I modelled Xignal after PLCs that I used to work with earlier. I think the scan makes the system easy to reason about and I believe for many signals performance will be better. The current system implements:
io at scan rate x Hz
→
io image in memory
→
scan runner at y Hz
→
output image in memory
→
IO writer at x Hz
The good thing is you can have several IO devices at different rates and it doesn’t matter. Its very simple.
Even so, just recently I made a :triggered mode that reads the inputs, then runs the logic, then writes, based on events. You can still run slower io in the same mix though, in the old way.
I have done many test with threading though, and because these logic tasks are very lightweight, to get performance you need to match n threads to n CPU cores, something I would normally not consider in Elixir.
I didnt look into the new event based standards except very briefly. I don’t think these have been very successful to my knowledge, and I am not sure if they even make practical sense. Anyhow, that is not the system I wrote with Xignal. Maybe something to test for Yignal? Even for Modbus, values are often read in blocks, and many values woudn’t change… but you still need a way to inform each signal about time advancing?
to those PLCs). Live edits are essential in my eyes.