I won’t cover the details of that here but will assume that you are familiar with the device support interface. Finally don’t bother checking the pau value returned by the above method for a NULL value. Some of these fields we are allowed or even expected to set, whereas others should not be touched. In fact I’m not really going to talk about device support very must at all, other than to explain how the design of Asyn intrinsically allows you to implement asynchronous device support. Since you can’t really do anything much in Asyn without an asynUser , lets start by creating one:. Writing software that calls Asyn is confusing until you understand the approach it expects you to use. Well apparently it simplifies matters for the authors of Asyn, or so they tell me, so that’s the way we have to do it.
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Next note that we’re epic in two parameters to the call, myCallback and myTimeout. If the device you’re controlling is simple you may be better off using the devGpib interface layer which also works with serial devices now that it’s been converted to use Asyn.
Some of these fields we are allowed or even expected to set, whereas others should not be touched.
Once you understand the choices that Asyn has made though, writing the software is actually simpler than it would be without asyn. If it’s available the Streams serial device layer from Dirk Zimoch may be even better, as it will be able to send and parse many typical serial message formats without your having to write any C code at all.
The first thing to notice is that we’re not calling a regular function, we’re actually making a call through a function pointer found in the global pasynManager structure. In fact I’m not really going to talk about device support very must at all, other than to explain how the design of Asyn intrinsically allows you to implement asynchronous device support. Writing software that calls Asyn is confusing until you understand the approach it expects you to use.
How To Write Device Support that uses Asyn Driver
If you’re wanting to use some other Asyn interface then the techniques discussed here should still apply, but some of the specific code will need to change. The first header is needed for all code that is going to call Asyn; the second only if you’re planning asgn using the serial handling, which we are for the purposes of this document.
Spread around the source file and in the initialization routine, we’ll have bits of code like these:. Initially you will probably create an asynUser for each record, since at least in theory the user could create a database that processes all your records at once.
The fields we’ll be using are:. The first part is required to support the latter, so I’ll talk about the two together.
Browse Main page Recent changes Random page Help. It is also possible to use Asyn to implement synchrous device support, but I’m not going to talk about that here at all. If we want to talk to a real awyn device that already has an asyn Port registered, we have to connect to it by name:. Finally don’t bother checking the pau value returned by the above method for a NULL value.
How To Write Device Support that uses Asyn Driver – EPICSWIKI
You must use the methods provided by asynManager. Since you can’t really do anything much in Asyn without an asynUserlets start by creating one:. There are very good reasons behind the design of Asyn which is intended to simplify the work involved in writing robust, portable code, but this does result in the need to learn the Asyn approach.
This page was last edited on 19 Aprilat This document assumes that you’re writing an EPICS Device Support layer for a moderately complicated instrument or device that interfaces through an RS or similar serial port, and hence you need to use the asynOctet generic serial interface. Retrieved from ” https: Assuming you’ve got your basic device support framework sorted out, there are usually only a couple of places where your code will actually need to interact with the Asyn software at all: If createAsynUser wasn’t able to allocate enough memory for the structure it won’t bother to return at all; if there’s not enough spare RAM at this stage, our IOC is never going to be able to run properly that’s the theory anyway, don’t blame me I didn’t write it This page Page Discussion History.
These are both names of functions that we have to provide and which will be called by Asyn at an appropriate time – we’ll come back to them again later.
Well apparently it simplifies matters for the authors of Asyn, or so they tell me, so that’s the way asym have to do it. I won’t cover the details of that here but will assume that you are familiar with the device support interface.
It’s worth knowing that you really can’t create, copy or destroy an asynUser object yourself, because it’s actually implemented as a part of a larger structure which the asynManager routines use to hold other information related to your connection. First, you will need to write the code for a basic device support layer.
The asynDriver Documentation describes the fields inside the asynDriver structure.