Experimental Physics and
Industrial Control System

<[email protected]> · Wed, 30 Sep 2009 17:39:12 +0100

(Another thing to hate about Outlook: I meant to CC everybody, so this is a resend.)

From: Shen, Guobao [mailto:[email protected]] 
> But I do not understand why you want to implement TIME and 
> CTRL separately.
> The TIME returns IOC time stamp, and CTRL return value, 
> status, severity, and so on.
> It means we have to get time stamp using
>      caget(pv_name, datatype, format=FORMAT_TIME).stamp,
> and get its value, status, and severity using another channel access
>      caget(pv_name, datatype, 
> format=FORMAT_CTRL).value/status/severity
> 
> The value might be changed when we do second channel access.

Well, this is entirely down to what channel access provides.  The channel access DBR_CTRL_ (or DBR_GR_) formats don't deliver timestamps, that's fixed in channel access.  If you want timestamps you have to use a DBR_TIME_ format, there's no choice.  All cothread does is package these options in a pretty way: you always get all the information that channel access delivers.

In fact, doing a camonitor on a CTRL format is going to be frustrating: my experience is that most servers send the full data (units, precision, etc) on the first update ... and then send blanks or zeros thereafter.  But this is all down to the whim of channel access and the server.

However, you've missed one thing: when you ask for FORMAT_TIME, you also get status and severity at the same time.  You only use FORMAT_CTRL if you want to read the units/enums/precision/whatever.
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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System