Steps to configure NuttX to run a built-in app from NuttX Command Line (Nutt SHell or NSH)

For people who are new to NuttX like me, in a sentence, NuttX is an embedded RTOS. You can read the overview at nuttx.org. If you have tried building NuttX for your favorite board with the example application or your own application, you may be looking to run your application concurrently from NSH (Nutt SHell) as like we do in GNU/Linux Command line. Bringing up such feature is by enabling Built-In application. The following explanation is a digest of my learning from 'NuttX/apps/README.txt' and acassis blog post.

1. To enable built-in app to be available in nsh, edit 'nuttx/configs/<board_name>/nsh/defconfig' and add the below configurations
   

   CONFIG_BUILTIN=y
   CONFIG_NSH_BUILTIN_APPS=y
   
   CONFIG_EXAMPLES_MYAPP=y /* To allow configuring myapp as
                              built-in app */

2. fork 'apps/examples/hello' to 'apps/examples/myapp' and
   
   
   1. rename 'myapp/hello_main.c' to 'myapp/myapp.c'
       
      
   2. Edit 'myapp/mayapp.c' and change 'hello_main()' to 'myapp_main()'
       
      
   3. modify 'myapp/Kconfig' to resemble the following code to reflect your application name
      
      

      config EXAMPLES_MYAPP
              bool "\"Myapp Hello, World!\" example"
              default n
              ---help---
                      Enable the \"Myapp Hello, World!\" example
      
      if EXAMPLES_MYAPP
      
      config EXAMPLES_MYAPP_PROGNAME
              string "Myapp Program name"
              default "myapp"
              depends on BUILD_KERNEL
              ---help---
                      This is the name of the program that will be
                      use when the NSH ELF program is installed.
      
      endif

   4. modify 'myapp/Makefile' with the following to reflect your application name.
      
      

      APPNAME         = myapp
      CSRCS           = myapp.c

      
      Note: The 'APPNAME' above should reflect the prefix in myapp_main() and this is the same name by which your NSH command line app will be.
   5. modify 'myapp/Make.defs' to reflect the following code
      
      

      ifeq ($(CONFIG_EXAMPLES_MYAPP),y)
              CONFIGURED_APPS += examples/myapp
      endif

      • check 'apps/examples/Make.defs' for
        
        

        include $(wildcard examples/*/Make.defs)

        if its not present, add it. This makes 'Make.defs' file in every examples subdirectory to be added when configuring. (In otherways, the 'myapp/Make.defs' can be omitted and its contents can be copied to this 'Make.defs' file.)
3. In 'apps/examples/Kconfig' file, include
   
   

   source "$APPSDIR/examples/myapp/Kconfig"

4. fork 'nuttx/configs/hello' to 'nuttx/configs/myapp' and modify 'myapp/defconfig' to add
   
   

   CONFIG_EXAMPLES_MYAPP=y

   and comment all other examples if enabled. Say,

   # CONFIG_EXAMPLES_HELLO is not set

5. At this point, everything is set and ready if you are not using any hardware peripheral such as UART, SPI, I2C, CAN, etc. You can jump to the next step. If you are accessing any hardware peripheral, then you need to set the corresponding configuration macros as true. You can do that in 'nuttx/config/<board_name>/myapp/defconfig'
    
   
6. In terminal, go to 'nuttx/tools' and run the following command to tell the Makefile to use 'nsh' example.
   
   

   $ ./configure.sh <board_name>/nsh

7. Switch back to 'nuttx' directory and run 'make' but with the parameters as below to choose the required toolchain.
   
   

   $ make CONFIG_ARMV7M_TOOLCHAIN_CODESOURCERYL=y
          CONFIG_ARMV7M_TOOLCHAIN_BUILDROOT=n 

After building and dumping the code, in nsh, using the command 'help'will list the available built-in app by the name as you provided for the 'APPNAME' macro in the Makefile.