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Using 2 boards as a 4 channel/synchronising triggers

Posted: Wed Mar 07, 2018 3:51 pm
Hi. I have a project where I'm going to use 2 boards "nailed" together mechanically to take readings of 4 different signals on the 2x 2x IN signals (hope that makes sense). As the signals will all be related, I would like to be able to synchronise the triggers so that the 2 boards trigger off the same input event, where the input event relates to a real world analogue input I am seeing.

Is there a way using the browser supplied apps I can achieve this? I can wire into the external triggers on the E1 connectors, but what I can't do is use a common signal generator onto the 2 external triggers to trigger at regular times on both boards. It could be of the form "is trigger condition met? If yes then set DIOn high" where DIOn would then be wired into the second board's external trigger pin. The issue here is that I don't really have the time to get a code environment up and running to control the GPIO and as this is taking measurements underwater I won't be able to change anything on the board once the readings are going (it won't be getting wet, don't worry!)

Thanks in advance.

Re: Using 2 boards as a 4 channel/synchronising triggers

Posted: Thu Mar 08, 2018 11:28 am
by amike88

i don't see a way to do it with stock aps.

what is the frequency of the signals that you are trying to capture?
Depending on your signals I see two simple options here:
  1. write a script that reads GPIOs and then writes to another GPIO, this will probably have a delay in ~ 100 ms. This is a guess on my part.
  2. modify FPGA code to connect external trigger GPIO to other GPIO to be used as trigger generator. Here the delay will be 8 ns.

Then there is also a this project that synchronises a cluster of red pitayas, which is bit more time consuming to implement.

Re: Using 2 boards as a 4 channel/synchronising triggers

Posted: Fri Mar 09, 2018 2:52 pm
Thanks for the reply. It's expected to be 20kHz in this case. I think I was hoping to achieve your option 2 without writing any code. It would be nice to be able to control the GPIO as well as the OUT signals based on IN trigger events 'out of the box'. Would open up a world of joy for me.

Re: Using 2 boards as a 4 channel/synchronising triggers

Posted: Mon Mar 12, 2018 10:18 am
by amike88
Actually I think there is a way. Sorry it didn't come to me before.

What you could do is use jupyter.

Then take the Logic generator example and set it to generate a pulse whenever Logic analyser gets triggered. Not sure about the delay but it should much closer to 8 ns. Also the delay between input trigger and pulse generation will be constant, which means that you can offset pre and post trigger amount of data in the second RP to align data. The example for logic generator is installed on RP with the latest OS.

In case you do not have the latest OS installed, follow this instructions.

hope this helps