NodeMCU is an open source Lua based firmware for the ESP8266 WiFi SOC from Espressif and uses an on-module flash-based SPIFFS file system. NodeMCU is implemented in C and is layered on the Espressif NON-OS SDK.
The firmware was initially developed as is a companion project to the popular ESP8266-based NodeMCU development modules, but the project is now community-supported, and the firmware can now be run on any ESP module.
The NodeMCU programming model is similar to that of Node.js, only in Lua. It is asynchronous and event-driven. Many functions, therefore, have parameters for callback functions. To give you an idea what a NodeMCU program looks like study the short snippets below. For more extensive examples have a look at the /lua_examples
folder in the repository on GitHub.
-- a simple HTTP server
srv = net.createServer(net.TCP)
srv:listen(80, function(conn)
conn:on("receive", function(sck, payload)
print(payload)
sck:send("HTTP/1.0 200 OK\r\nContent-Type: text/html\r\n\r\n<h1> Hello, NodeMCU.</h1>")
end)
conn:on("sent", function(sck) sck:close() end)
end)
-- connect to WiFi access point
wifi.setmode(wifi.STATION)
wifi.sta.config("SSID", "password")
-- register event callbacks for WiFi events
wifi.sta.eventMonReg(wifi.STA_CONNECTING, function(previous_state)
if(previous_state==wifi.STA_GOTIP) then
print("Station lost connection with access point. Attempting to reconnect...")
else
print("STATION_CONNECTING")
end
end)
-- manipulate hardware like with Arduino
pin = 1
gpio.mode(pin, gpio.OUTPUT)
gpio.write(pin, gpio.HIGH)
print(gpio.read(pin))
In July 2018 support for a Lua Flash Store (LFS) was introduced. LFS allows Lua code and its associated constant data to be executed directly out of flash-memory; just as the firmware itself is executed. This now enables NodeMCU developers to create Lua applications with up to 256Kb Lua code and read-only constants executing out of flash. All of the RAM is available for read-write data!