Experimental Physics and
Industrial Control System

Hi Emmanuel,

Depending on how much processing you need to do and how long it takes,
this should perhaps be an asynchronous device.  If you make it
synchronous, then it will block other EPICS devices while it is
processing.  If the computation takes more than a msec or so you should
make it asynchronous.

In general the advantage of asyn for synchronous devices is:

- You can use generic device support, no need to write specialized
device support.

- Your driver architecture will work when you port to a device that is
asynchronous (or decide later it should be asynchronous).

- You have well-defined interfaces between device support and your
driver.  The alternative is to create your own interfaces, with
associated debuging.

I am not sure what you mean the "the upper asyn layer does all of the
image processing".  Is this actually in an asyn port driver?

Mark


> -----Original Message-----
> From: [email protected] 
> [mailto:[email protected]] On Behalf Of Emmanuel Mayssat
> Sent: Monday, September 10, 2007 2:13 PM
> To: [email protected]
> Subject: asyn for synchronous devices
> 
> Hello
> 
> It is said that asyn can be used for synchronous devices.
> I am contemplating using asyn for my video acquisition driver.
> Is that a good idea? As anybody done this?
> 
> The design could be as follow:
> If I use a PCI frame grabber I instantiate the PCI interface.
> If I use a streaming server (AXIS), I instantiate the axis network
> interface.
> If I want a set of test images, I instantiate a dummy interface, etc.
>  
> The upper asyn layer does all the image processing (such as profile
> calculation, etc). The interface is actually the "hardware driver" and
> its purpose is only the acquisition of a snapshot (in a 
> specific format)
> and the generation of software interrupts.
> 
> Is this a good design for asyn sync drivers?
> Should the profile calculation be part of the interface and the
> interrupt be generated when all the processing has been completed?
> 
> How can I justify using the asyn driver for sync devices over other
> methods? what are the benefits of using asyn here?
> 
> --
> Emmanuel
> 
> 
> 
> 

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