MarkRivers
commented
3 years ago I measured the total time to collect 2000 mapping points with TriggerRising mode as a function of the external trigger frequency. These were all done with 4096 channel spectra and 8 boards.
| Trigger frequency (Hz) | Expected time (s) | Actual time (s) |
|---|---|---|
| 100 | 20 | 41.5 |
| 80 | 25 | 43.0 |
| 60 | 33.3 | 43.0 |
| 50 | 40.0 | 55.5 |
| 40 | 50 | 57.3 |
| 30 | 66.7 | 71.6 |
| 25 | 80 | 84.0 |
| 20 | 100 | 100.0 |
It can be seen that only when the frequency is 20 Hz or less (50 ms period) does the acquisition time match the expected execution time. At that rate the boards all complete acquisition at the same time, and they all return the spectra at about the same rate. At any higher rate the board 7 completes acquisition significantly later than board 0.
lucagrittiniXGLAB
I have modified the test_mapping program so that it prints the elapsed time since start_map was called on each output message. This allows evaluating the performance.
I used this command to collect data in FreeRunning mode with 4096 channel spectra, 10 ms acquisition time, 2000 mapping points. This is exactly 800 spectra/s.
The expected time for this acquisition to complete is 2000 * 0.010 seconds = 20.0 seconds.
This is the end of the output.
It worked exactly as expected. All boards completed acquisition at the same time, and the total acquisition took 20.15 seconds, very close to the expected time.
This is the same test, except with TriggerRising rather than FreeRun. I used an external trigger with a frequency of 100 Hz, e.g. 10.0 ms period. The pulse generator was started some time after the call to start_map. The first time there was a non-zero number of available spectra allows estimating this time delay as 1.01 seconds.
A number of things are wrong:
I have not seen any documentation that suggests that the performance with triggered mode should be worse than with free running mode.
Today's APS presentation said 4096 channels can run at 800 spectra/s total from a Dante8, which is what these tests are doing. That mapping rate works fine in free-running mode, but not in triggered mode.