GPIB Controller and Asynchronous Programming

[FefeOxy]

Hi,

I've been trying to write a large software that will allow me to
automate various GPIB programs all at once. I'm new with GPIB commands
so I need to ask this question: what happens if the program sends out 2
GPIB commands at the same time? or when the other command is not ready
to be sent? I'm trying to decide if I need to have a static "wait"
member that will block any write/query command on the GPIB bus until
the line is free. And if so, what commands do I use to figure out if
the line is busy or not? *OPC?

Thanks you.

[Makoto]

I believe you are trying to send GPIB commands at the same time from multiple threads or processes.  Normally GPIB and/or VISA driver does process its own mutual exclusion, keeping all the write/read function calls to be serialized.  Therefore multiple GPIB commands are never be cross-overlapped. 

Other case is that one thread (or process) sends a GPIB command and then reads the response, at the same other thread sends a different GPIB command then reads the response.  For example, the thread #1 is querying "*IDN?" and the thread #2 is querying "MEAS:VOLT?".  In this case, you should use Lock/Unlock functions to avoid the two query pairs from cross-overlapping.  If overlapping, sending "MEAS:VOLT?" command immediately after the "*IDN?" command without reading response will corrupt the IDN response to receive.

The Win32 functions for lock/unlock are Semaphoe, Critical-Section, or Mutex.  the VISA library also provides this kind mechanism for multiple VISA sessions that access the same I/O resource at the same time.