[OpenTRV-dev] AVR (328P) EEPROM puzzler

Damon Hart-Davis damon at opentrv.uk
Sun Mar 20 07:25:44 GMT 2016

I have posted a question on the Arduino forum here:




> On 18 Mar 2016, at 20:12, Damon Hart-Davis <damon at opentrv.uk> wrote:
> Hi,
> We are seeing some bizarre behaviour where when we try to write a 16-byte key into EEPROM it fails to ‘stick’ properly the first time.  If the board is power-cycled and the key is written again, it appears to stick as expected.  (There’s some subtle sub-wierdnesses also.)  This uses some ‘careful’ update routines that we use extensively elsewhere and seem to be fine with blocks as large as 8 bytes long (node IDs).
> Lots of use of my favourite search engine is failing to show any evidence of this being a common problem.
> I have reviewed the code repeatedly and found a minor wrinkle which is merely an inefficiency, not an error.
> Anyone fancy doing some detective work and then pointing out exactly why I shouldn’t be allowed near a keyboard any more?  B^>
> Rgds
> Damon
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