Re: EPICS V3 PV name length limits and how to get around them

[Ralph Lange via Core-talk <core-talk@aps.anl.gov>]

On Thu, 22 Nov 2018 at 16:13, Benjamin Franksen via Core-talk <core-talk@aps.anl.gov> wrote:

Am 19.11.18 um 18:29 schrieb Johnson, Andrew N. via Core-talk:
> The CA protocol's channel name length is not limited by the size of the
> NAME field in the IOC.

I am aware of that. Sorry for not expressing myself clearly.

> Ben, what limitations are you trying to solve, and how do you know that
> they actually exist?

Basically, the limit of 40 bytes on the DBR_STRING data type. Which in
turn implies a limit on the length of things you can put into link
field.

I don't quite understand.

Link fields have much wider limits: pushed to 128 then 256 chars in 3.15; unlimited in 7.0

Setting those fields through CA is possible using the "long string" mode, i.e. by writing an array of char to the PV which gets a "$" suffix.

ralph@debian-testing:~$ caput -S ai.INP$ this_is_an_extremely_long_string_that_still_can_be_written

Old : ai.INP$ 

New : ai.INP$ this_is_an_extremely_long_string_that_still_can_be_written NPP NMS

So: which use case is not solved by the currently available mechanisms?

Cheers,
~Ralph