NuttX RTOS

What is NuttX?

NuttX is a mature and secure real-time operating system (RTOS) with an emphasis on technical standards compliance and small size. It is scalable from 8-bit to 64-bit microcontrollers and microprocessors and compliant with the Portable Operating System Interface (POSIX) and the American National Standards Institute (ANSI) standards and with many Linux-like subsystems. The best way to think about NuttX is to think of it as a small Unix/Linux for microcontrollers.

Highlights of NuttX

Small - Fits and runs in microcontrollers as small as 32 kB Flash and 8 kB of RAM.
Compliant - Strives to be as compatible as possible with POSIX and Linux.
Versatile - Supports many architectures (ARM, ARM Thumb, AVR, MIPS, OpenRISC, RISC-V 32-bit and 64-bit, RX65N, x86-64, Xtensa, Z80/Z180, etc.).
Modular - Its modular design allows developers to select only what really matters and use modules to include new features.
Popular - NuttX is used by many companies around the world. Probably you already used a product with NuttX without knowing it was running NuttX.
Predictable - NuttX is a preemptible Realtime kernel, so you can use it to create predictable applications for realtime control.

Why NuttX + LVGL?

Although NuttX has its own graphic library called NX, LVGL is a good alternative because users could find more eye-candy demos and they can reuse code from previous projects. LVGL is an Object-Oriented Component Based high-level GUI library, that could fit very well for a RTOS with advanced features like NuttX. LVGL is implemented in C and its APIs are in C.

Here are some advantages of using LVGL in NuttX

Develop GUI in Linux first and when it is done just compile it for NuttX. Nothing more, no wasting of time.
Usually, GUI development for low level RTOS requires multiple iterations to get things right, where each iteration consists of Change code > Build > Flash > Run. Using LVGL, Linux and NuttX you can reduce this process and just test everything on your computer and when it is done, compile it on NuttX and that is it.

NuttX + LVGL could be used for

GUI demos to demonstrate your board graphics capacities.
Fast prototyping GUI for MVP (Minimum Viable Product) presentation.
visualize sensor data directly and easily on the board without using a computer.
Final products with a GUI without a touchscreen (i.e. 3D Printer Interface using Rotary Encoder to Input data).
Final products with a touchscreen (and all sorts of bells and whistles).

How to get started with NuttX and LVGL?

There are many boards in the NuttX mainline with support for LVGL. Let's use the STM32F429IDISCOVERY as an example because it is a very popular board.

First you need to install the pre-requisites on your system

Let's use the Windows Subsystem for Linux

$ sudo apt-get install automake bison build-essential flex gcc-arm-none-eabi gperf git libncurses5-dev libtool libusb-dev libusb-1.0.0-dev pkg-config kconfig-frontends openocd

Now let's create a workspace to save our files

$ mkdir ~/nuttxspace
$ cd ~/nuttxspace

Clone the NuttX and Apps repositories:

$ git clone https://github.com/apache/incubator-nuttx nuttx
$ git clone https://github.com/apache/incubator-nuttx-apps apps

Configure NuttX to use the stm32f429i-disco board and the LVGL Demo

$ ./tools/configure.sh stm32f429i-disco:lvgl
$ make

If everything went fine you should have now the file nuttx.bin to flash on your board:

$ ls -l nuttx.bin
-rwxrwxr-x 1 alan alan 287144 Jun 27 09:26 nuttx.bin

Flashing the firmware in the board using OpenOCD:

$ sudo openocd -f interface/stlink-v2.cfg -f target/stm32f4x.cfg -c init -c "reset halt" -c "flash write_image erase nuttx.bin 0x08000000"

Reset the board and using the 'NSH>' terminal start the LVGL demo:

nsh> lvgldemo

Where can I find more information?

This blog post: LVGL on LPCXpresso54628
NuttX mailing list: Apache NuttX Mailing List

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