Notes On Getting ESP32 On WiFi

I’m working towards a minimal first draft of my Sawppy rover’s HTML-based control scheme. I tackled client side first because that side had more similarity to my earlier SGVHAK rover control project. I got a first draft by using a Node.js server on my desktop as a placeholder for the ESP32, now it’s time to start working on the real server code. The first step is to learn how to activate an ESP32’s WiFi capabilities in software.

There are many options on how to set up networking between an ESP32 and a browser running on a phone. I decided to start with connecting it as a node to my home network, which Espressif documentation calls “station mode“. I expect this to be easier to develop and debug, but obviously it won’t work for a rover roaming away from home. For that the ESP32 will have to be switched to “AP mode” acting as a WiFi access point. In order to accommodate this, I aim to structure my code so setting up a WiFi connection is its own separate FreeRTOS task, so that I can switch between station and AP (or maybe even more?) variants as needed at compile-time. If I ever need the option to switch between modes at runtime, I can integrate one of the available ESP32 WiFi managers.

To learn about setting up an ESP32 in station mode, Espressif’s written documentation is pretty thin. I had to do most of my learning from their station example, and thankfully it was indeed enough to get my ESP32 on my network. Converting the sample code to a FreeRTOS task I can incorporate into my rover project required more than 2 kilobyte of stack, which is what I had been using as a default. A bit of quick experimentation established 3 kilobytes are enough for the new WiFi task. Right now I’m not too worried about RAM footprint, so I won’t spend time pinning down exactly where between 2 and 3 it needs.

One item that I saw and copied without understanding, was a code block initializing an ESP32’s non-volatile storage (NVS) used to store information in key-value pairs. I can infer that ESP32 WiFi stack required some of those values, but I couldn’t find documentation on exactly what was needed. The more obvious WiFi-related pieces of information (like the SSID for my home network and associated password) are in my code, so it must be something less obvious but I don’t yet know what they are.

Events were an aspect of the sample code that confused me for a while. Eventually I figured out my confusion stemmed from the fact I got two items mixed up. One of them is an “Event Group“, which is a FreeRTOS mechanism used here so a piece of code could wait until WiFi initialization completes before they start doing network things. The other mechanism is an “Event Loop” which is an Espressif creation for ESP-IDF. They both had “event” in their name but were completely independent, which was why I got lost trying to understand how the two mechanisms interacted behind the scenes: the answer is that they don’t! So when reading the code it’s important to figure out which “event” we are talking about. The Espressif reference for WiFi initialization events, for example, refers to the event loop.

I’m happy I was successful in connecting an ESP32 to my home WiFi by following example code. Now that it is on the network, I need to make it do something useful.

[Code for this project is publicly available on GitHub.]

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