EPICS ASYN DRIVER

The first part is required to support the latter, so I’ll talk about the two together. First, you will need to write the code for a basic device support layer. The first header is needed for all code that is going to call Asyn; the second only if you’re planning on using the serial handling, which we are for the purposes of this document. You must use the methods provided by asynManager. Browse Main page Recent changes Random page Help. 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: 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.

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The first part is required to support the latter, so I’ll talk about the two together.

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.

I won’t cover the details of that here but will assume that you are familiar with the device support interface. 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 Well apparently it simplifies matters for the authors of Asyn, or so they tell me, so that’s the way asyb have to do it.

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. This page Page Discussion History.

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Some of these fields we are allowed ssyn even expected to set, whereas others should not be touched. It is also possible to use Asyn to implement synchrous device support, but I’m not going to talk about that here at all.

How To Write Device Support that uses Asyn Driver

This page was last edited on 19 Aprilat Retrieved from ” https: The asynDriver Documentation describes the fields inside the asynDriver structure. It’s eepics 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.

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 epicd C code at all. 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 epixs the need to learn the Asyn approach.

The fields we’ll be using are:. Since you can’t really do anything much in Asyn without an asynUserlets start by creating one:. The first thing to notice is that we’re not calling a regular function, we’re actually making a call through a epcs pointer found in the global pasynManager structure.

First, you will need to write the code for a basic device support layer. Next note that we’re passing in two parameters to the call, myCallback and myTimeout.

How To Write Device Support that uses Asyn Driver – EPICSWIKI

Asn first header is needed for all code that is going to call Asyn; xsyn second only if you’re planning on using the serial handling, which we are for the purposes of this document.

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Spread around the source file and in the initialization routine, we’ll have bits of code like these:. You must use the methods provided by asynManager. If we want to talk to a real world device that already has an asyn Port registered, we have to connect to it by name:.

If epis 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.

Writing software that calls Asyn is confusing until you understand the approach it expects you to use. Browse Main page Recent changes Random page Help. Finally don’t bother checking the pau value returned by the above method for a NULL value.

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. 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. 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: 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.

Once you understand the choices that Asyn has made though, writing the software is actually simpler than it would be without asyn.