What is the point of the coex feature?

[Easyoakland]

In my application I have both wifi and ble features enabled, but not coex. In testing both wifi and bluetooth seem to work fine (while using both concurrently). What is the purpose of the coex feature (which I have not enabled)?

If it helps this is the relevant section in my Cargo.toml

esp-wifi = { version = "0.13.0", features = ["esp32",
    # "utils",
    "wifi", "sniffer",
    "ble",
    #"coex", # This actually seems to break coex? coex (bluetooth and wifi simultaneously) works fine without enabling this
    "log-04",
] }

[bjoernQ]

In #3079 (comment) we noticed that you actually can use both more or less at the same time w/o enabling coex - maybe because the protocols are "forgiving" in regards of transmission errors.

Especially on ESP32 there were some bugs with coex which are fixed on main but not released yet: #3403 - with that coex should work correctly

[Easyoakland]

So how does the antenna time-slice without coex? What's the advantage of the feature? Higher throughput? Is the feature related to CONFIG_ESP_COEX_SW_COEXIST_ENABLE? The espressif docs seem to imply hardware by default splits time in half for both. Is that true for esp-wifi without enabling the feature?

Also, that linked comment doesn't describe the situation accurately enough. Both wifi and Bluetooth can be used simultaneously under high load. In fact, the wifi throughput seems to suffer only 50% or less while benchmarking wifi throughput while simultaneously subscribed to an active GATT characteristic.

[bjoernQ]

Yes - the coex feature basically serves the same purpose as CONFIG_ESP_COEX_SW_COEXIST_ENABLE

We probably should document that better, then.

[Easyoakland]

Do you know how the software multiplexes the antenna? It is unclear to me from the docs what algorithm is used in software when that setting is enabled.

[bjoernQ]

Not really unfortunately. From our point of view it's a black-box wiring callbacks from libcoex.a to the ble/wifi blobs and vice-versa

[Easyoakland]

Are you (or maintainers of ESP-hal in general) employed by espressif and expressif doesn't know? Or are you an outside entity?

[Dominaezzz]

Espressif Devs are under very strict hush hush rules when it comes to the WiFi/BLE radio.
If esp-idf docs don't have it, you won't be able to get it.