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Re-4: vrf VRF error in direct I/O

Question asked by tw on Nov 23, 2005
can you show me a example how you suggest to delete the input buffer from a direct I/O ??
So that I can be shure that old parts from a wrong communication are deleted.
Thomas


-------- Original Message --------
Subject: RE: Re-2: [vrf] [VRF] error in direct I/O (24-Nov-2005 14:51)
From:    shawn@testech-ltd.com
To:      tw@huber-online.com

> > is there a protection in hpvee that
> > they do not write and read at the
> > same time.
>
> Yes and no. It's impossible for two different "threads" to write to the
> same
> port at the same time because they're not really executing in parallel,
> HOWEVER, the quantum of VEE IO is the transaction object. If you query an
> instrument for its output buffer size and then set up a loop to read the
> buffer, it is entirely possible that another thread can preempt the loop
> outside of a transaction object and mess you up.
>
> One way around this is to define *different* instruments that point to the
> *same* port. I guess probably VEE opens different session handles for the
> different instruments and the synchronization is implicit in the SICL
> library. I've used this method for four different threads all talking to 96
> different instruments and it works famously. There are four "virtual"
> instruments that each cycle through 96 different addresses. I tried many
> different ways to synchronize IO, and this was the only one that worked.
>
> Another way is to contain all transactions that must not be preempted in a
> thread which won't be preempted. One of the conditions under which VEE won'
> t
> preempt a thread is a function call made from a Formula Object that's fed
> with a Formula control input. Another is an ActiveX event. I haven't used
> these.
>
> > After that I send a new question
> > to the partner and when he answer,
> > is there than a problem at the
> > buffer input from the direct I/O ?
>
> Most definitely. If I remember correctly, that's -410, stale data.
> -SHAWN-
>
>
>
> To: tw@huber-online.com
>     vrf@agilent.com


To: shawn@testech-ltd.com
Cc: vrf@agilent.com


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