You've examined the costs, but what about the benefits?

There's only a narrow area where a simple checksum misses an error that a
CRC would catch.

What error rates do you expect?   Most digital connections don't make
errors, and when they do, the term "noise" often means "I haven't taken the
trouble to find out what the problem is".    Now, when there's an analog
link (telephone, radio, modem), then a CRC is a very good idea.  I can see
that a scheme which times the width of pulses might be counted as "analog"
and therefore subject to jitter, aka, noise.

What is the risk of a bad download?  Medical devices, certainly you demand
liability.  Lab experiments and consumer toys, not so important. Maybe once
in its lifetime there will be a bad load, and trying the download again
will fix it.  Which sounds an awful lot like your failure scenario with CRC
anyway :)

Barry
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