[OpenTRV-dev] Puzzling long-term bugs

Kevin Wood kevin at the-wood-family.com
Thu Sep 29 09:39:01 BST 2016

Hi Damon,

If it's the RC oscillator then it will be far enough out to cause issues
on long blocks of data in my experience.

I'm not sure why this is a problem. As you say, it SHOULD be possible for
the receiving UART to resync on every start bit, or, in fact, on every
transition of the signal. The fact is that they don't appear to do so
except on a start bit after the link has fallen idle, or, at least, the
typical PC COM port or USB-to-Serial adaptor doesn't.

Maybe the AVR's UART is more intelligent in this respect, and this is why
we are not seeing corruption on firmware loads, since it's then the PC
that is transmitting flat-out?

Best Regards


> Hi,
> The UART clocks being out relative to one another is in my view quite
> likely an issue since on our board’s side the clock is derived from the
> AVR’s 8MHz internal RC clock.
> This does mainly seem to be an issue with solid blocks of characters (eg
> ~16 or more bytes) being sent at once (to the AVR board), though I would
> expect everything to resync on each start bit.
> I don’t believe any buffers are being overwritten since we are using the
> normal Arduino queued serial byte streams, with everything interrupt
> driven, though that may be worth another look, thank you.
> Puzzling!
> Rgds
> Damon
>> On 28 Sep 2016, at 17:11, Jeremy Poulter <jeremy at bigjungle.net> wrote:
>> Is this more than just UART being UART and the clocks of of each side
>> being out?
>> Maybe try repeatedly sending 'U' on one of the problematic devices and
>> measure the frequency, should be half the baud rate as U is 01010101
>> IIRC you use a relatively slow baud rate (4800 IIRC) so you could be
>> overwriting data in a buffer if you send data to fast?
>> Jeremy
>> On 28 Sep 2016 3:08 p.m., "Damon Hart-Davis" <damon at opentrv.uk> wrote:
>> Hi,
>> We have a Wiki page here for our general amusement:
>> https://github.com/opentrv/OTWiki/wiki/Puzzling-Long-Term-Bugs
>> We’ve certainly been having some puzzlement while putting together a
>> small run of valves for a trial over the last few days.  Could be
>> summarised as ‘dodgy serial’:
>> - Some REV7 and other V0p2 units seem to have problems with serial RX
>> and TX, garbling some characters
>>     - Seems especially problematic for longer (16+?) blocks of
>> characters such as setting a key
>>     - Have tried to ensure no sleeping or other fiddling with CPU clock
>> during UART operation
>>     - Seems to apply to a few % of REV7, REV10 boards at least
>>     - It has been possible to load a large (30KB) app over serial with
>> the bootloader.
>> Any ideas welcome!
>> Rgds
>> Damon
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