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<== Date ==> <== Thread ==>

Subject: Re: Is it possible for an Asyn output record to be, also, an (I/O Intr - driven) input?
From: Ralph Lange <[email protected]>
To: EPICS Tech-Talk <[email protected]>
Date: Fri, 28 Nov 2014 15:39:07 +0100
On 28/11/2014 14:09, [email protected] wrote:
This is possible (the motor record is a good example), but it needs the record type to support it. Most record types don’t support two way communication with device support.

When properly done in device support, it works with all standard record types, and does not need any special support from the record type. (The mentioned OPC support is a good example.)

Here's how it is basically done. It boils down to: Fake the second phase processing of an asynchronous operation.

The record processes asynchronously. (I.e. it is processed twice. First phase processing sends the request and leaves PACT true, the incoming acknowledge message from the device triggers the second phase processing.)

The device link must be set up providing definitions for a data set (command) message (from IOC to device) containing the data, and a data update message (from device to IOC) containing the data.

Device side:
When receiving a set message, the device may ignore or execute the request. It should always answer with an update message containing the result of the operation (i.e. changed or unchanged data).
When another master (local, external, whatever) changes the data, the device sends an update message containing the new data.

IOC side:
On first phase processing (PACT was false), the device support sends the set message, and sets PACT=true.
On incoming update message, the device support always sets PACT=true and triggers the second phase processing.
On second phase processing (PACT was true), the device support copies data to the record and sets PACT=false.

Simple. Effective. Works with standard record types.

Cheers,
~Ralph


Replies:
RE: Is it possible for an Asyn output record to be, also, an (I/OIntr - driven) input? Heesterman, Peter J
RE: Is it possible for an Asyn output record to be, also, an (I/O Intr - driven) input? Mark Rivers
References:
Is it possible for an Asyn output record to be, also, an (I/O Intr - driven) input? Heesterman, Peter J
RE: Is it possible for an Asyn output record to be, also, an (I/O Intr - driven) input? nick.rees

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