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
NuttX Simulator
The NuttX simulator allows you to run NuttX and LVGL on your PC. This can be especially useful for developing LVGL UIs with immediate visual feedback, and also developing platform independent NuttX apps.
Configure NuttX to use the sim
board and the LVGL Demo
$ ./tools/configure.sh sim:lvgl_fb
$ make
If everything went fine you should have now the file nuttx
$ ls -l nuttx
-rwxr-xr-x 1 root root 2819920 May 12 15:01 nuttx
Running the NuttX Simulator
$ ./nuttx
Using the 'NSH>' terminal start the LVGL demo:
nsh> lvgldemo
NuttX On-Device
If you don't have an STM32F429I-DISCO, this process will be similar for other boards.
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
Custom Usage
The example app called lvgldemo
uses LVGL's NuttX integration
to run the demos in NuttX.
https://github.com/apache/nuttx-apps/tree/master/examples/lvgldemo
It is used by all LVGL defconfigs. See sim:lvgl_fb
and sim:lvgl_lcd
.
You can use it as a reference for adding LVGL to your own NuttX app.
Start by copying the contents of lvgldemo.c
. It handles fb and lcd based
display drivers, the touchscreen input driver, and libuv.
NuttX Driver Support
fbdev - LVGL can create a display for
/dev/fb*
devices.lcd - LVGL can create a display for
/dev/lcd*
devices.input/uinput touchscreen - LVGL can create an indev(s) for touch devices that use the NuttX input/uinput system.
libuv - LVGL has support for using libuv as its event loop manager. libuv apps can integrate seamlessly.
There is no support for input/uinput keyboards yet. The NuttX X11 sim keyboard driver emits keycodes that are not standard so the LVGL integration with it would not be generic, if it were added.
Other Integrations
LVGL+NuttX profiler integration
Optional dedicated image cache heap
Configurations
The LVGL library is a NuttX "app". You can configure LVGL in menuconfig
.
$ ./tools/configure.sh stm32f429i-disco:lvgl
$ make menuconfig
The LVGL Kconfig
file provides the available config options to the NuttX build system. The LVGL configs in
menuconfig
can be found under
Application Configuration > Graphics Support > Light and Versatile Graphic Library (LVGL) > LVGL configuration.
To find the location of a specific config, Press the "/" key to open a search interface.
Here are some configurations that you can use to customize your NuttX and LVGL setup:
LV_USE_NUTTX_INDEPENDENT_IMAGE_HEAP - You can enable or disable the LVGL image heap in NuttX. By default, it is disabled. If you enable it, LVGL will use the NuttX heap instead.
Using LV_STDLIB_CLIB
for LV_USE_STDLIB_MALLOC
,
LV_USE_STDLIB_STRING
, or LV_USE_STDLIB_SPRINTF
is
reasonable as NuttX fully implements these standard library APIs. Whether or
not you choose to use NuttX's malloc
depends on whether you want LVGL
to allocate from the NuttX global heap or use its own.
Where is LV_OS_NUTTX
?
NuttX tries to be POSIX compliant where possible, meaning it supports
pthreads (POSIX threads). To enable OS features in LVGL on NuttX,
set LV_USE_OS
to LV_OS_PTHREAD
.
The main reason for enabling OS features is for multi-core rendering.
See LV_DRAW_SW_DRAW_UNIT_CNT
. Otherwise there is no case
for setting it.
Using a Specific Version of LVGL
Here are the steps to use the latest (or any) version of LVGL in NuttX.
First ensure the build artifacts have been cleared. It will remove the existing unpacked LVGL and ZIP if there is one.
$ make distclean
Now you can git clone
the latest LVGL into the NuttX apps tree. It will persist even after make distclean
because the build system will not remove lvgl if it is a Git repo.
$ cd /path/to/nuttxspace/apps/graphics/lvgl
$ git clone https://github.com/lvgl/lvgl.git
Finally, you must copy the content of apps/graphics/lvgl/lvgl/Kconfig
into
the middle of apps/graphics/lvgl/Kconfig
. See the "PASTE THE CONTENTS ..." section below.
apps/graphics/lvgl/Kconfig
:
#
# For a description of the syntax of this configuration file,
# see the file kconfig-language.txt in the NuttX tools repository.
#
menuconfig GRAPHICS_LVGL
bool "Light and Versatile Graphic Library (LVGL)"
default n
---help---
Enable support for the LVGL GUI library.
if GRAPHICS_LVGL
(PASTE THE CONTENTS OF apps/graphics/lvgl/lvgl/Kconfig HERE)
config LV_OPTLEVEL
string "Customize compilation optimization level"
default ""
endif # GRAPHICS_LVGL
Where can I find more information?
This blog post: LVGL on LPCXpresso54628
NuttX mailing list: Apache NuttX Mailing List