Sphenix-tpc-l mailing list

[Takao Sakaguchi <takao AT bnl.gov>]

Hi Martin,

 The brief answer is that SAMPA itself can delay its
data output by 192 samples in terms of ADC clocks
at maximum (it is programmable up to 192).

 This means effectively, ~90 beam crossings since we
will likely operate at 20MHz ADC clock. I would expect
that we also have delays in the FPGA by a few ticks
(I think this is programmable in some way).

 By the way, we may want to see the pre-trigger data

somewhat, so I think 80 ticks is a safe answer for TPC.

Takao

On Fri, Oct 20, 2017 at 1:09 PM, Martin Purschke <purschke AT bnl.gov> wrote:

To the TPC aficionados -

I'm in the process of compiling the "trigger latency map", usually
expressed as the number of beam crossings we can let go by before we
need a trigger decision. For example, the INTT allows for 70 ticks (data
from 64 crossings stored, plus 6 crossings before the data from a given
crossing reaches the FEM).

I'm aware that a number of assumptions will have to be made for the
answer, especially the assumption that we will be able to correlate the
streaming data with triggered events. This is both a matter of technical
feasibility and of the "waveform overlap fraction" for close-by events,
namely, can we afford the duplication of waveform snippets where they
overlap in time?  We believe that the answer to the former is a
tentative "yes" and to the second a "most likely". I recall a 6% data
duplication figure but might not remember it correctly.

JohnK and I started to discuss this and the assorted strategies. I would
ask you guys to toss that around some in the larger group so everyone is
on the same page. If you come up with an answer that is guaranteed to be
larger than about 70 ticks, you will not be constraint and can stop
calculating it more accurately.

Preferably I would like the answer before the end of next week, as we
want to get going polishing the CDR and this is the key number the LL1
triggers need.

        Thanks a bunch,

                Martin

--
Martin L. Purschke, Ph.D.        ;   purschke AT bnl.gov
                                 ;   http://www.phenix.bnl.gov/~purschke
                                 ;
Brookhaven National Laboratory   ;   phone: +1-631-344-5244
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Upton, NY 11973-5000             ;   skype: mpurschke
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--

Takao Sakaguchi
Brookhaven National Laboratory
Physics Department, Bldg. 510C
takao AT bnl.gov
Office: 1-631-344-3345