Trigger and Digitizer Setup

Triggers and digitizers

Digital Gammasphere uses the same trigger and digitizer modules that Gretina does, but the firmware is completely different.

Setting up Triggers in Digital Gammasphere

The general rule for setting up triggering in Digital Gammasphere (and DFMA, and GRETINA) is that when initializing, you have to work your way down from the Master Trigger to the digitizer to lock timestamps, BUT THEN you must WORK YOUR WAY BACK UP to get triggers working. This "working your way back up" occurs in the following steps:

1. Set up digitizers to transmit actual discriminator data to the Routers.
• This should happen by default. Common problems are accidentally disabling the SERDES or setting the bit that sends SYNC patterns instead of real data.
2. Set up the digitizers to assert the discriminator bit for an appropriate time (e.g. 100ns).
• This number is set channel-by-channel in every digitizer. A script is recommended.
3. Verify that the Routers lock onto the data from all digitizers. Use the counters of the Router to insure that no channel is dropping in and out of lock.
4. Ignore the X-plane and Y-plane map registers. These are used in DFMA only.
5. Load the CLEAN_DIRTY_CONTROL register of each Router (address 0x8CC) with the appropriate mapping. The Router will report two sums to the Master called the 'X' sum and the 'Y' sum. The CLEAN_DIRTY_CONTROL register selects which sum reports which condition. Bits 7:4 control the 'Y' sum and bits 3:0 control the 'X' sum. The allowable selections are
   • 0001 to send the 'clean' sum
   • 0010 to send the 'dirty' sum
   • 0100 to send the 'module' sum
6. Then load each Router's TSCATTER_DELAY register (address 0x08C8) with the time after the Ge hit during which the corresponding BGO hit can mark the Ge hit as 'dirty' - that is, the Scattering Time.
• A value of 30 (or 600ns) is typical. Each count is 20ns.
7. You may use the Channel FIFOs of the Router to look at the actual data coming from each digitizer. You should expect to see the 10 digitizer bits in bits 9:0.
8. You may use Monitor FIFO 4 of the Router to look at the actual data being sent from the Router to the Master. You should expect to see the 'X' sum
9. Repeat all steps above for every Router in the system.
10. Now proceed to setting up the Master Trigger. First verify using the channel FIFOs that the Master is getting the data from the Routers.
• A common error is to forget to turn off the SYNC bit in the LINK_LRU_CTRL register of the Router, so that the data isn't actually sent to the Master.
11. Next, set the multiplicity thresholds for the 'X' and 'Y' sums within the Master Trigger.
12. Then enable the appropriate trigger algorithms in the Master Trigger by setting bits in the Trigger Mask register.
• Enabling both the SumX and SumY triggers at the same time has the effect of an OR; if either sum is satisfied a trigger occurs.
• If both trigger types are enabled and both sums are satisfied two triggers are issued, but since they have the sime timestamp it is highly likely that both will select the same event.