Experimental Physics and
Industrial Control System

Stefan Heim <[email protected]> · Fri, 31 Aug 2007 02:54:44 +0200

Hi,

sorry for the following lengthy expose to a problem regarding completion 
notification.

I have several positioners (multiple axes devices) controlled via several 
get/set pairs of ai/ao records per axis with a StreamDevice device support 
(DTYP=streams).

Sometimes, the underlying "hardware" protocol offers only a set method without 
completion notification for a given axis. The StreamDevice protocol file 
section then has s.th. like

> setX {
>         out "AxisAbs 1 %f";
>         in "AxisAbs 1 movement_started";
> }

Here the device emits the "AxisAbs 1 movement_started" as mere confirmation of 
the control order. There is no further reply indicating completion of the 
positioning operation. 

While moving, the position can be monitored in an event based manner, i.e. 
a .SCAN="I/O Intr" ai record

| record (ai, "$(IOCNAME):stage:$(AXIS)")
| {
|         field (SCAN, "I/O Intr")
|         field (DTYP, "stream")
|         field (INP,  "@protocol_file.proto get$(AXIS) PORT")
| }

based on a protocol

> getX {
>         @init {
>                 out "registerVC 2 IOC:stage:X Joe";
>                 in "Joe Crds %f %*f %*f %*f %*f %*f %*f ";
>         }
>         in "Joe Crds %f %*f %*f %*f %*f %*f %*f ";
> }

Here, the device's capability to do registration based position monitoring is 
gluelessly linked with EPICS' monitor concept. The out command issued during 
init causes the device to send position update messages ("Joe Crds ...") as 
if you posted a monitor on one (or several) EPICS process variable(s).

The six floats thrown away in the "in" part of this protocol ("%*f") are 
typically read by a further set of (six) .SCAN="I/O Intr" ai records, 
offering completely seperated control information and linear rescaling of the 
raw values by means of the respective .ASLO and .AOFF fields. With the 
same .ASLo/.AOFF rescaling applied to the corresponding ao record of a given 
axis, this rescaling is transparent to the user/client.

In addition, there is a state variable ("ready") available with the same 
subscription based event notification mechanism,

| record (bi, "$(IOCNAME):stage:ready")
| {
|         field (SCAN, "I/O Intr")
|         field (DTYP, "stream")
|         field (INP,  "@protocol_file.proto getReady PORT")
|         field (ZNAM,  "not ready")
|         field (ONAM,  "ready")
| }

with protocol 

> getReady {
>         @init {
>                 out "registerVC 32 IOC:stage:ready Joe";
>                 in "Joe %{not ready|ready}";
>         }
>         in "Joe %{not ready|ready}";
> }

Now if I want to use the sscan record to operate on these positioners, it 
expects them to do be capable of ca_put_callback()-based completion 
notification. However, e.g. travelling from 0.0 to 10.0 takes ~13 s 

| sheim@txm1:~$ camonitor TXM1CL:micos:ready TXM1CL:micos:ZCOARSE &
| [1] 7781
! TXM1CL:micos:ready             2007-08-31 02:09:33.733498 ready
! TXM1CL:micos:ZCOARSE           2007-08-31 02:09:11.154559 0 LOLO MAJOR
| sheim@txm1:~$ caput -c TXM1CL:micos:setZCOARSE 10
| Old : TXM1CL:micos:setZCOARSE        0
! TXM1CL:micos:ZCOARSE           2007-08-31 02:09:44.735909 0.022526
! TXM1CL:micos:ZCOARSE           2007-08-31 02:09:44.757608 0.039484
! TXM1CL:micos:ZCOARSE           2007-08-31 02:09:44.779335 0.061448
! TXM1CL:micos:ready             2007-08-31 02:09:44.800247 not ready
! TXM1CL:micos:ZCOARSE           2007-08-31 02:09:44.803464 0.087914
! TXM1CL:micos:ZCOARSE           2007-08-31 02:09:44.828070 0.120282
| New : TXM1CL:micos:setZCOARSE        10
! TXM1CL:micos:ZCOARSE           2007-08-31 02:09:44.849671 0.164518
| sheim@txm1:~$
! TXM1CL:micos:ZCOARSE           2007-08-31 02:09:44.870746 0.205295 
! TXM1CL:micos:ZCOARSE           2007-08-31 02:09:44.891945 0.251714
! TXM1CL:micos:ZCOARSE           2007-08-31 02:09:44.914267 0.303483
! TXM1CL:micos:ZCOARSE           2007-08-31 02:09:44.935013 0.36009
| [...]
! TXM1CL:micos:ZCOARSE           2007-08-31 02:09:45.658592 4.99687
! TXM1CL:micos:ZCOARSE           2007-08-31 02:09:45.680585 5.21379
! TXM1CL:micos:ZCOARSE           2007-08-31 02:09:45.703397 5.42912
| [...]
! TXM1CL:micos:ZCOARSE           2007-08-31 02:09:46.587214 9.98588
! TXM1CL:micos:ZCOARSE           2007-08-31 02:09:46.609446 9.99538
! TXM1CL:micos:ZCOARSE           2007-08-31 02:09:46.631317 9.99971
! TXM1CL:micos:ZCOARSE           2007-08-31 02:09:46.653736 10
! TXM1CL:micos:ready             2007-08-31 02:09:47.107716 ready

but the caput -c above returns "immediately". Furtermore, the device is 
possibly late to give out the "not ready" notification (cf. trace above), but 
guarantees to fire "ready" only after (all) movements finished. 

While I read the slides on completion notification in Scans.ppt and tried to 
understand the busy record, I still wonder what might be the best approach to 
the problem. Essentially, I need a way to use StreamDevice based devices not 
offering a synchronous setPosition command as positioners with the sscan 
record.

Any clues?
-Stefan

-- 
Stefan Heim, PhD Student X-ray microscopy
BESSY mbH, Albert-Einstein-Straße 15, D-12489 Berlin, Germany
voice: +49 30 6392 3177 fax: + 49 30 6392 4757 e-mail: [email protected]
BESSY mbH - Mitglied der Leibniz Gemeinschaft
Vorsitzender des Aufsichtsrates: Prof. Dr. Dr. h.c. mult. Joachim Treusch
Geschäftsführer: Prof. Dr. Dr. h.c. Wolfgang Eberhardt, Prof. Dr. Eberhard 
Jaeschke 
Sitz Berlin, AG Charlottenburg, HRB 14635

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System