Feb 2013

Date : 6 Feb 2013 (K.Allada)

We are now using the new FADC(v2) and a fixed pulser.

I did few more checks to find out why we are getting "data not ready" errors at trigger rates beyond ~250KHz (with PTW =75 samples). This is related to datascan becoming zero for few-tens-of-events/100 triggers, and this becomes worse as we go to higher trigger rates. When this happens the event is empty. And since we do blocking, we get a empty blocks. Blocksize is 100.

Also, note that the theoretical limit (from the excel sheet) with PTW=75 samples and FADC v2 is around ~430 kHz. We should be able to take this much rate with a fixed pulser.

From the routine tiSetTriggerHoldoff(1,40,0), the trigger limit, without additional deadtime, is 40*16=640ns (= 1.56MHz). So this is fine...we are not there yet.

Below is a table showing observed data rate from the Run Control GUI for different trigger rates. It seems like the data rate is saturating at ~5K Bytes/sec ( which is around 250 KHz) and that's when the datascan becomes zero (error).

run      trigger rate    observed event rate   observed data rate    error condition

1910      31 kHz         31 kHz                 ~600 Bytes/sec         no error
1909      85 kHz         85 kHz                 ~1500 Bytes/sec        no error
1908      121 kHz        121 kHz                ~2200 Bytes/sec        no error  
1907      168 kHz        168 kHz                ~3000 Bytes/sec        no error
1906      251 kHz        251 kHz                ~5000 Bytes/sec        no error
1905      315 kHz        315 kHz                ~5200 Bytes/sec        error
1904      434 kHz        434 kHz                ~5200 Bytes/sec        error

To check if disk is a limitation, I turned off writing to disk in the coda config. And I still see these errors. So disk may not be an issue. (adaq1 has 1.1 GB/sec speed)

Next is the network. We have 100MBits/sec (12.5 MBytes/sec). How can we max out at 5K Bytes/sec?