Merge pull request #10762 from gschorcht/esp32_esp_wifi_fix

cpu/esp32: esp_wifi netdev driver

cpu/esp32/Makefile.dep

@@ -28,6 +28,7 @@ endif
 
 ifneq (,$(filter esp_wifi_any,$(USEMODULE)))
     # add additional modules used for any WiFi interface
+    USEMODULE += esp_idf_heap
     USEMODULE += esp_idf_wpa_supplicant_crypto
     USEMODULE += esp_idf_wpa_supplicant_port
     USEMODULE += esp_idf_nvs_flash

cpu/esp32/doc.txt

@@ -46,8 +46,9 @@
     2. [SPIFFS Device](#esp32_spiffs_device)
 8. [Network Interfaces](#esp32_network_interfaces)
     1. [Ethernet MAC Network Interface](#esp32_ethernet_network_interface)
-    2. [ESP-NOW Network Interface](#esp32_esp_now_network_interface)
-    3. [Other Network Devices](#esp32_other_network_devices)
+    2. [WiFi Network Interface](#esp32_wifi_network_interface)
+    3. [ESP-NOW Network Interface](#esp32_esp_now_network_interface)
+    4. [Other Network Devices](#esp32_other_network_devices)
 10. [Application-Specific Configurations](#esp32_application_specific_configurations)
     1. [Make Variable ```CONFIGS```](#esp32_config_make_variable)
     2. [Application-Specific Board Configuration](#esp32_application_specific_board_configuration)
@@ -108,8 +109,8 @@ The following table gives a short reference  in alphabetical order of modules th
 
 Module    | Default  | Short description
 ----------|----------|-------------------
-[esp_can](#esp32_can_interfaces) | not used | enable the ESP32 CAN device
-[esp_eth](#esp32_ethernet_network_interface) | not used | enable the ESP32 EMAC network device
+[esp_can](#esp32_can_interfaces) | not used | enable the CAN device
+[esp_eth](#esp32_ethernet_network_interface) | not used | enable the Ethernet MAC (EMAC) network device
 [esp_gdb](#esp32_debugging) | not used | enable the compilation with debug information for debugging
 [esp_hw_counter](#esp32_timers) | not used | use hardware counters for RIOT timers
 [esp_i2c_hw](#esp32_i2c_interfaces) | not used  | use the i2C hardware implementation
@@ -117,6 +118,7 @@ Module    | Default  | Short description
 [esp_now](#esp32_esp_now_network_interface) | not used  | enable the ESP-NOW network device
 [esp_spi_ram](#esp32_spi_ram) | not used |  enable SPI RAM
 [esp_spiffs](#esp32_spiffs_device) | not used  |  enable SPIFFS for on-board flash memory
+[esp_wifi](#esp32_wifi_network_interface) | not used  | enable the Wifi network device
 
 </center>
 
@@ -190,7 +192,6 @@ The RIOT-OS for ESP32 SoCs supports the following features at the moment:
 The implementation of RIOT-OS for ESP32 SOCs has the following limitations at the moment:
 
 - Only <b>one core</b> (the PRO CPU) is used because RIOT does not support running multiple threads  simultaneously.
-- <b>AP-based WiFi</b> is experimental and not stable.
 - RIOT modules <b>crypto</b> and <b>hashes</b> cannot be used together with modules <b>esp_now</b> and <b>esp_wifi</b>
 - <b>Bluetooth</b> cannot be used at the moment.
 - <b>Flash encryption</b> is not yet supported.
@@ -390,14 +391,15 @@ Optional features of ESP32 can be enabled by ```USEMODULE``` definitions in the
 
 Module | Description
 -------|------------
-esp_now | Use the built-in WiFi module with the ESP-NOW protocol as ```netdev``` network device, see section [ESP-NOW Network Interface](#esp32_esp_now_network_interface).
-esp_eth | Use the Ethernet MAC (EMAC) interface as ```netdev``` network device, see section [Ethernet Network Interface](#esp32_ethernet_network_interface).
+esp_can | Enable the CAN device, see section [CAN Interfaces](#esp32_can_interfaces).
+esp_eth | Enable the Ethernet MAC (EMAC) interface as `netdev` network device, see section [Ethernet Network Interface](#esp32_ethernet_network_interface).
 esp_gdb | Enable the compilation with debug information for debugging with [QEMU and GDB](#esp32_qemu_mode_and_gdb) (```QEMU=1```) or via [JTAG interface with OpenOCD](#esp32_jtag_debugging).
 esp_i2c_hw | Use the hardware I2C implementation, see section [I2C Interfaces](#esp32_i2c_interfaces).
 esp_idf_heap | Use the ESP-IDF heap implementation, see section [ESP-IDF Heap Implementation](#esp32_esp_idf_heap_implementation).
+esp_now | Enable the built-in WiFi module with the ESP-NOW protocol as `netdev` network device, see section [ESP-NOW Network Interface](#esp32_esp_now_network_interface).
 esp_spiffs  | Enable the optional SPIFFS drive in on-board flash memory, see section [SPIFFS Device](#esp32_spiffs_device).
 esp_spi_ram | Enable the optional SPI RAM, see section [SPI RAM Modules](#esp32_spi_ram).
-esp_can | Enable the ESP32 CAN device, see section [CAN Interfaces](#esp32_can_interfaces).
+esp_wifi | Enable the built-in WiFi module as `netdev` network device, see section [WiFi Network Interface](#esp32_wifi_network_interface).
 
 </center>
 
@@ -884,7 +886,7 @@ Please refer file ```$RIOTBASE/tests/unittests/test-spiffs/tests-spiffs.c``` for
 ESP32 provides different built-in possibilities to realize network devices:
 
 - <b>EMAC</b>, an Ethernet MAC implementation (requires an external PHY module)
-- <b>ESP WiFi</b>, usual AP-based wireless LAN (not yet supported)
+- <b>ESP WiFi</b>, usual AP-based wireless LAN
 - <b>ESP-NOW</b>, a WiFi based AP-less and connectionless peer to peer communication protocol
 - <b>ESP-MESH</b>, a WiFi based mesh technology (not yet supported)
 
@@ -906,6 +908,50 @@ Otherwise, the application has to add the ```esp_eth``` module in its makefile w
 @note
 The board has to have one of the supported PHY modules to be able to use the Ethernet MAC module.
 
+\anchor esp32_wifi_network_interface
+## <a name="esp32_wifi_network_interface"> WiFi Network Interface </a> &nbsp;[[TOC](#esp32_toc)]
+
+The RIOT port for ESP32 implements in module `esp_wifi` a `netdev` driver for
+the built-in WiFi interface.
+
+@note Due to symbol conflicts with the `crypto` and `hash` modules of RIOT
+in module `esp_idf_wpa_supplicant_crypto`, which is required by module
+`esp_wifi`, `esp_wifi` cannot be used for applications that use these modules.
+Therefore, module `esp_wifi` is not automatically enabled when module
+`netdev_default` is used. Instead, if necessary, the application has to add
+the module `esp_wifi` in the Makefile.
+
+```
+USEMODULE += esp_wifi
+```
+
+Furthermore, the following configuration parameters have to be defined:
+
+<center>
+
+Parameter          | Default                   | Description
+:------------------|:--------------------------|:------------
+ESP_WIFI_SSID      | "RIOT_AP"                 | SSID of the AP to be used.
+ESP_WIFI_PASS      | "ThisistheRIOTporttoESP"  | Passphrase used for the AP as clear text (max. 64 chars).
+ESP_WIFI_STACKSIZE | #THREAD_STACKSIZE_DEFAULT |Stack size used for the WiFi netdev driver thread.
+
+</center>
+
+These configuration parameter definitions, as well as enabling the `esp_wifi`
+module, can be done either in the makefile of the project or at make command
+line, e.g.:
+
+```
+USEMODULE=esp_wifi \
+CFLAGS='-DESP_WIFI_SSID=\"MySSID\" -DESP_WIFI_PASS=\"MyPassphrase\"' \
+make -C examples/gnrc_networking BOARD=...
+```
+
+@note The Wifi network interface (module `esp_wifi`) and the
+[ESP-NOW network interface](#esp32_esp_now_network_interface) (module `esp_now`)
+can be used simultaneously, for example, to realize a border router for
+a mesh network which uses ESP-NOW.
+
 \anchor esp32_esp_now_network_interface
 ## <a name="esp32_esp_now_network_interface"> ESP-NOW Network Interface </a> &nbsp;[[TOC](#esp32_toc)]
 
@@ -927,12 +973,16 @@ The following parameters are defined for ESP-NOW nodes. These parameters can be
 Parameter | Default | Description
 :---------|:--------|:-----------
 ESP_NOW_SCAN_PERIOD | 10000000UL | Defines the period in us at which an node scans for other nodes in its range. The default period is 10 s.
-ESP_NOW_SOFT_AP_PASSPHRASE | ThisistheRIOTporttoESP | Defines the passphrase (max. 64 chars) that is used for the SoftAP interface of an nodes. It has to be same for all nodes in one network.
+ESP_NOW_SOFT_AP_PASS | "ThisistheRIOTporttoESP" | Defines the passphrase as clear text (max. 64 chars) that is used for the SoftAP interface of ESP-NOW nodes. It has to be same for all nodes in one network.
 ESP_NOW_CHANNEL | 6 | Defines the channel that is used as the broadcast medium by all nodes together.
 ESP_NOW_KEY | NULL | Defines a key that is used for encrypted communication between nodes. If it is NULL, encryption is disabled. The key has to be of type ```uint8_t[16]``` and has to be exactly 16 bytes long.
 
 </center>
 
+@note The ESP-NOW network interface (module `esp_now`) and the
+[Wifi network interface](#esp32_wifi_network_interface) (module `esp_wifi`)
+can be used simultaneously, for example, to realize a border router for
+a mesh network which uses ESP-NOW.
 
 ## <a name="esp32_other_network_devices"> Other Network Devices </a> &nbsp;[[TOC](#esp32_toc)]
 

cpu/esp32/esp-wifi/doc.txt

@@ -7,12 +7,46 @@
  */
 
 /**
- * @defgroup        cpu_esp32_esp_wifi ESP WiFi netdev interface
+ * @defgroup        cpu_esp32_esp_wifi ESP32 WiFi netdev interface
  * @ingroup         cpu_esp32
- * @brief           WiFi AP-based network device driver
- *
- * This module realizes a netdev interface using the built-in
- * WiFi module and AP infrastructure.
+ * @brief           Network device driver for the ESP32 WiFi interface
  *
  * @author      Gunar Schorcht <gunar@schorcht.net>
+
+This module realizes a `netdev` interface for the built-in WiFi interface
+of ESP32. To enable the WiFi interface, module `esp_wifi` has to be used.
+
+@note Due to symbol conflicts with the `crypto` and `hash` modules of RIOT
+in module `esp_idf_wpa_supplicant_crypto`, which is required by module
+`esp_wifi`, `esp_wifi` cannot be used for applications that use these modules.
+Therefore, module `esp_wifi` is not automatically enabled when module
+`netdev_default` is used. Instead, if necessary, the application has to add
+the module `esp_wifi` in the Makefile.
+
+```
+USEMODULE += esp_wifi
+```
+
+Furthermore, the following configuration parameters have to be defined:
+
+Configuration Parameter | Description
+------------------------|------------
+ESP_WIFI_SSID           | SSID of the AP to be used.
+ESP_WIFI_PASS           | Passphrase used for the AP as clear text (max. 64 chars).
+ESP_WIFI_STACKSIZE      | Stack size used for the WiFi netdev driver thread.
+
+These configuration parameter definitions, as well as enabling the `esp_wifi`
+module, can be done either in the makefile of the project or at make command
+line, e.g.:
+
+```
+USEMODULE=esp_wifi \
+CFLAGS='-DESP_WIFI_SSID=\"MySSID\" -DESP_WIFI_PASS=\"MyPassphrase\"' \
+make -C examples/gnrc_networking BOARD=...
+```
+
+@note The Wifi network interface (module `esp_wifi`) and the
+\ref esp32_esp_now_network_interface "ESP-NOW network interface" (module `esp_now`)
+can be used simultaneously, for example, to realize a border router for
+a mesh network which uses ESP-NOW.
  */

cpu/esp32/esp-wifi/esp_wifi_netdev.c

@@ -11,7 +11,7 @@
  * @{
  *
  * @file
- * @brief       Netdev interface for the ESP WiFi AP-based communication
+ * @brief       Network device driver for the ESP32 WiFi interface
  *
  * @author      Gunar Schorcht <gunar@schorcht.net>
  */
@@ -72,18 +72,48 @@ extern esp_err_t esp_system_event_add_handler (system_event_cb_t handler,
 
 esp_err_t _esp_wifi_rx_cb(void *buffer, uint16_t len, void *eb)
 {
+    /*
+     * This callback function is executed in interrupt context but in the
+     * context of the wifi thread. That is, mutex_lock or msg_send can block.
+     */
+
     DEBUG("%s: buf=%p len=%d eb=%p\n", __func__, buffer, len, eb);
 
-    CHECK_PARAM_RET (buffer != NULL, -EINVAL);
-    CHECK_PARAM_RET (len <= ETHERNET_DATA_LEN, -EINVAL);
+    if ((buffer == NULL) || (len >= ETHERNET_DATA_LEN)) {
+        if (eb != NULL) {
+            esp_wifi_internal_free_rx_buffer(eb);
+        }
+        return ESP_ERR_INVALID_ARG;
+    }
 
     mutex_lock(&_esp_wifi_dev.dev_lock);
+    critical_enter();
 
+    /* copy the buffer and free WiFi driver buffer */
     memcpy(_esp_wifi_dev.rx_buf, buffer, len);
+    if (eb) {
+        esp_wifi_internal_free_rx_buffer(eb);
+    }
+
+    /*
+     * Because this function is not executed in interrupt context but in thread
+     * context, following msg_send could block on heavy network load, if frames
+     * are coming in faster than the ISR events can be handled. To avoid
+     * blocking during msg_send, we pretend we are in an ISR by incrementing
+     * the IRQ nesting counter. If IRQ nesting counter is greater 0, function
+     * irq_is_in returns true and the non-blocking version of msg_send is used.
+     */
+    irq_interrupt_nesting++;
+
+    /* trigger netdev event to read the data */
     _esp_wifi_dev.rx_len = len;
     _esp_wifi_dev.event = SYSTEM_EVENT_WIFI_RX_DONE;
     _esp_wifi_dev.netdev.event_callback(&_esp_wifi_dev.netdev, NETDEV_EVENT_ISR);
 
+    /* reset IRQ nesting counter */
+    irq_interrupt_nesting--;
+
+    critical_exit();
     mutex_unlock(&_esp_wifi_dev.dev_lock);
 
     return ESP_OK;
@@ -94,48 +124,82 @@ esp_err_t _esp_wifi_rx_cb(void *buffer, uint16_t len, void *eb)
  */
 static esp_err_t IRAM_ATTR _esp_system_event_handler(void *ctx, system_event_t *event)
 {
+    esp_err_t result;
+
     switch(event->event_id) {
         case SYSTEM_EVENT_STA_START:
             DEBUG("%s WiFi started\n", __func__);
+            result = esp_wifi_connect();
+            if (result != ESP_OK) {
+                LOG_TAG_ERROR("esp_wifi", "esp_wifi_connect failed with return "
+                              "value %d\n", result);
+            }
             break;
+
         case SYSTEM_EVENT_SCAN_DONE:
             DEBUG("%s WiFi scan done\n", __func__);
             break;
+
         case SYSTEM_EVENT_STA_CONNECTED:
             DEBUG("%s WiFi connected\n", __func__);
+
+            /* register RX callback function */
+            esp_wifi_internal_reg_rxcb(ESP_IF_WIFI_STA, _esp_wifi_rx_cb);
+
             _esp_wifi_dev.connected = true;
-            _esp_wifi_dev.event = SYSTEM_EVENT_ETH_CONNECTED;
+            _esp_wifi_dev.event = SYSTEM_EVENT_STA_CONNECTED;
             _esp_wifi_dev.netdev.event_callback(&_esp_wifi_dev.netdev, NETDEV_EVENT_ISR);
+
             break;
+
         case SYSTEM_EVENT_STA_DISCONNECTED:
-            DEBUG("%s WiFi disconnected\n", __func__);
+            DEBUG("%s WiFi disconnected from ssid %s, reason %d\n", __func__,
+                  event->event_info.disconnected.ssid,
+                  event->event_info.disconnected.reason);
+
+            /* unregister RX callback function */
+            esp_wifi_internal_reg_rxcb(ESP_IF_WIFI_STA, NULL);
+
             _esp_wifi_dev.connected = false;
-            _esp_wifi_dev.event = SYSTEM_EVENT_ETH_DISCONNECTED;
+            _esp_wifi_dev.event = SYSTEM_EVENT_STA_DISCONNECTED;
             _esp_wifi_dev.netdev.event_callback(&_esp_wifi_dev.netdev, NETDEV_EVENT_ISR);
+
+            /* call disconnect to reset internal state */
+            result = esp_wifi_disconnect();
+            if (result != ESP_OK) {
+                LOG_TAG_ERROR("esp_wifi", "esp_wifi_disconnect failed with "
+                             "return value %d\n", result);
+                return result;
+            }
+
+            /* try to reconnect */
+            result = esp_wifi_connect();
+            if (result != ESP_OK) {
+               LOG_TAG_ERROR("esp_wifi", "esp_wifi_connect failed with "
+                             "return value %d\n", result);
+            }
+
             break;
+
         default:
+            DEBUG("%s event %d\n", __func__, event->event_id);
             break;
     }
     return ESP_OK;
 }
 
-/** TODO better place
- * Default WiFi configuration, overwrite them with your configs
- */
-#ifndef CONFIG_WIFI_STA_SSID
-#define CONFIG_WIFI_STA_SSID        "RIOT_AP"
-#endif
-#ifndef CONFIG_WIFI_STA_PASSWORD
-#define CONFIG_WIFI_STA_PASSWORD    "ThisistheRIOTporttoESP"
-#endif
-#ifndef CONFIG_WIFI_STA_CHANNEL
-#define CONFIG_WIFI_STA_CHANNEL     0
-#endif
-
-#define CONFIG_WIFI_STA_SCAN_METHOD WIFI_ALL_CHANNEL_SCAN
-#define CONFIG_WIFI_STA_SORT_METHOD WIFI_CONNECT_AP_BY_SIGNAL
-#define CONFIG_WIFI_STA_RSSI        -127
-#define CONFIG_WIFI_STA_AUTHMODE    WIFI_AUTH_WPA_WPA2_PSK
+/* we use predefined station configuration */
+static wifi_config_t wifi_config_sta = {
+    .sta = {
+        .ssid = ESP_WIFI_SSID,
+        .password = ESP_WIFI_PASS,
+        .channel = 0,
+        .scan_method = WIFI_ALL_CHANNEL_SCAN,
+        .sort_method = WIFI_CONNECT_AP_BY_SIGNAL,
+        .threshold.rssi = -127,
+        .threshold.authmode = WIFI_AUTH_WPA_WPA2_PSK
+    }
+};
 
 static void esp_wifi_setup (esp_wifi_netdev_t* dev)
 {
@@ -171,19 +235,6 @@ static void esp_wifi_setup (esp_wifi_netdev_t* dev)
     /* TODO */
     #endif
 
-    /* we use predefined station configuration */
-    wifi_config_t wifi_config_sta = {
-        .sta = {
-            .ssid = CONFIG_WIFI_STA_SSID,
-            .password = CONFIG_WIFI_STA_PASSWORD,
-            .channel = CONFIG_WIFI_STA_CHANNEL,
-            .scan_method = CONFIG_WIFI_STA_SCAN_METHOD,
-            .sort_method = CONFIG_WIFI_STA_SORT_METHOD,
-            .threshold.rssi = CONFIG_WIFI_STA_RSSI,
-            .threshold.authmode = CONFIG_WIFI_STA_AUTHMODE
-        }
-    };
-
     result = esp_wifi_set_mode(WIFI_MODE_STA);
     if (result != ESP_OK) {
        LOG_TAG_ERROR("esp_wifi", "esp_wifi_set_mode failed with return value %d\n", result);
@@ -214,12 +265,6 @@ static void esp_wifi_setup (esp_wifi_netdev_t* dev)
     dev->connected = false;
 
     mutex_init(&dev->dev_lock);
-
-    result = esp_wifi_connect();
-    if (result != ESP_OK) {
-       LOG_TAG_ERROR("esp_wifi", "esp_wifi_connect failed with return value %d\n", result);
-        return;
-    }
 }
 
 static int _esp_wifi_init(netdev_t *netdev)
@@ -285,6 +330,7 @@ static int _esp_wifi_send(netdev_t *netdev, const iolist_t *iolist)
     }
 
     mutex_unlock(&dev->dev_lock);
+
     return ret;
 }
 
@@ -298,7 +344,7 @@ static int _esp_wifi_recv(netdev_t *netdev, void *buf, size_t len, void *info)
 
     mutex_lock(&dev->dev_lock);
 
-    uint8_t size = dev->rx_len;
+    uint16_t size = dev->rx_len;
 
     if (!buf && !len) {
         /* return the size without dropping received data */
@@ -356,9 +402,12 @@ static int _esp_wifi_get(netdev_t *netdev, netopt_t opt, void *val, size_t max_l
             esp_wifi_get_mac(ESP_MAC_WIFI_STA,(uint8_t *)val);
             return ETHERNET_ADDR_LEN;
         case NETOPT_IS_WIRED:
-            return true;
+            return false;
         case NETOPT_LINK_CONNECTED:
-            return dev->connected;
+            assert(max_len == 1);
+            *((netopt_enable_t *)val) = (dev->connected) ? NETOPT_ENABLE
+                                                         : NETOPT_DISABLE;
+            return 1;
         default:
             return netdev_eth_get(netdev, opt, val, max_len);
     }

cpu/esp32/esp-wifi/esp_wifi_netdev.h

@@ -11,7 +11,7 @@
  * @{
  *
  * @file
- * @brief       Netdev interface for the ESP WiFi AP-based communication
+ * @brief       Network device driver for the ESP32 WiFi interface
  *
  * @author      Gunar Schorcht <gunar@schorcht.net>
  */
@@ -37,10 +37,10 @@ typedef struct
 {
     netdev_t netdev;                   /**< netdev parent struct */
 
-    uint8_t rx_len;                    /**< number of bytes received */
+    uint16_t rx_len;                   /**< number of bytes received */
     uint8_t rx_buf[ETHERNET_DATA_LEN]; /**< receive buffer */
 
-    uint8_t tx_len;                    /**< number of bytes in transmit buffer */
+    uint16_t tx_len;                   /**< number of bytes in transmit buffer */
     uint8_t tx_buf[ETHERNET_DATA_LEN]; /**< transmit buffer */
 
     uint32_t event;                    /**< received event */

cpu/esp32/esp-wifi/esp_wifi_params.h

@@ -8,10 +8,11 @@
 
 /**
  * @ingroup     cpu_esp32_esp_wifi
+ * @ingroup     cpu_esp32_conf
  * @{
  *
  * @file
- * @brief       Parameters for the netdev interface for ESP WiFi module
+ * @brief       Parameters for the ESP32 WiFi netdev interface
  *
  * @author      Gunar Schorcht <gunar@schorcht.net>
  */
@@ -25,14 +26,33 @@
  * @name    Set default configuration parameters for the ESP WiFi netdev driver
  * @{
  */
+
+/**
+ * @brief   The size of the stack used for the ESP WIFI netdev driver thread.
+ */
 #ifndef ESP_WIFI_STACKSIZE
-/** The size of the stack used for the ESP WiFi netdev driver thread */
-#define ESP_WIFI_STACKSIZE    THREAD_STACKSIZE_DEFAULT
+#define ESP_WIFI_STACKSIZE  (THREAD_STACKSIZE_DEFAULT)
 #endif
 
+/**
+ * @brief   The priority of the ESP WiFi netdev driver thread. Should not be changed.
+ */
 #ifndef ESP_WIFI_PRIO
-/** The priority of the ESP WiFi netdev driver thread */
-#define ESP_WIFI_PRIO         GNRC_NETIF_PRIO
+#define ESP_WIFI_PRIO       (GNRC_NETIF_PRIO)
+#endif
+
+/**
+ * @brief   SSID of the AP to be used.
+ */
+#ifndef ESP_WIFI_SSID
+#define ESP_WIFI_SSID       "RIOT_AP"
+#endif
+
+/**
+ * @brief   Passphrase used for the AP as clear text (max. 64 chars).
+ */
+#ifndef ESP_WIFI_PASS
+#define ESP_WIFI_PASS       "ThisistheRIOTporttoESP"
 #endif
 
 /**@}*/

cpu/esp_common/esp-now/doc.txt

@@ -26,17 +26,22 @@ USEMODULE += esp_now
 
 For ESP-NOW, ESP32 nodes are used in WiFi SoftAP + Station mode to advertise their SSID and become visible to other ESP32 nodes. The SSID of an ESP32 node is the concatenation of the prefix ```RIOT_ESP_``` with the MAC address of its SoftAP WiFi interface. The driver periodically scans all visible ESP32 nodes.
 
-The following parameters are defined for ESP-NOW nodes. These parameters can be overriden by [application-specific board configurations](#esp32_application_specific_board_configuration).
+The following parameters are defined for ESP-NOW nodes.
 
 <center>
 
 Parameter | Default | Description
 :---------|:--------|:-----------
 ESP_NOW_SCAN_PERIOD | 10000000UL | Defines the period in us at which an node scans for other nodes in its range. The default period is 10 s.
-ESP_NOW_SOFT_AP_PASSPHRASE | ThisistheRIOTporttoESP | Defines the passphrase (max. 64 chars) that is used for the SoftAP interface of an nodes. It has to be same for all nodes in one network.
+ESP_NOW_SOFT_AP_PASS | "ThisistheRIOTporttoESP" | Defines the passphrase as clear text (max. 64 chars) that is used for the SoftAP interface of ESP-NOW nodes. It has to be same for all nodes in one network.
 ESP_NOW_CHANNEL | 6 | Defines the channel that is used as the broadcast medium by all nodes together.
 ESP_NOW_KEY | NULL | Defines a key that is used for encrypted communication between nodes. If it is NULL, encryption is disabled. The key has to be of type ```uint8_t[16]``` and has to be exactly 16 bytes long.
 
 </center>
 
+@note The ESP-NOW network interface (module `esp_now`) and the
+Wifi network interface (module `esp_wifi`)
+can be used simultaneously, for example, to realize a border router for
+a mesh network which uses ESP-NOW.
+
  */