Eclipse Community Forums: 4DIAC - Framework for Distributed Industrial Automation and Control » External event queue is full, external event dropped!

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External event queue is full, external event dropped! [message #1844591]

Fri, 17 September 2021 04:15

Eclipse User

Hi, i am trying to toggle one GPIO of BeagleBoneBlack at 1 kHz frequency. I simply created an application like E_CYCLE block triggers E_T_FF and output of flip flop toggles gpio using QX block. When i decreased cycle time below 100 ms i get following error from forte runtime:
...
ERROR: T#2826556356294: External event queue is full, external event dropped!
ERROR: T#2826556404211: External event queue is full, external event dropped!
ERROR: T#2826557540169: External event queue is full, external event dropped!
ERROR: T#2826558697003: External event queue is full, external event dropped!
...

Appereantly QX blocking more the forte more than 1 ms and causes that events not handled in time. Do you have any ide how can i solve this problem?

Uname output:
debian@beaglebone:~$ uname -a
Linux beaglebone 4.19.94-ti-r42 #1buster SMP PREEMPT Tue Mar 31 19:38:29 UTC 2020 armv7l GNU/Linux

Attachment: toggle.png
(Size: 15.86KB, Downloaded 96 times)

Re: External event queue is full, external event dropped! [message #1844605 is a reply to message #1844591]

Fri, 17 September 2021 09:21

Eclipse User

Hi,

first of all we have now a fix in the 2.0.x branch of 4diac FORTE that handles the external event dropped issue a bit more gracefully and such 4diac FORTE is not completely dying. However this will only partly improve your situation.

One problem we noticed is that the QX blocks are not super efficient. However we haven't had time to loook into it for improving it. I think first some measurements are needed to find out where the problem in QX is. Also if someone has time it would be intersting to look at other ways to access GPIOs on the BBB.

What you can try is to give your 4diac FORTE a higher priority. For that you can use the chrt command: https://www.cyberciti.biz/faq/howto-set-real-time-scheduling-priority-process/

I hope this helps and please let us know if you have some findings.

Cheers,
Alois

Re: External event queue is full, external event dropped! [message #1844614 is a reply to message #1844605]

Fri, 17 September 2021 11:12

Eclipse User

Hi Alois,

Thanks for the quick response.

I changed the forte real time scheduler to SCHED_RR and priority to 99 but i still have event queue issue.

I noticed that when i remove QX block from my application it works fine. As you stated lower level access to gpio other than QX block may solve the the problem.

Kind regards,
Berkin

Re: External event queue is full, external event dropped! [message #1844624 is a reply to message #1844614]

Fri, 17 September 2021 15:23

Eclipse User

Hi,

to my understanding SCHED_FF should give you a bit more performance but I would not expect much.

Just to clarify one thing: you don't need to fully implement a QX block but you just need to implement an own processinterface class. You can use the sysfs (the current BBB GPIO impl) as starting point.

BR,
Alois

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