Experimental Physics and
Industrial Control System

Carl Lionberger <[email protected]> · Tue, 04 Sep 2007 16:49:10 -0700

Although the concept of directly calling API functions from EPICS sounds
very clean I know of no way of handling the parameterization properly.
Two approaches I might use are:
1. Use subroutine (ie, "sub") or genSub records. In this case you
would have to write a C function that maps the API function parameters
into the subroutine record parameter fields and reads or writes those
fields as appropriate when the record processes. This way you could
still reasonably approximate the API functional layout.
2. Write custom device supports for whatever record types seem
appropriate, using the API at the next level down, corresponding to
driver support. In the case of complex devices this leads to a suite of
device supports. In the case of an oscilloscope, I would use ao records
for many of the controls, waveform records for reading the traces, mbbo
for selecting triggering modes, and so forth. This method can achieve a
high level of integration between device and EPICS functionalities.
Carl
Gabriel L. Rael wrote:
Hello, all.
We are in the process of creating an EPICS interface to our
oscilloscope. It is a PCI device with its own kernel driver and user
space driver with the host processor that will be running our EPICS IOC.
It seems that though EPICS supports a list of communication interfaces
(GPIB, VME, VXI, serial, etc.), it does not allow for a device to be
connected above this layer through an ANSI-C API easily. Though asyn
device support is a complete solution down to the kernel level, we
want to be able to leverage our existing drivers.
For packaging up this functionality, we want to create records that
map directly to our API calls, which are functions with variable
arguments, some that may be passed by reference for modification. We
have function tables containing our calls with variable argument
types, but we are not seeing a common way to link PVs to function
calls with arguments. In the dbd, we are doing something like:
device(ao, INST_IO, devScopeao, "scopeAPI"). Can I use the INP and
OUT fields arbitrarily, parsing a common syntax (i.e. a single string
value such as "@function arg1 arg2") in the device support layer, to
make function wrappers? Is there a general way that we can hook into
something that already accomplishes this? Does this break the ability
to link PVs properly? Can I do this using the standard record types?
Am I missing something else?
Thanks in advance!
-glr

--

Carl Lionberger
510 486 7503

Software Developer, Engineering Division

Lawrence Berkeley National Laboratory

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System