[Development] modbus over serial port on windows 7 ?

Alexander Blasche alexander.blasche at qt.io
Thu Jun 2 13:42:27 CEST 2016

> -----Original Message-----
> From: Development [mailto:development-
> bounces+alexander.blasche=qt.io at qt-project.org] On Behalf Of Denis Shienkov
> Sent: Thursday, 2 June 2016 7:11
> To: development at qt-project.org
> Subject: Re: [Development] modbus over serial port on windows 7 ?
> > only the value of around 50ms gives a stable result in my case.
> Hehh.. I warned the QtSerialBus team that introduction of 3.5 timeouts will lead
> to bugs and that it doesn't make sense (though, it is described in the Modbus
> specification).

> We do not need to rely on this 'characters timeouts', because the
> OS can not provide this precision timeout (besides, Qt5 event loop introduces
> also an delay). But, nobody haven't listened to me.

Denis, that's a nice simplistic viewpoint but does not work for Modbus and comments like the above do not help either. 
Certain error cases can only be detected if you make assumptions about timeouts. Otherwise there is no way to determine where one packet stops and where the next one begins. We are dealing with contradicting requirements on protocol and OS level.

Obviously the current point is not optimal. We have to tweak more. Let's see what we can manage in QTBUG-53767. Please shift this discussion to the bug now. Thank you.


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