Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Fri, 11 Dec 2015 15:28:44 -0600

Hi Rolf,

On 12/11/2015 01:55 PM, Rolf Keitel wrote:
> I have an IOC with an analog input record on a fixed scan time, say .5
> seconds, with the INP link targeting the value of an analog record xxx
> in a second IOC.
> What does the first IOC do? Does the CA client in the first IOC
> subscribe to a monitor from xxx and updates the first record twice a
> second? Or does the first IOC issue a synchronous CA get twice a second?

The dbCa link code sets up a CA monitor the first time it is asked for a
value (until that first request it doesn't know what data type the
record wants, so it can't create the monitor at link connection time).
The monitor callback caches the latest value in a buffer associated with
the link. When the record subsequently asks for a value from the link,
it is immediately given the value from its cache.

Link operations have to return immediately, they can't block while they
wait for I/O to take place, so issuing ca_get() requests wouldn't be
possible.

HTH,

- Andrew

-- 
Light thinks it travels faster than anything but it is wrong.
No matter how fast light travels, it finds the darkness has
always got there first, and is waiting for it.
    -- Terry Pratchett, Reaper Man

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System