Can receiving data interfere with sending (ESP32)

[veitk]

Hi,

love your library!

On my ESP32 i sometimes have timing issues during sending. Instead of a 500ms signal i get something like 900ms.
I have multiple ESP32 receiving this timing-error at the same time so the problem has to be on the sending side.

My receiver (on the same board as the sender) probably always captures my outgoing signal but i ignore that in my code.
Since my usecase is very timing critical my receiver is always on (i saw your repeater examples where you disable the receiver) - i know my selfmade manchester encoding is only 11ms but well ...

So my question:
Do you think that the receiving of the signal could be corrupting the sending?

And yes, wifi and mqtt is running as well as some rgb-leds with fastled and two servos :)
This could be a problem as well. But receiving works perfect with every other component running, sending works like 90-95% of the time.

sorry for my weird english ;-)

[crankyoldgit]

Sending will be quite susceptible to load on the CPU in the form of background tasks. That said, a delay of 400ms is quite long. Far longer than I'd expect. Are you sure you're not talking about uSeconds (us)? Most IR messages are sub-200ms. So a message/delay of 900ms (almost a second) is a sign something is very wrong. It's a VERY VERY long time in the IR world.

Receiving a signal is relatively simple (in the order of 100 CPU instructions per pulse) and interrupt driven. Decoding (decode()) a captured signal on the other hand is VERY cpu-time expensive. Sending CPU bit-bangs the GPIO to produce the signal/message and a message can be quite long (i.e. in the order of 100+ mSeconds (ms)) and it shouldn't relinquish the CPU (i.e. no delay()s or yield()s in the message bodies unless there is a gap larger than 16ms.) so should only be affected by interrupts.

Have you tried running the tasks on different CPUs on the ESP32? CPU 0 (default) will be quite loaded with Wifi etc.

As for running IR send & receive at the same time. It shouldn't cause that much of a problem. The main issue is receiving an unwanted signal.

[crankyoldgit]

Also see the FAQ: https://github.com/crankyoldgit/IRremoteESP8266/wiki/Frequently-Asked-Questions#some-other-library-eg-bluetooth-is-interfering-with-irsend-what-can-i-do-esp32

[veitk]

Yes sorry of course it is not 400ms, the raw signals have values of 500 or 1000 (so microseconds) and the complete signal is 11ms long.
I only use the raw decoding and sending and decode the signal myself, it is quite similar to your lasertag decoding.

I will create a test setup without wifi/mqtt and all of my led light-show disabled and will get back to you - maybe my findings can help others.

[crankyoldgit]

Phew. A delay of 400us I can easily imagine. Some thing (fast-led or servos) is probably generating an interrupt during sending, thus stealing away the CPU for that delay/extended time.
Hence that FAQ item. You probably want to run the send on the second (1) CPU which in theory is probably the least loaded, thus best for generating a better timed signal.