[Halld-online] Asynchronous scaler readout in Hall D

[Elton Smith]

Hi Elliott,

Maybe I'm missing something, but it seems strange that you would  
consider not having the scaler modules (i.e. discriminators) as part of 
the daq system. It would seem that any simplification would result in 
additional effort in other sectors.

My two cents, Elton.


Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite #16
Newport News, VA 23606
(757) 269-7625
(757) 269-6331 fax


On 2/7/12 1:27 PM, Elliott Wolin wrote:
> 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,
>