feat: nodes scan wifi channels during discovery

[jamienz]

When a node is performing the discovery process, it loops through an array of wifi channels and sends its broadcast on each channel. Its possible that the node sends a broadcast on one channel, and the host receives it despite being on another (due to the fact that wifi channels overlap?), so the host includes its channel in the response. The node then saves this channel in NVS.

[Johboh]

Thanks for you contribution @jamienz! I didn't expect anyone to use this over engineered library other than my self, given the sparse documentation :).

I'm going to cherry pick this and try it out, and I will leave some inline comments as well.

Do you know, how does the WiFi channel relate to the ESP-NOW channel? As we are setting here and here. E.g. if we should set this instead/also.

For my "statistics", do you use the ESP-IDF or Arduino library variant?

[jamienz]

Thanks for creating the EspNowNetwork library @Johboh!

When you do your testing of this PR, make sure that the WiFi network that the host is connected to is NOT on channel 1.

When the host is connected to a WiFi network, it will send/receive ESP-NOW messages on the same channel as that network (it can't send on a different channel). The node isn't connected to a WiFi network, so by default it will be on channel 1, based on my testing by adding the following code to the node before it sends it's discovery broadcasts:

uint8_t primary = 0;
wifi_second_chan_t second;
ESP_ERROR_CHECK(esp_wifi_get_channel(&primary, &second));
log("channel=" + std::to_string(primary), ESP_LOG_INFO);

The peer_info.channel is set to zero which means ESP-NOW messages will be sent on whatever channel is the current WiFi channel - for the host it will be the WiFi network channel, and for the node it will be 1. With the code currently in the main branch, everything will work well if the host is connected to a WiFi network on channel 1. this PR aims to support the host being on a channel other than channel 1.

I'm using PlatformIO/Arduino.

[Johboh]

Right, I was just thinking of what the point was with the channel field in the peer info. If I understand the documentation correctly, if set to 0 it will use same channel "which station or softap is on", otherwise if not zero it must be set to be "the channel that station or softap is on.". So if I'm not missing something, the channel is quite useless and could have been omitted in the ESP-now API?

[Johboh]

Added some comments! Sorry for being nit-picky, but I review PRs for a living :)

[Johboh]

(I moved some files around, but no change to the files themself, so a git pull --rebase should resolve the merge issue automatically)

[jamienz]

Thanks for the feedback. I'll make those changes tonight.

[Johboh]

Some minor comments left, and a failing clang-format (whitespace). If those are fixed, we are good to merge.

[jamienz]

Right, I was just thinking of what the point was with the channel field in the peer info. If I understand the documentation correctly, if set to 0 it will use same channel "which station or softap is on", otherwise if not zero it must be set to be "the channel that station or softap is on.". So if I'm not missing something, the channel is quite useless and could have been omitted in the ESP-now API?

Thats a good question. Its definitely not useless, its doing something, but I'll admit that I don't understand exactly what its doing - the documentation is incomplete in my opinion.

If peer_info.channel is assigned zero, and the Node wifi channel isn't explicitly set, and the Node doesn't connect to a wifi network, the wifi channel seems to be 1.

My WiFi access point is on channel 6 right now, and since the Host connects to that access point, it is on channel 6 also. So when the Node broadcasts on channel 1, the Host doesn't hear it. Setting the peer_info.channel on the Node to 6 doesn't work:
E (280) ESPNOW: Peer channel is not equal to the home channel, send fail!
The Node needs to be on Wifi channel 6 also.

See: espressif/esp-idf#9592. The important final comment from the Espressif guy is "ESP-NOW's channel should obey the STA/AP's channel". Which I interpret to mean:

• the Node's peer_info.channel needs to be 0, so that it uses the Node's WiFi channel (which needs to match the Host's WiFi channel)
• or the Node's peer_info.channel needs to be explicitly set to the WiFi channel

Leaving peer_info.channel=0 is the least-effort option.

[Johboh]

@jamienz There are three more inline comments that it looks like you are missing:
#1 (comment)
#1 (comment)
#1 (comment)

[Johboh]

I will go a-head and merge this one as I need myself (I will address outstanding comments and fix clang format). There is also an unrecoverable crash loop that can happen in the node that I will fix (and that I ended up with when testing). Will share the fix commit here.

[Johboh]

@jamienz FYI: 368aa09

[jamienz]

That's great @Johboh. I really appreciate your time in reviewing this, and for finishing it. Apologies for not getting back to this one sooner to finish off the final tasks.