UDP Joystick Control

This project uses an ESP32 to read the Joystick Control data sent via UDP. The system identifies the device using mDNS, starts a UDP Server, and receive the joystick control frames.

Code Explanation

Libraries Used

• Async UDP: Provides asynchronous UDP support, this process runs on Core 1 of ESP32 in parallel with Core 0 so this is non-blocking in nature.
• ESPmDNS: For mDNS discovery to find the IP address of the transmitting device on the local network.
• HttpClient: For making HTTP request to the transmitting device to start or stop the joystick service.
• WiFi: To connect ESP32 to local WiFi network
• FreeRTOS: For managing queues,i.e., transferring data from Core 1 to Core 0

Important

• ESP32 has 2 cores Core 0 and Core 1, Core 0 runs the code in the setup() and loop() functions, Core 1 is dedicated for Networking related Tasks, like Wifi and Bluetooth Callbacks.
• There should be minimum processing in the Core 1 and it should be only used to receive the data and then sent it to Core 0 for further processing.
• For sending data form Core 1 to Core 0 one should never use direct variables addressing as the two cores run asynchronously and this can result in random bits flipping. To send data between core one must use queues.

Functions Used

• startWiFi(): Initializes the WiFi connection.
• startmDNS(): Sets up mDNS to discover the device and find its IP and port.
• startJoystick(IP): Asks the Joystick Device to begin communication.
• startAsyncUDPServer(port): Starts listening on the UDP port.

Code Walkthrough

1. Setup

   • The Serial connection starts at 115200 baud for debugging.
   • A FreeRTOS queue udpQueue is created to handle incoming UDP joystick packets (pkt).
   • WiFi and mDNS are started using the startWiFi() and startmDNS() functions.
   • The joystick control service begins using startJoystick() with the IP found through mDNS.
   • The UDP server starts with startAsyncUDPServer() on the port obtained from mDNS.

2. Loop

   • Inside the loop(), the code waits to receive packets from the UDP queue using xQueueReceive().
   • When a packet arrives, the channel data is read from and copied to a struct called Packet.

For more details, you can refer to:

• The ExpressLRS pull request that inspired this implementation: ExpressLRS/ExpressLRS#2444
• Espresiff documentation, on how to use queues and FreeRTOS.
• This article on UDP Protocol