[Halld-online] Asynchronous scaler readout in Hall D

[boiarino at jlab.org]

In CLAS12 all JLAB discriminators will be located in ROCs,
they are combined with corresponding TDCs
in the same crates (2 v1190s and 16 discr, or 6 v1290s and 12 discr).
It makes wiring and maintenance more convenient, and scalers -
available for both DAQ and EPICS for direct readout.
Sergey

> To all concerned with scalers in the Hall D Online,
>
> Hovanes, Dave and I met to consider many details of dealing with
> scalers. We propose the guidelines below. Note that these refer to
> normal data taking, not to code development/debugging efforts.  Further,
> the discussion below refers to asynchronous readout of scalers, not to
> how scalers are read out and inserted into the data stream.
>
>
> - the preferred method for reading scalers asynchronously (i.e. from
> registers) is to use a single process that writes to shared memory.
> This allows us to control resource usage on the ROC's and manage ROC
> processes.
>
> - this process is independent of the DAQ system. It should be the only
> processes that reads scalers from the registers, even the ROC code
> should not do this.
>
> - any other process that needs scaler data can get it from the shared
> memory. This includes an EPICS IOC process and perhaps other processes.
>
> - current thinking is to use an EPICS IOC to serve asynchronous scalers
> out to monitoring processes or to servers that bundle and then
> redistribute scaler and other data.
>
> - One question that arose was whether all crates should be part of the
> DAQ system. In particular, should the discriminator crates include a TI
> board, accept triggers, be part of the CODA DAQ configuration, etc?  In
> favor is the simplicity of putting discriminator scalers in the data
> stream and the fact that in this way it is possible to read scalers out
> of all crates at the same time.  The downside is that more crates will
> have to participate in the DAQ system and that there are other ways to
> get discriminator scalers into the data stream.
>
>
> Comments, questions, concerns...?
>
> Thanks,
>
> --
>
> 				Sincerely,
> 					Elliott
>
>
> ================================================================================
>
>
>   Those raised in a morally relative or neutral environment will hold
> 		    no truths to be self-evident.
>
>
> Elliott Wolin
> Staff Physicist, Jefferson Lab
> 12000 Jefferson Ave
> Suite 8 MS 12A1
> Newport News, VA 23606
> 757-269-7365
>
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