Adding a User Application to NuttX
Tuesday, June 6th, 2023
So far we have seen how to deploy NuttX to a Raspberry Pi PicoW and enable C++ in NuttX. Next up we will create our own application and deploy it to the PicoW.
Creating a New Application
The build system for NuttX applications uses a a makefile that is written in such a way that all we have to do to add a new application is simply create a directory containing some template files. The easiest way to do this is to use an existing application as a template. So let us start by making a copy of the helloxx application. This can be found in the apps repository in the examples directory. So we will start by making a recursive copy of this directory and renaming it ssem.
Looking inside the ssem directory we find a number of files:
helloxx_main.cxx Make.defs Kconfig Makefile
Time to start editing the files.
helloxx_main.cxx
We will start by renaming the file to represent the application name, so we will rename this to ssem_main.cxx. Now editing the file we change all occurrences of helloxx_main to ssem_main. This will allow us to verify that we have indeed deployed the application.
Makefile
Make a similar change to the Makefile by changing all occurrences of helloxx to ssem. Make changes to the comments to reflect that this application is a new application. Our Makefile should now look something like this:
include $(APPDIR)/Make.defs # SSEM Application MAINSRC = ssem_main.cxx # ssem built-in application info PROGNAME = ssem PRIORITY = SCHED_PRIORITY_DEFAULT STACKSIZE = $(CONFIG_DEFAULT_TASK_STACKSIZE) MODULE = $(CONFIG_EXAMPLES_SSEM) include $(APPDIR)/Application.mk
Make.defs
The Make.defs file conditionally adds the new application to the list of configured applications and ensures that the file will be built. This file should be edited to look something like this:
ifneq ($(CONFIG_EXAMPLES_SSEM),) CONFIGURED_APPS += $(APPDIR)/examples/ssem endif
Kconfig
The Kconfig file allows us to define and change application parameters, something we may look at later. For the moment it simply defines the application name and title and tells the configuration system how to turn compilation on or off. Making changes similar to the above we will have a file that contains something like this:
config EXAMPLES_SSEM
tristate "SSEM example"
default n
depends on HAVE_CXX
---help---
Enable the SSEM application
Build the SSEM Application
Now we have set up the application we can start to reconfigure the build system and deploy the application. First thing to do is to clean the current build environment in order to make NuttX aware of the presence of the application. Issuing the command make clean will remove the previous build components.
Now we can configure the environment by issuing the make menuconfig command. This will present the configuration menuing system we saw in the previous post. So now head over to the following menu items and disable the Hello, world example and enable the SSEM example.
- Main menu -> Application Configuration -> “Hello, World!” C++ example
- Main menu -> Application Configuration -> SSEM example
We should now be ready to build the system, so execute the command make -j to build the system. The build system should show output similar to the following if the changes to the system have been made correctly:
Create version.h LN: platform/board to /Projects/NuttX/apps/platform/dummy Register: ssem Register: nsh Register: sh CPP: /Projects/NuttX/nuttx/boards/arm/rp2040/raspberrypi-pico-w/scripts/raspberrypi-pico-flash.ld-> /Projects/NuttX/nuttx/boards/arm/rp2040/raspberrypi-pico-w/scripts/raspberrypi-pico-flash.lLD: nuttx Generating: nuttx.uf2 tools/rp2040/elf2uf2 nuttx nuttx.uf2;
Time to deploy NuttX to the board and check to see if the application has built correctly. So copy the NuttX.uf2 file to the board and connect a serial console to the serial port. Press enter a few times until the nsh prompt appears and now type help. The new application should appear in the list of built in applications:
Builtin Apps:
nsh sh ssem
Executing the ssem application should now present something similar to the following (depending upon how you modified the helloxx_main application code):
nsh> ssem
ssem_main: Saying hello from the dynamically constructed instance
CHelloWorld::HelloWorld: Hello, World!!
ssem_main: Saying hello from the instance constructed on the stack
CHelloWorld::HelloWorld: Hello, World!!
nsh>
Conclusion
The process of creating a new application and having this included in the NuttX build system is not a difficult task, it simply means editing a few files.
One key step is the make clean step as omitting this from a system which already contains build artefacts may not include the new application in the configuration process and hence exclude the files from the build.
In the next post we will add SMP to the configuration.
