Day: July 10, 2018

Running external application on NuttX

Normally NuttX supports internal (Built-In) applications embedded on its firmware. When you run: “nsh> hello” or your application, NuttX look for the application inside the internal flash of the microcontroller and run it.

But NuttX also supports running external applications. These external applications are ELF files. The ELF format is the default executable format used on Linux and almost all Unix OS.

Normally the OS needs to create a Global Symbol Table (AKA: symtab) where the ELF look at to translate the used functions of the ELF binary to memory addresses where these functions exist in the OS.

The “drawback” of this symtab is because it will waste a lot of space inside the flash (firmware) of the OS.

Fortunately NuttX also supports an alternative solution where this symtab is not needed. The ELF binary is created with the fixed memory position of each function address position. The drawback of this solution is the ELF binary is not relocatable, in other words: if you compile a new firmware for your board the existent external ELF binary could to fail because these functions positions are located at a different position now.

You can find the instructions for both options here:

http://www.nuttx.org/doku.php?id=wiki:nshhowtos:elf-addon

I tested the “no-symtab” option loading an external “hello” from a USB Flash Drive:

NuttShell (NSH)
nsh> ls /dev
/dev:
 console
 null
 sda
 ttyS0
nsh> ?
help usage:  help [-v] []

  [           dirname     help        mh          set         unset       
  ?           dd          hexdump     mount       sh          usleep      
  basename    df          kill        mv          sleep       xd          
  break       echo        ls          mw          test        
  cat         exec        mb          ps          time        
  cd          exit        mkdir       pwd         true        
  cp          false       mkfatfs     rm          uname       
  cmp         free        mkrd        rmdir       umount      

Builtin Apps:
  hello
nsh> hello
Hello, World!!

nsh> mount -t vfat /dev/sda /bin
nsh> hello
Hello world from external binary!
nsh>

As you can see initially the internal “hello” program was executed, but after I mounted the USB Flash Drive to /bin the external “hello” takes precedence over the internal.

These are the options I need to get it working:

CONFIG_STM32_OTGFS=y
CONFIG_STM32_CCMEXCLUDE=y
CONFIG_SCHED_WORKQUEUE=y
CONFIG_SCHED_HPWORK=y
CONFIG_USBHOST=y
CONFIG_USBHOST_ISOC_DISABLE=y
CONFIG_USBHOST_MSC=y
CONFIG_FS_FAT=y
CONFIG_BINFMT_EXEPATH=y
CONFIG_PATH_INITIAL="/bin"
CONFIG_ELF=y
CONFIG_LIBC_ARCH_ELF=y
CONFIG_LIBC_EXECFUNCS=y
# CONFIG_EXECFUNCS_HAVE_SYMTAB is not set
CONFIG_EXAMPLES_HELLO=y
CONFIG_NSH_FILE_APPS=y
CONFIG_NSH_ARCHINIT=y