I have been using the EPICS server and client in LV 2009 and have encountered a number of problems. Here is a summary, with ZIP file attached. Any help will be appreciated.
Booleans published
by the server can be read by the client but not written by the client.
I can't figure out how to access any of the
fields except the VAL field for any record. The documentations says they can be
accessed and they show up on the server, but I can't get the client to access
them. If I add a field to the client record and bind it to a variable I get no
value for any field except \VAL.
Arrays have
problems. I set the environment variable EPICS _CA_MAX_ARRAY_BYTES to be 65536,
and it seems that LabVIEW makes every
EPICS array that size, even when I only want a few values. In the attached
example with an array filled with 3 values, the server writes 3 to NELM, but
the client has no way of getting that. The whole 64K array comes across, with
mostly zeros. The client has no way to tell how many values are valid and how
many are not.
When trying to write
an array from client to server a similar problem is encountered. If I only
write 3 values the array never gets
transmitted back to the server. If I write all 64K bytes it gets transmitted,
but there is no way to tell the server that only the first few values matter.
This seems very inefficient. Of course I could
use a separate PV for each array to indicate how many values it contains, but
this is a pain, and the NELM field is already there for that purpose.
I have some images
that I need to transmit, and these will be large arrays, so I might have to increase
the max size to hundreds of Kbytes, but I don't want to have to send hundreds
of thousands of zeros every time I send a 4-element array.
I could not write
the Int32 or U32 array from client to server, but the DBL array worked fine.
The Int32 array was telling me that the shared variable on the client had no
value, even when I wrote thousands of elements over and over. I just don’t
understand.
The updating of the data is erratic. At 10 Hz the values were not being posted
in a timely manner, resulting in delays followed by bursts while the server
catches up. This erratic updating is very annoying visually and means that you
can' t be sure that different displays are synchronized. It may be related to
having to publish so many large arrays needlessly. I have been using the SNS/Oak Ridge shared-memory interface to LabVIEW and it has itw own set of problems, but I can set the size of the arrays to be no larger than necessary and it updates reliably and regularly at 10 Hz. That tells me that the data rate is not excessive (if only the necessary data is sent withouta zillion extra zeros) and that the client is capable of handling the update rate.
