Experimental Physics and
Industrial Control System

"Mark Rivers" <[email protected]> · Thu, 15 Jul 2010 18:31:05 -0500

That would be a workaround, and might solve this problem.  But I think
there is a design problem in devGpib that should also be fixed.

Mark

-----Original Message-----
From: Maren Purves [mailto:[email protected]] 
Sent: Thursday, July 15, 2010 6:26 PM
To: Mark Rivers
Cc: [email protected]; [email protected]
Subject: Re: devGpib problem

Can you set the timeout to something long enough to always
catch the response?
(we occasionally do things like that on serial lines)

Maren

Mark Rivers wrote:
> One more point: once a timeout occurs the device is hopelessly
confused
> from that point on, because devGpib is always reading stale responses
> from the driver, not the response to the current query.
> 
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Mark Rivers
> Sent: Thursday, July 15, 2010 6:18 PM
> To: [email protected]; [email protected]
> Subject: devGpib problem
> 
> Folks,
> 
> I was helping Shifu Xu from APS debug a problem talking to a power
> supply using devGpib today, and I think I've found a problem with
> devGpib.  I have never used devGpib myself, so I could be mistaken.
> 
> Shifu's device is a TCP/IP power supply, talking a simple ASCII
> protocol.  When talking to the device it usually responds quickly, but
> occasionally the responses are very delayed.  Whether this is due to
the
> device or to the APS network is not clear, but in any event sometimes
> the response does not occur until after the 2 second timeout specified
> in the devGpib file.  However, the device does appear to always
> eventually reply.
> 
> The records in question are input records (volts, current, status,
etc.)
> that are periodically processing, and each sends a query and reads the
> response.
> 
> The problem occurs when there is a timeout.  The device does
eventually
> send the requested response.  This stale response is read by the TCP
> driver.  The devGpib driver does not appear to do a "flush" before it
> does its atomic write/read operation.  Because it does not do a flush,
> it does a write, but then when it does a read it does not get the new
> data from the device, but rather it gets the stale response to a
> previous command.  Because it is getting stale data, it is not even
> necessarily the response to the correct command, so volts are getting
> read as current, etc.
> 
> It would seem to me that this is really a bug in devGpib, and it
should
> always flush any stale data from the port driver before it does the
> write/read operation.
> 
> Is there anyone more familiar than I with devGpib who can comment on
> this?
> 
> Who is taking ownership for devGpib?  It is part of asyn, for which I
am
> nominally the contact person, but I really don't want to maintain
> devGpib.
> 
> Eric?
> 
> Thanks,
> Mark
> 
> 
> 

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System