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. 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. 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: I won’t cover the details of that here but will assume that you are familiar with the device support interface. 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:.

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This document assumes that you’re writing an EPICS Device Support layer for a moderately complicated instrument or epicw that interfaces through an RS or similar serial port, and hence you need to use the asynOctet generic serial interface.

How To Write Device Support that uses Asyn Driver – EPICSWIKI

Retrieved from ” https: Finally don’t bother checking the pau value returned by the above method for a NULL value. 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. 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.

This page was last edited on 19 Aprilat The first part is required to support the latter, so I’ll talk about the two together. 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: 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.

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Spread around the source file and in the initialization routine, we’ll have bits of code like these:. 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.

How To Write Device Support that uses Asyn Driver

The asynDriver Documentation describes the fields inside the asynDriver structure. Next note that we’re passing in two parameters to the call, myCallback and myTimeout. Epiics 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. In asn 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.

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

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:. First, you will need to write the code for a basic device support layer. 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.

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Some of these fields we are allowed or even expected to set, whereas others should not be touched. I won’t cover the details of that here but will assume that you are familiar with the device support interface.

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 function pointer found in the global pasynManager structure.

The fields we’ll be using are:. Writing software that calls Asyn is confusing until you understand the approach it expects you to use. This page Page Discussion History.

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. If the device you’re controlling is dpics 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.

You must use the methods provided by asynManager. There are very good reasons behind the design of Asyn which is intended to simplify the elics involved in writing robust, portable code, but this does result in the need to learn the Asyn approach.

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 ssyn hold other information related to your connection.