Wemos C3 Mini should pre-set tx_power to 8.5

[jepler]

CircuitPython version

main

Code/REPL

n/a

Behavior

As reported by multiple users, with the power-on default tx_power, the board does not successfully connect to wifi (#6540 #9058 (comment) and probably others) but does work if boot.py executes wifi.radio.tx_power=8.5.

Description

No response

Additional information

The board init routine should set tx_power=8.5 by default, without needing lines in boot.py.

[bill88t]

I did a bit more digging.
The reason tx_power=8.5 is needed is not because of C3, but because of the type of antenna the board is using.

The common PCB antennas commonly on esp modules are what we most have.
However here and a bit of time I noticed some of my boards did not connect to one specific network.
Those boards all had 3D antennas (and are not C3's):

Then I got a MakerGo ESP32-C3 SuperTiny from aliexpress, that absolutely did not connect to any network.
That has a ceramic style antenna:

Setting the power on all of these, fixes that one network on the 3D antennas, and the supertiny entirely.
They all connect to every network I have. (Thinkpad, sbc intel wifi, phone hotspot, another esp32s3, an old router wifi - the one 3d antennas didn't originally connect to)

Furthermore, even the traditional pcb antennas seem to work fine with tx_power=8.5.
So it would probably be wise to set that as the default value.
It may not be optimal for range, but the alternative of going on every board that has a ceramic or 3d antenna and configuring it on board_init() doesn't sound all that better honestly.
It would ensure maximum compatibility.
For better range, the users are free to change that back during runtime.

Curiously I should also note, I have some boards with ceramic antennas that work fine with default tx_power.
The issue is probably related to a variant / manufacturer of em.

[dhalbert]

It appears from reading the documentation, though I am not sure of this, that wifi.radio.tx_power=8.5 may be lowering the max power from its default. Would you be willing to do some testing to fetch and print out the power before and after the setting and see how its changed? It might get printed before USB is ready, so you could ESP_LOGI() it, or else turn off wifi workflow and do import wifi by hand to see the print.

[bill88t]

@dhalbert The current default is 20.0, set by the "default wifi settings" from idf as far as I can tell.
So yes with 8.5 it's less than half power.
But that's what works on all the antenna types.
Compatibility vs range.

And besides, the tiny ceramic antenna did connect through closed doors to an AP 3 rooms away. It's honestly fine.

Also, as I already mentioned, for those who need the range, it's a settable value. They can crank it all the way.
However, the default should be what works on every board, every antenna type. Even if suboptimally.

It may be worth testing more values and antenna types though.

[karlfl]

So, I took some time to perform some tests using the station example from the ESP-IDF. I discovered that my QTPY C3 would effectively connect up through power values of 18dBm (72 in the ESP API) but would never connect using the highest (and default) power of 20dBm (80 in ESP API). Lower values would connect fairly well, but 18 seemed to connect within 1 or 2 tries every time.

When I was digging into the ESP WIFI API, I discovered that you have to call this after wifi has started or it will error. I then returned to the Circuit Python code (and reviewed the PR from @bill88t, which gave me good insight into where wifi start up was being called. Thanks Bill!). I then ran a few experiments within a cp build. I discovered that placing the code in ports/espressif/common-hal/wifi/__init__.c at the end of common_hal_wifi_init() seemed to prove successful. Other places I tried this didn't seem to work, most likely because wifi wasn't started yet. There is probably a better place for this logic, but hopefully this gives you guys some insight into what I was able to get to work.

Web Workflow comes up now without any boot.py modifications. I plan to test this against some other wifi code (i.e. AP, web server, etc.) to see if all that works too.

Here's a snippet showing my change...

void common_hal_wifi_init(bool user_initiated) {
    wifi_radio_obj_t *self = &common_hal_wifi_radio_obj;

    if (wifi_inited) {
        if (user_initiated && !wifi_user_initiated) {
            common_hal_wifi_radio_set_enabled(self, true); //<--  this starts radio, but may not be called at the right time
        }
        return;
    }
    wifi_inited = true;
    wifi_user_initiated = user_initiated;
    common_hal_wifi_radio_obj.base.type = &wifi_radio_type;

...

    // set station mode to avoid the default SoftAP
    common_hal_wifi_radio_start_station(self);
    // start wifi
    common_hal_wifi_radio_set_enabled(self, true);  // <-- radio has to be started before you can set the max power
    common_hal_wifi_radio_set_tx_power(self, 18); // <-- 18dBm anything higher won't be successful (QTPY C3)

}

[bill88t]

I feel like what's happening is that we're overpowering the antennas. It may be too high values have bad signal reception too.
I will create a test program (that reads rssi too) and test some more values, hopefully tonight.

[bill88t]

It would be possible to detect error code 2 and recursively reduce power and retry.
But that would take too long (in runtime) and take flash space.

[bablokb]

@karlfl

discovered that my QTPY C3 would effectively connect up through power values of 18dBm (72 in the ESP API) but would never connect using the highest (and default) power of 20dBm (80 in ESP API).

Nice insight. A few hours too late for me: I just replaced shortly before your post the onboard ceramic antenna on my QTPY C3 with a (very!) cheap external antenna and had a good and stable connection at once. Before it didn't even find all available networks when trying a scan.

[dhalbert]

I wonder what the reason for the problem with the chip antennas is. I did some websearching and did not find any clear discussion. Maybe:

1. chip antenna has losses, is heating up, causing reduced performance
2. chip antenna is mismatched and higher reflected power due to higher SWR is affecting RF output stage