[Halld-tracking-hw] CDC pedestal readout needs

[Beni Zihlmann]

Hi Naomi,

1) A.) can be accommodated by raw event readout. Anything that has to do 
with determining the  proper parameters can/should be done with raw
     event data and special runs.

2) C.) is happening all the time because we get pedestal information 
with the ADC integral information (first data word). if a channel is 
never above
     threshold we never get a signal and never any pedestal information 
as you correctly state but that is as good as bad pedestal information. 
It tells us
     we have a missing channel, so we catch the problem and can check on 
it (your last point). The oline  monitoring program and shift crew 
should catch that.

3) I currently see no need to have more than two modes of readout/formats.
     a) raw readout that handles any initial determination of setup 
parameters and possible routine checks on these parameters every 
day/half-day or your most
         favourite time scale.
     b) the format we defined with 2 32bit data words. Where we have all 
the necessary information to check if the channels are healthy and we 
even can
         correct the ADC integration values if the initial pedestal is 
off because a previous event distorted it. All this is done offline 
anyway and does not
         need to be done on the FPGA.

I am currently writing down a short explanation on a first attempt of an 
algorithm that satisfies both CDC and FDC detectors in the hopes that this
algorithm can be improved on and at the same time is independent of 
whether it is used for the FDC or CDC and of course fits onto the FPGA in
the first place.


cheers,
Beni


> Hi all,
>
> The last email stream on pedestals etc made me a little dizzy.  Here I've tried to get all the CDC's pedestal measurement needs onto one page, to be sure that they are possible with the planned data formats.   I would guess the FDC would have broadly similar needs.   ?
>
>
> A. Initial setting
>
> Several samples with full range 0-4095 of adc value in order to set the pedestal offsets - I collect a number (10-100) of pedestal samples from 50-100 events and take the mean value.  There are several ways to do this (look at less samples, calculate the mean in the flash etc) but it will be easiest with full range readout available.  Also we need to measure the pedestal width which will be needed in order to set the hit thresholds in the flash.
>
> B. Event data
>
> I need some measure of the pedestal before the hit in order to determine whether it is still high from a previous hit and what is the difference between pedestal and overflow.
>
> C. Routine pedestal monitoring
>
> Pedestals need to be monitored so that any drifts can be corrected and also to keep an eye on the width (important for hit thresholds).
>
> D. Routine fadc health monitoring
>
> We should take some event data with full range and full precision sample readout to check that the adcs are ok (no bits missing) and check performance of the flash algorithms.
>
>
>
> B.  This is in the pulse data format; almost certainly a subset of the full adc range.
> D.  Would be included in the combined format for pulse data followed by raw sample data as continuation words.
>
> If we have dedicated runs with a different data format & different trigger & hit-less data then A&C could use the same raw data format.  (We could also make the flash calculate a mean & width for a different pedestal format).
>
> [I thought of monitoring pedestals via the pulse data B or raw data in the combined format for D (if they start before the trigger), but we would only be reading out the channels with hits, so would not see problems if there is a channel without hits because its pedestal has plummeted.]
>
>
> Can anyone see anything that I have forgotten?
>
> Naomi.
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