Add docs for espnow

README.md

@@ -21,7 +21,7 @@
 * Dedicated for education and research.
 * Made from general-purpose components.
 * Simple and clean source code in Arduino (<2k lines firmware).
-* Connectivity using Wi-Fi and MAVLink protocol.
+* Communication with MAVLink protocol using Wi-Fi or ESP-NOW.
 * Control using USB gamepad, remote control or smartphone.
 * Wireless command line interface and analyzing.
 * Precise simulation with Gazebo.

docs/usage.md

@@ -290,11 +290,8 @@ The Wi-Fi mode is chosen using `WIFI_MODE` parameter in QGroundControl or in the
 
 * `0` — Wi-Fi is disabled.
 * `1` — Access Point mode *(AP)* — the drone creates a Wi-Fi network.
-* `2` — Client mode *(STA)* — the drone connects to an existing Wi-Fi network.
+* `2` — Client mode *(STA)* — the drone connects to an existing Wi-Fi network (may cause additional delays, so generally not recommended).
-* `3` — *ESP-NOW (not implemented yet)*.
+* `3` — ESP-NOW mode — the drone uses ESP-NOW protocol for communication.
-
-> [!WARNING]
-> Tests showed that Client mode may cause **additional delays** in remote control (due to retranslations), so it's generally not recommended.
 
 The SSID and password are configured using the `ap` and `sta` console commands:
 
@@ -316,6 +313,37 @@ Disabling Wi-Fi:
 p WIFI_MODE 0
 ```
 
+### Using ESP-NOW
+
+[ESP-NOW](https://docs.espressif.com/projects/esp-idf/en/stable/esp32/api-reference/network/esp_now.html) is a low level wireless communication protocol. It can provide lower latency, better reliability, and longer range than Wi-Fi. However, it requires a second ESP32 board to be used as a proxy for the computer.
+
+<img src="img/espnow-connection.jpg" width="600">
+
+To setup ESP-NOW communication:
+
+1. Flash the second ESP32 board with ESP-NOW proxy sketch: [`tools/espnow-proxy/espnow-proxy.ino`](../tools/espnow-proxy/espnow-proxy.ino). Use Arduino IDE or command line: `make upload_proxy`.
+
+2. Open Serial Monitor or use `make monitor` command. The ESP32 will print its MAC address and generated encryption key, for example:
+
+   ```
+   espnow 7a:c8:e3:eb:bf:e9 &PiuSysxP9+$L&5E
+   ```
+
+   Run this line as a console command on each drone you want to bind to this proxy board.
+
+3. Set the `WIFI_MODE` parameter to `3` on the drone:
+
+   ```
+   p WIFI_MODE 3
+   ```
+
+4. Go to the QGroundControl menu ⇒ *Application Settings* ⇒ *Comm Links*, add new link with the following settings:
+   * Name: ESP32.
+   * Type: Serial.
+   * Serial Port: choose the port of the proxy ESP32 board, e. g. `/dev/cu.usbserial-0001`.
+   * Baud Rate: 115200.
+5. Click *Save*. QGroundControl should connect to the drone using ESP-NOW and begin showing the telemetry.
+
 ## Flight log
 
 After the flight, you can download the flight log for analysis wirelessly. Use the following command on your computer for that:

tools/espnow-proxy/espnow-proxy.ino

@@ -3,13 +3,13 @@
 
 // Proxy for ESP-NOW connection
 
+#include <vector>
 #include <WiFi.h>
 #include <ESP32_NOW_Serial.h>
 #include <MacAddress.h>
 #include <MAVLink.h>
 #include <Preferences.h>
 #include "../../flix/util.h"
-#include <vector>
 
 const int CHANNEL = 6;
 char key[ESP_NOW_KEY_LEN + 1] = {0}; // with trailing null
@@ -61,7 +61,7 @@ void generateRandomKey() {
 void loop() {
 	uint8_t buf[5000];
 
-	// Send from serial to ESP-NOW
+	// Send from Serial to ESP-NOW
 	while (Serial.available() > 0) {
 		int b = Serial.read();
 		if (b < 0) {
@@ -78,7 +78,7 @@ void loop() {
 		}
 	}
 
-	// Send from ESP-NOW to serial
+	// Send from ESP-NOW to Serial
 	for (ESPNOWSerial *link : peers) {
 		int len = link->read(buf, sizeof(buf));
 		if (len > 0) {