[Halld-online] Asynchronous scaler readout in Hall D

[Elliott Wolin]

Hi Vardan,

Thanks, I was considering this, but need to learn more about Afecs 
components.  Note that the shared memory has to be accessible by C programs.



On 02/07/2012 01:46 PM, Vardan Gyurjyan wrote:
> 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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-- 

				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

================================================================================