TAG V3.1 - esp_wifi_scan_start() in STA mode (IDFGH-619)

[caipiblack]

Environment

• Development Kit: self made
• Module or chip used: ESP32-WROOM-32
• IDF version: v3.1 (tag)
• Build System: CMake
• Compiler version: xtensa-esp32-elf-gcc (crosstool-NG crosstool-ng-1.22.0-73-ge28a011) 5.2.0
• Operating System: Linux
• Power Supply: external 5V

Problem Description

When we call esp_wifi_scan_start() in STA mode (connected to an acces point) we get this error:

W (167973) wifi: Now is connecting, user scan invalid now!

The result of esp_wifi_scan_start() is ESP_ERR_WIFI_TIMEOUT

The WiFi mode is: WIFI_MODE_STA

Expected Behaviour

The wifi scan must be started

Actual Behaviour

The wifi scan is not started and it returns the errors on the description

Questions

Is it possible to use this functions in STA mode (connected to an AP) ?

[liuzfesp]

Hi @caipiblack, ESP32 supports two kinds of scan: the connecting scan which is triggered by esp_wifi_connect() and the user scan which is triggered by esp_wifi_scan_start(). The connecting scan has higher priority than the user scan, in other words, the esp_wifi_scan_start() will fail if the station now is connecting to the AP and following log will be displayed:

W (167973) wifi: Now is connecting, user scan invalid now!

So it's expected behavior.

The most simple way to handle this cause is to delay sometime and call esp_wifi_scan_start() again. However this method doesn't make sense in following scenario:

1. esp_wifi_connect() is called and ESP32 station is connecting to an non-exist AP.
2. WiFi disconnected event is raised because the AP is not found, the WiFi event handler simply calls esp_wifi_connect() to reconnect the non-exist AP.
3. step 1/2 is repeated again and again.
4. esp_wifi_scan_start() is called.

If this is your case, you need to call esp_wifi_disconnect() to stop WiFi connection before esp_wifi_scan_start() is called, otherwise, esp_wifi_scan_start() will always fails.

For the return value ESP_ERR_WIFI_TIMEOUT, I think it's not accurate, we need to modify it, maybe it's better to return ESP_ERR_WIFI_FAIL etc.

You can refer to: wifi_doc for more info about scan.

BTW, are you use the block scan: esp_wifi_scan_start(config, true)?

[Alvin1Zhang]

@caipiblack Hi, would you help share if any updates for the issue? @liuzfesp how is the modification of return ESP_ERR_WIFI_FAIL etc? Thanks.

[Alvin1Zhang]

@caipiblack Thanks for reporting the issue. Would you please help share if any updates for the issue? Has your issue been fixed? Thanks.

[Alvin1Zhang]

Thanks for reporting, the fix is available at c05a39d, feel free to reopen if the issue still happens. Thanks.