NodeMCU is an eLua based firmware for the ESP8266 WiFi SOC from Espressif. The firmware is based on the Espressif NON-OS SDK 1.5.1 and uses a file system based on spiffs. The code repository consists of 98.1% C-code that glues the thin Lua veneer to the SDK.

The NodeMCU firmware is a companion project to the popular NodeMCU dev kits, ready-made open source development boards with ESP8266-12E chips.

• Easy to program wireless node and/or access point
• Based on Lua 5.1.4 (without debug, os modules)
• Asynchronous event-driven programming model
• 35+ built-in modules
• Firmware available with or without floating point support (integer-only uses less memory)
• Up-to-date documentation at https://nodemcu.readthedocs.org

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(conn, payload)
		print(payload)
		conn:send("<h1> Hello, NodeMCU.</h1>")
	end)
	conn:on("sent", function(conn) conn:close() end)
end)

-- connect to WiFi access point
wifi.setmode(wifi.STATION)
wifi.sta.config("SSID", "password")

The entire NodeMCU documentation is maintained right in this repository at /docs. The fact that the API documentation is mainted in the same repository as the code that provides the API ensures consistency between the two. With every commit the documentation is rebuilt by Read the Docs and thus transformed from terse Markdown into a nicely browsable HTML site at https://nodemcu.readthedocs.org.

• How to build the firmware
• How to flash the firmware
• How to upload code and NodeMCU IDEs
• API documentation for every module

See https://nodemcu.readthedocs.org/en/dev/en/support/.

MIT © zeroday/nodemcu.com

The following sections explain some of the options you have if you want to build your own NodeMCU firmware.

Disable modules you won't be using to reduce firmware size and free up some RAM. The ESP8266 is quite limited in available RAM and running out of memory can cause a system panic.

Edit app/include/user_modules.h and comment-out the #define statement for modules you don't need. Example:

...
#define LUA_USE_MODULES_MQTT
// #define LUA_USE_MODULES_COAP
// #define LUA_USE_MODULES_U8G
...

Identify your firmware builds by editing app/include/user_version.h

#define NODE_VERSION    "NodeMCU 1.5.1+myname"
#ifndef BUILD_DATE
#define BUILD_DATE      "YYYYMMDD"
#endif

The initial baud rate at boot time is 9600bps. You can change this by editing BIT_RATE_DEFAULT in app/include/user_config.h:

#define BIT_RATE_DEFAULT BIT_RATE_115200

To enable runtime debug messages to serial console edit app/include/user_config.h

#define DEVELOP_VERSION

DEVELOP_VERSION changes the startup baud rate to 74880bps.