ESP8266 MicroPython Automatically Remembers WiFi

There were a few speed bumps on my way to a MicroPython interactive prompt, also known as REPL the read, evaluate, print loop. But once I got there, I was pretty impressed. It was much friendlier to iterative experimentation than Arduino on an ESP8266, because I don’t have to reflash and reboot every time. And since the ESP8266 has WiFi capabilities, getting REPL over the network (WebREPL) is even cooler. Now I can experiment while it runs on another power source, completely independent of USB for either power of data.

Before I got there, though, I needed to get this ESP8266 on my home WiFi network. By default, MicroPython sets up an access point for its own network so I need to turn “AP mode” off. Then I turn on “station mode” which allows connection to my WiFi router given its SSID and password.

import network

ap = network.WLAN(network.AP_IF)

sta = network.WLAN(network.STA_IF)
sta.config(dhcp_hostname='my hostname')
sta.connect('my wifi ssid','my wifi password')

I added one optional element: the dhcp_hostname parameter. This is the name shown to my router and probably other devices on my home network. If I don’t set this, the default name is “ESP-” followed by six hexadecimal digits of the ESP8266’s MAC address. That’s not a particularly memorable name so I wanted something I could remember and recognize.

And then, to my surprise, MicroPython remembered the network settings upon restart. I wrote a piece of Python code to perform this routine that I could run whenever I rebooted the board. But when I set out to test it by rebooting the board, it automatically reconnected to WiFi. This tells me a successful WiFi connection would cause a write to flash memory, which implies I should not run my WiFi connection code upon every startup. I expect to make this board go to deep sleep frequently and, if it writes WiFi information to flash every time it wakes up, I will quickly wear out the flash.

But that is just a hypothesis. As MicroPython is an open source project, it should be possible for me to dig into the code and figure out exactly when MicroPython writes WiFi connection information to flash. Perhaps it isn’t as bad as I feared it would be. Until then, however, I will hold off running my WiFi connection script.

A downside of not running my script is the DHCP hostname, which is not remembered upon reboot and this board reverted back to the default ESP-prefix name. But I can live with that for now, the next step is to set up my hardware for playing with deep sleep under battery power.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s