[Halld-tracking-hw] F125ADC what do we want / need

[Naomi Jarvis]

Hello,

I prefer option 1, the coupled words with pedestal, as it packs more info into the same space.

First word

Do we need the 2bits for 'pulse'?  From looking through the spec it seems that this is to label up to 4 pulses for which time data is to be sent.  For the CDC this would always be 1, just 1 pulse, so could we dispense with it?

We would like to increase the bits available for time data from 10 to 11 bits, as an integer # of ns, that gives us 0-2047 ns.  This allows some headroom for slower drift times. 


Second word

Pedestal.  I would indeed like to include this but it is not necessary to have full range 0-4095 available in integer steps.  We will set the pedestals to something low, ~55-60.   How about outputting pedestal/8 to cover the subrange pedestal=0-504 as pedestal/8=0-63 in 6 bits.  ?   

Integral.  OK.

Integral quality factor.
I would like to include a count of the number of overflowed samples contributing to the integral, this could count up to 63 samples (504ns) in the 6 bits freed up from the pedestal.  

How does this sound?

Naomi.


On Jul 8, 2013, at 11:31 AM, David Lawrence wrote:

> 
> Hi All,
> 
>   I spoke with Beni a little about this this morning since I am currently
> working on the code that parses this for the online monitoring and
> the offline. I have not been involved in any other discussions, but here
> are some thoughts based on what I've seen in the F250ADC formats
> and my discussion with Beni:
> 
> 1.) It is not possible to fit both the sum and the pulse time into a single
> 32-bit word. The word must have at least 12 bits of info to define the
> data type and channel number leaving only 20 bits for payload. Hits
> in the F125 must therefore span two 32-bit words.
> 
> 2.) The FADC250 has a specification where the pulse time and pulse
> integrals appear as separate data types (i.e. they appear in separate
> 32-bit words). This allows the option of having a module output one
> of these but not the other. In practice, we will probably never want to
> do this, but thee spec. allows it. To see the spec, look here, but
> be aware a few things in the headers have changed:
> 
> https://halldweb1.jlab.org/wiki/images/d/db/FADC_Data_Format_V2.pdf
> 
> 
> 3.) For the FADC125, we could decide to couple the two words and
> eliminate redundant information such as the channel number,
> pulse number, and slot. This frees up enough bits to record a 12bit
> pedestal with every hit. I've drawn this out in the diagram below
> labeled Option1: to show how we could pack the bits in a format
> consistent with the spirit of the current F250 spec.
> 
> 4.) We could also follow almost exactly the format of the F250 spec.
> with the difference being that we need 7bits instead of 5 for the
> channel number in the F125. I've drawn this up as Option 2:
> below.
> 
> 5.) We could also have something completely different from either
> of these. In any case, we'll want the block header/trailer and
> event header words to follow the standard format for JLab modules
> whose current specification is here:
> 
> https://halldweb1.jlab.org/wiki/images/5/58/JlabModuleDataFormat.pdf
> 
>  
> <fffahdgj.png>
> <bgahdiae.png>
> Regards,
> -David
> 
> On 7/8/13 9:17 AM, Beni Zihlmann wrote:
>> Hi All,
>> we have to come up with a list of specifications of the data we
>> want to have from the ADC. I would like to use this email to
>> initiate a discussion and put this topic on the agenda of the
>> next tracking meeting. By that time we should have a clear
>> understanding of what is needed so that the experts Cody
>> and Gerard can tell us what is feasible and what not.
>> 
>> cheers,
>> Beni
>> _______________________________________________
>> Halld-tracking-hw mailing list
>> Halld-tracking-hw at jlab.org
>> https://mailman.jlab.org/mailman/listinfo/halld-tracking-hw
> 
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