[Halld-online] Asynchronous scaler readout in Hall D

[Vardan Gyurjyan]

Hi,
I will suggest making this process an Afecs component, that can be included into the Hall-D experiment control system. Being an Afecs component one can subscribe scaler information event not being part of the data production system ( for e.g. web or cellphone apps).
Regards,
vardan
On Feb 7, 2012, at 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,
> 
> -- 
> 
> 				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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