Overrun error (-10738072​52) occurs after several minutes

Question

Hello folks,
I have a LV 7.0 program that terminates after several minutes of running with some VISA serial port communication with an error -1073807252, overrun error. I only get this error on Win98 and the latest version of LV (7.0) and VISA (3.01). Does anyone know what exactly causes this error? The help on the error is not very detailed. I tried the same program on a Win2000 PC and it works without any problems. I also tried another VISA communication program on the Win98 PC and the same error occurs.
Thanks in advance,
Michael

Answer 1

Dave,
not really a solution, but a suggestion.
Windows is by far not a real-time OS. And there are several buffers
involved when doing serial communication.. The first one when watching
from the serial cable side is the UART. This one is the one that is
affected by serial handshake. A system driver acts as the interrupt
service routine ISR whenever this buffer is nearly filled or emtied and
performs some coying to or from a system buffer. LabVIEW as user mode
program uses this buffer for ist serial reading and writing. This
system buffer is often not taken into account. Its default size is
often not as much as one would expect and some few kB of data may
easily overrun it. I have learned this when performing serial highspeed
transfer with up to 13 ports simultanously.
You can use 'VISA Set I/O Buffer Size' to set this buffer after you
have configured a serial port. AFAIK one can set the buffer size of
both directions to a value of up to 32765 bytes. Yes, not 2^15, but
2^15 - 3. But do not rely on the exact number, please.  Test it on
your system.
How can this buffer overrun?
Well, WinDoze can (occasionally) take some time where nothing happens
with end user code. This may happen when awakening the hd from power
save mode or when doing some network actions. And there are a lot of
other possibel reasons. This does not affect the system driver, which
fills up the system buffer when serial transfer is in progress.
Your code may as well operate in 'bubbles' that do not allow to empty
the buffer in-time. Think of DLL code or subroutine prioritized one.
All this may be eased if not solved by setting the system buffer size
to the limit, as it increases the delay your whole system can ignore.
Just my  Euro 0.02
Greetings from Germany!<br>-- <br>Uwe