Minutes 21/03/00 (Birmingham)

Present: A. Baird, J. Dowell (in part), Y. Fleming, D. Mercer, P. Newman, D. Sankey, A. Schoening, R. Staley

Minutes of this meeting consist of postscript files of talks (where available), some pointers to other bits of information and a few notes.

Update on L2 / L3 (A. Schoening)

Andre' summarised the latest situation with the level 2 and 3 systems and with the overall project. Some points that are worth noting from Andre's talk and the surrounding discussion
  • SCS have now produced a final costing for the L2 system (the feasibility study can be found from here ). - The costs were a little more than expected. However, with David Mueller paid by ETH Zuerich to work for 2 years at SCS, the overall costs become 235k SwF for hardware and 400k SwF for manpower. This matches the figures in the FTT proposal, though not all moneys have yet been obtained from funding bodies.
  • A first plan now exists for level 3. Details (from a talk by Jurgen Naumann) can be found here as ps or pdf . The planned LVDS daisy-chain caused some discussion.
  • Andre' has investigated the possibility of adding FPGAs at level 2 to make fast decisions based on the (pre-DSP?) list of tracks. A first attempt at simulating an invariant mass combination showed that we have time for 1000 mass combinations with one APEX 20k400. - This would be enough to search for D* in events with <~ 30 tracks. It would certainly be enough to make e.g. pt sums. More investigations of the precision obtained etc are needed.
  • A reminder!... As things stand, we plan to keep the DCr-phi trigger in place, even when we have a L1 FTT trigger. This has implications for the design of the plug-through card.
  • The level 2 and 3 groups are aiming to deliver prototypes for October 2000, which is a lot earlier than the present L1 prototype aim. - The question is what (if anything) can we provide in time for October?

Level 1 Front End (All)

Most of the meeting was taken up with discussion of the algorithm and how it could be realised in hardware.

The most recent block diagrams from Adam / Dave were shown. These can be found here and will be updated soon.
Adam is presently assuming that the ADC card expects 8-bit input at 80 MHz. A final decision is needed on whether to use encoded (with load balancing) or unencoded mode CAMs or just simple Look Up Tables.

Andre' gave considerable detail on his own level 1 ideas. His talk is here as ps or pdf

For reference, an earlier talk by Andre on level 1 (October 99) can be found here as ps or pdf This contains lots of info on where to place pivot layers etc. Also note from here the result that the phi and kappa coordinates associated with a valid track segment change within the period of validity even at 20 MHz synchronisation frequency

Unless anyone objects quickly, the following will soon become a `decision'!..
  • In contrast to earlier minutes, we now plan to include all four trigger groups in the L1 trigger. (including the CJC2 layers). This will be essential from an efficiency /redundancy point of view and will help us ensure that essentially the same conditions are required at L1 and L2 (thereby making efficiency calculations etc much easier). This has serious implications for the layout of the crates / moving around of the data. Some block diagrams (Andre') showing how the data could be moved into the L1 trigger can be found under `Level 1 Triggering I/O ....' here

Proposal to use ASIC Readout Receiver Chip (A. Schoening)

Another interesting possibility was raised by Andre'.... - An ASIC has been proposed by a company founded by Thom Wolff (DCr-phi trigger designer). This ASIC would essentially replace the FADCs and the Q-t extraction (including the z-coordinate). A few details can no longer be found here (removed at request of Thom Wolff).
Clearly such a custom chip could simplify the L1 design considerably. However, several important questions and possible objections were raised (Adam etc). - Most importantly, the flexibility and reprogramming possibilities of the currently proposed FPGA solution are lost. Can e.g. recalibrations be easily done? There are also doubts about whether it is physically possible to pass the many signals from all necessary CJC channels into the ASICs.
To help us understand the proposed ASIC better and to assess whether it will work for our purposes, it is propoed to invite Thom Wolff to one of the next FTT meetings (5th April video conference or 9th May in B'ham, probably 5/4).

Level 1 Trigger

The kappa-phi matching between different layers was discussed at length. Some collected thoughts of relevance to the design of the L1 trigger segment linking....
  • The kappa-phi region covered by a single CJC region has a very strange shape in kappa-phi space when phi is measured from the vertex. When phi is measured from the apex, the kappa-phi space is rectangular.
  • At (16 x 60) kappa x phi granularity, 1 CJC cell corresponds to two phi bins (i.e. one either side of the wire).
  • In the general case, there is a `phase shift' in the phi bins between different layers. - Unfortunately they do not line up neatly, so account will have to be taken of this when defining histograms for linking.
  • As mentioned above, the kappa-phi positions of a valid segment change from bunch crossing to bunch crossing.

Pivot Layer Studies (Y. Fleming)

Yves has been thinking about the question of how best to exploit the pivot layer technique. He has code working which takes a given pattern in the shift registers (including the case where cell boundaries are crossed), decides whether the pattern is valid (using FTTEMU), then propagates that pattern to the point where the pivot element is struck to check the pattern is not lost (e.g. because one of the hits has clocked off the register, or else has not yet appeared because the drift distance is long).
This code is now being used to assess where to place the pivot element and how long the register should be. The proposed means of assessing this question is .....
  • Determine how far into the shift register to place the pivot element. This is defined as the point where no valid masks are lost because one of the hits has not yet clocked onto the register.
  • With the pivot element position decided, next work out how long the registers have to be. - This is defined as the length at which no valid masks are lost due to the earliest arriving hits clocking off the register.
The most extreme cases always happen where the track crosses a cell boundary (>~ 1 microsec - max drift time difference between hit arrival times). To account for this possibility, it is proposed to have at least two pivot elements.

Most Urgent Questions

A very important deadline is approaching!
By the end of April, we are asked to demonstrate to the DESY PRC that the track segment finding can be done inside the available 2 microsecs.
First attempts at Quartus simulations are thus needed quickly! The first aim should just be to get a feel for the number of cycles required for each operation. We are asked to report at the meeting on April 5th.

The following open questions remain to be answered (among many others). ....
  • Interfaces with L2 (VME?) - Adam, Dave, Scott to discuss with SCS?
  • Should we use the e-vision readout chip?
  • How are we going to read this thing out?
  • How do we plan to calibrate the CJC and how often does this need to be updated?
  • Should data transmission to L1 trigger / L2 be encoded / unencoded / LVDS / optical?...

Next meetings

5th April: Video conference DESY - RAL, including plans to answer PRC breakpoint - demonstrate L1 segment finding can be done in time.
9th May: Full level 1 meeting (Birmingham)

Compiled by P. Newman, 27/3/00