Re: Normative types (again...)

[Ralph Lange <ralph.lange@gmx.de>]

Here's - for reference - what OPC UA defines. Pretty close to CA. Using precision on time values is interesting and makes sense.

ValuePrecision can be used for the following DataTypes:

For Float and Double values it specifies the number of digits after the decimal place.

For DateTime values it indicates the minimum time difference in nanoseconds. For example, a ValuePrecision of 20 000 000 defines a precision of 20 ms.

The ValuePrecision Property is an approximation that is intended to provide guidance to a Client. A Server is expected to silently round any value with more precision that it supports. This implies that a Client may encounter cases where the value read back from a Server differs from the value that it wrote to the Server. This difference shall be no more than the difference suggested by this Property.

On Fri, Apr 13, 2018 at 6:15 PM, Andrew Johnson <anj@aps.anl.gov> wrote:

Hello Kay,

On 04/13/2018 10:57 AM, Kasemir, Kay wrote:
> From: Michael Davidsaver <mdavidsaver@gmail.com>
>> ..  QSRV .. couldn't quite bring myself to publish printf-like specifiers over the network.
> I understand.
>
>> QSRV ..  Use  var("qsrvDisableFormat", "0") to enable display.format
> OK, Timo, try that.
>
> Is this a topic for the upcoming developer's meeting at BNL?

I just added it to our collection of topics to discuss then (a Google
doc linked from Tuesday's Core meeting minutes).

> The idea behind sending the printf format is that the client doesn't need to do anything but call printf.
> That doesn't work for clients which may want to use "precision from PV", but not the whole format.
>    display.precision = number of digits
>    display.type = decimal, exponential, engineering, hexadecimal, ..
> would allow sending the format hints, but then allow each client to decide which of those hints it uses.

Thanks,

- Andrew

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