Experimental Physics and
Industrial Control System

Tim Mooney <[email protected]> · Fri, 13 Jul 2007 12:39:20 -0500

Stefan Heim wrote:

Hello all,
I have a device that came with a controller from the vendor. This controller
offers a TCP/IP server you can connect to and send a certain set of commands
to operate the device.
Using EPICS, asyn and streamdevice, it has been close to trivial to set up a
basic softIOC to operate the device (essentially a getPosition/setPosition
operation).
In the streamdevice protocol file I have (among others)
getX {
        out "Joe Crds ?";
        in "Joe Crds %f %*f %*f %*f %*f %*f %*f ";
}
setX {
        out "Joe AxisAbs 1 %(VAL)f";
        in "Joe started";
}
In the database I have (among others)
record (ai, "MyIOC:X")
{
        field (SCAN, ".1 second")
        field (DTYP, "stream")
        field (INP,  "@device.proto getX MYPORT")
	# EGU, HOPR, LOPR, PREC, warning limits, ... left out for brevity
}
record (ao, "MyIOC:setX")
{
        field (SCAN, "Passive")
        field (DTYP, "stream")
        field (INP,  "@device.proto setX MYPORT")
	# EGU, DRVL, DRVH, PREC, warning limits, ... left out for brevity
}
This works like a charm, I can do "caget MyIOC:X" to get the current position
and "caput MyIOC:setX <targetpos>" to drive to a target position.
Now I want these records to operate in different, linearly transformed
coordinates rather than in the device's very own coordinates, let's say for
example
myCoords = -20.5 * devCoords + 5.3 .
Therefore, I added
        field (ASLO, "-20.5")
        field (AOFF, "5.3")
to the ai and ao records described above; for the ai record, this had the
desired effect, i.e. the record now delivers the position in transformed
coordinates.
However, the ao record _ignores_ ASLO and AOFF with a streamdevice device
support. Is this the intended behaviour? Or a bug in streamdevice's device
support for the ao record?

I think you are *telling* the streamDevice to ignore ASLO and AOFF, by
using the

format "%(VAL)f". As I read the doc, it would do what you want if you
used the

format "%f". According to streamDevice/doc/ao.html, the streamDevice would,

in this case, perform the calculation

|OUTPUT_VALUE = (OVAL-AOFF)/ASLO

without converting to integer. (I.e., the streamDevice would grab the
required

field values, and perform the calculation independently of the record.)

|

How are you supposed to solve the problem of linear coordinate transformations
without adding a bunch of helper records (calc & calcout, or even motor) to
the database? 
The LINR="Slope" ESLO/EOFF scaling of the ao record would be sufficient, if
only RVAL was a double rather than a long; atm if you use it, it
truncates "devices coordinates" to whole numbers after doing the correct
transformation.
Any suggestions?
-Stefan

Tim Mooney

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System