esp32: Fix setting WLAN channel in AP mode.

- Previously the call to esp_wifi_set_channel() would be immediately
  overridden by calling esp_wifi_config(...) with the previous channel set.

- AP interface doesn't seem to need more than esp_wifi_config(...) to work.
  It will automatically configure 40MHz bandwidth and place the secondary
  channel using similar logic to what was being explicitly calculated here.

- However, calling esp_wifi_set_channel() on the STA interface is necessary
  if using this interface with ESP-NOW (without connecting to an AP). So
  the esp_wifi_set_channel() call is kept in for this purpose. Without
  this, tests/multi_espnow/70_channel.py fails.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

Author: projectgus

ports/esp32/network_wlan.c

@@ -549,21 +549,38 @@ static mp_obj_t network_wlan_config(size_t n_args, const mp_obj_t *args, mp_map_
                         break;
                     }
                     case MP_QSTR_channel: {
-                        uint8_t primary;
-                        wifi_second_chan_t secondary;
-                        // Get the current value of secondary
-                        esp_exceptions(esp_wifi_get_channel(&primary, &secondary));
-                        primary = mp_obj_get_int(kwargs->table[i].value);
-                        esp_err_t err = esp_wifi_set_channel(primary, secondary);
-                        if (err == ESP_ERR_INVALID_ARG) {
-                            // May need to swap secondary channel above to below or below to above
-                            secondary = (
-                                (secondary == WIFI_SECOND_CHAN_ABOVE)
-                                ? WIFI_SECOND_CHAN_BELOW
-                                : (secondary == WIFI_SECOND_CHAN_BELOW)
+                        uint8_t channel = mp_obj_get_int(kwargs->table[i].value);
+                        if (self->if_id == ESP_IF_WIFI_AP) {
+                            cfg.ap.channel = channel;
+                        } else {
+                            // This setting is only used to determine the
+                            // starting channel for a scan, so it can result in
+                            // slightly faster connection times.
+                            cfg.sta.channel = channel;
+
+                            // This additional code to directly set the channel
+                            // on the STA interface is only relevant for ESP-NOW
+                            // (when there is no STA connection attempt.)
+                            uint8_t old_primary;
+                            wifi_second_chan_t secondary;
+                            // Get the current value of secondary
+                            esp_exceptions(esp_wifi_get_channel(&old_primary, &secondary));
+                            esp_err_t err = esp_wifi_set_channel(channel, secondary);
+                            if (err == ESP_ERR_INVALID_ARG) {
+                                // May need to swap secondary channel above to below or below to above
+                                secondary = (
+                                    (secondary == WIFI_SECOND_CHAN_ABOVE)
+                                    ? WIFI_SECOND_CHAN_BELOW
+                                    : (secondary == WIFI_SECOND_CHAN_BELOW)
                                     ? WIFI_SECOND_CHAN_ABOVE
                                     : WIFI_SECOND_CHAN_NONE);
-                            esp_exceptions(esp_wifi_set_channel(primary, secondary));
+                                err = esp_wifi_set_channel(channel, secondary);
+                            }
+                            esp_exceptions(err);
+                            if (channel != old_primary) {
+                                // Workaround the ESP-IDF Wi-Fi stack sometimes taking a moment to change channels
+                                mp_hal_delay_ms(1);
+                            }
                         }
                         break;
                     }