FA125 Meeting May 13, 2016

May 13, 2016 FA125 meeting

Connection

1. Instructions for Bluejeans meeting connection
2. Meeting ID: 290664653

Headline text

1. To join via a Web Browser, go to the page [1] https://bluejeans.com/290664653.

Agenda

1. Objectives
2. Current performance
3. Busy signal details
4. Testing plans

DRAFT Minutes NOT FINISHED YET read at your own risk

Participants: Naomi, Cody, David, Sergey, Beni, Lubomir

1. Objectives: David reminded us that the objectives for the runs in 2018 include a rate on the target of 5e7 photons/second and the DAQ running at 100kHz (a photon flux of 1e8 Hz was mentioned originally, but this was reduced to 5e7). The DAQ livetime was not mentioned but is assumed to be 90%.
2. Current performance: Cody's tests show the FA125 running at sustained rates (continuously, so 0% livetime) with the current parameters of

Window size = 200, WE>200, NP/NP2=4, Npeaks=1

Short mode processing time (trig to out)

0% occupancy (no hits) = 4.9uS = ~204kHz
17% occupancy (1 hit per chip) = 5.9uS = ~170kHz
100% occupancy (6 hits per chip, on all 12 chips) = 8.8uS = ~113kHz

Just algorithm = 4.68uS 

The card can buffer up to 4 triggers, so higher burst rates will be obtainable.

1. Busy signal (from Cody):
   1. Data from 4 hits can be buffered before the busy signal is asserted. If the data from the first hit is still processing, the busy signal would switch on when a 5th trigger is received. This 5th set of data would be processed, but data from 6th and later triggers would be rejected if the busy signal is still on. The busy signal is cleared when one set of data has been processed and there are 4 or fewer triggers (aka sets of hit data) in the buffer.
   2. Each fadc has its own busy signal.
   3. The busy signal is transmitted through the backplane; no extra wiring is needed.
   4. The propagation delay time is unknown at present. This is the time for the busy signal to go through the backplane to the SD cards to the TI board in the same crate and then through fibre optic to the TS crate. It is probably about 1us. Cody will measure this. The level 1 holdoff should be larger than the propagation delay.
   5. Any card in the system (ie any fadc from any detector) asserting busy will cause the TS to stop sending triggers until the busy has cleared.
   6. Holdoff times. The level 1 holdoff should be set larger than the propagation delay. It would be possible for the TS firmware to monitor the busy signal and count the number of triggers it has sent out but it does not do this at present. Only a minimum holdoff would be needed between the first 3 triggers (probably on the order of 10 to a few 100 ns, less than the propagation delay).
2. VME readout (from Sergey):
   1. The VME readout has a reasonable livetime up to 100kHz.
   2. It takes some time to get the data off the fadc board through the backplane. The amount of transfers are limited by the 4MB DMA protocol buffer size. The buffer must be emptied when it is filled and the 4MB is a consequence of the DMA protocol. It takes 170us to transfer this buffer with the blocklevel=20. The buffer size is set for 100% occupancy, blocklevel has to be no more than 40 for the CDC in order to fit a crateful of hits into the DMA buffer. Setting up the DMA transfer takes 100 us, transfer is much shorter (~50us). The DMA buffer is on the ROC. (So increasing the number of crates would increase the total buffers available).
   3. Using the busy signal should improve the livetime as the trigger holdoff can be reduced to min, not a conservative (worst case) value as at present. The current bottleneck is tagger fadcs (because of the cable length?).

1. Hit occupancy & search (Naomi):

Run data hit occupancy plots are mostly 0 or 1 per trigger, with an occasional 6 (100%), will produce some plots. An idea to improve the hit search by inspecting every other sample instead of every sample (as we require 2 consecutive samples over threshold) but this has some overheads per possible hit and because of this it would not be an improvement if the threshold was skimming the noise.

random trig from TI, block trigs, measure ratio of ack/declined
might be limited to 250khz.  


Beni : pmt+light leak more realistic trigger.

Cody sets low thres & masks channels so have defined occupancy.


Sergey says TS firmware busy is implemented but not tested.  Will look to see which versions of the TI and TS firmware we have.  They may have been customised.
Sergey will look to see which versions we have.

can update firmware 
set registers in TS.


Cody & Ben will measure delay times.  w Sergey.

notify fernando switch on LV only
masking
distribution of random triggers
beni set up true random pmt trigger

notify sascha before cody & sergey will update one crate.  

dave abbott also wants to test newer stuff


readback mode disabled when short of space but could be reenabled for test version w one mode.

trig2.  trigger analog pulser, vary time of trig1&2