 00:19

@attie I had to gently explain to a customer once that the 50ppm accuracy of the 32.768 kHz crystal means that yes, you are going to be +- 2 minutes off every month.

We had a calibration adjustment process to get that down to a few seconds, but they forgot to do it. :blob_cat_ohnoes:

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