On 2/8/14, 5:06 AM, William "Chops" Westfield wrote:
>> I guess you are not using Modbus over RS485 or RS232? Continuous
>> stream of data and 3.5 character silence to mark end of frame.
> That's horrible.  I suspect that most modern windows systems can't do tha=
t reliably even without virtualization (based on the UART WITH DEEP FIFO ca=
rds that started appearing "for free" with 115kbps external modems, because=
 windows latency was such that otherwise data would be lost OFTEN (implying=
 OS latency of > 2 character times in servicing interrupts.  And that was i=
n W3.1 days; I doubt that worst case latency has gotten better=85)
>
>
>> What's the saying?  Accept widely...
> "be conservative in what you do, be liberal in what you accept from other=
s."
> First appeared in the TCP specification, I think:  http://en.wikipedia.or=
g/wiki/Robustness_principle
>
> BillW
>
>
One client of mine developed a serial port driver specifically to get=20
the MODBUS timing (and another 9-bit protocol with tight timing=20
constraints) handled at the kernel level.

Of course it didn't work for USB to serial devices... and they had to=20
revalidate and tweak it with every OS from Win2K up.


Darron

--=20
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