I2S and WiFi interference

[vortigont]

Hi all,
inspired by #256 (but not necessary related)
Has anyone ever noticed generic WiFi issues with esp32 when I2S engine running at clock speed 10 and specially 20 MHz?
I remember facing this severely sometime ago. With running i2s a simple pinging board's IP becomes spiky with a huge jitter. For quite a while I was even thinking that some of my boards are faulty. Than using Hallard's shield made life a little bit easier, so I forgot about it. Currently I do not have any LED boards at hand, so can't test or confirm it. Just want it to be here to be confirmed or dis-proofed by others.
Maybe tweaking clock speed to something other than multipliers of 10 MHz could make a difference.

Cheers!
cc @mrfaptastic @solhuebner

[mrcodetastic]

Interesting. So you're thinking this isn't a SoC DMA / silicon issue causing internal bandwidth contention with the WIFI stack, but actually RF noise generated by GPIO output possibly impacting WiFi performance?

So, potentially something to do with harmonics?

[board707]

So you're thinking this isn't a SoC DMA / silicon issue causing internal bandwidth contention with the WIFI stack, but actually RF noise generated by GPIO output possibly impacting WiFi performance?

I don’t think that this is RF noise, since on the other lib the output to the matrix does not interfere with Wi-Fi.
I just checked that on PxMatrix I can stream lowres video to 64x32 panel via ESP32 WiFi with 25 fps with only minor artifacts

[solhuebner]

Interesting question. I will put it on my todo but might only get to it next week.

[vortigont]

yep, might be that way. First I suspected that something is wrong here when working with my testbed. Periodic UI updates were quite unstable, sometime better in AP mode, sometimes not. Do not remember if it was before we dropped clock rates other than 10/20 MHz or later. But it definitely worth a closer look next time.

[vortigont]

Found similar issue, just leave it here for crossreference espressif/arduino-esp32#5834

[ergindemir]

What kind of devkit/pcb are you using? Most devkits are poorly designed with signal traces on the bottom of the pcb.

[vortigont]

It was Wemos D1 esp32 with and without Hallard's shield.
Boards are OK, since I've used it before for other projects with no similar issues.

[ergindemir]

Ideally all signal traces should be on the top with pure ground on the bottom plane. No gpio pins next to the antenna. In addition the board should come with a proper regulator, high output capacitor and decoupling capacitor next to the module. Finally, you should check if your board uses a genuine or knock off wroom module. If you can eliminate all these factors you may suspect that the 12th or 24th harmonic of the i2s signal causes the issue. From my experience devkit v1 module works fine despite knock off module, low output cap, few signal traces on the bottom and few pins next to the antenna. Another devkit with 38 pin which suffers from all causes above has severe wifi issues.