NuttX, Getting Started

NuttX is a small footprint Real-Time Operating System (RTOS) for microcontroller environments. NuttX provides a POSIX API, with a single process, multi-threaded environment. NuttX has been ported to various architecture including ARM, AVR, AVR32 and Zilog.

In this article, we will explore the file system, storage and networking capabilities, of NuttX. The article assumes that you are familiar with Linux, or any other Unix like operating system.

Nuttx Features

Some feature highlights of NuttX include:

  • Storage

    • MMC and SD card support

    • Flash support

    • USB Mass Storage support

  • Networking

    • TCP/IP stack

    • BSD socket API

    • DHCP server/client

    • FTP server/client

    • HTTP server/client

  • Filesystems

    • FAT filesystem support

    • Wear-leveling Flash filesystems

    • Network File System Client (NFS client)

    • ROM based filesystem support

  • Input

    • Touchscreen

    • USB Keyboard

    • Buttons (GPIO)

    • Keypads

  • Graphics

    • SPI based LCDs and OLEDs

    • Windowing system

    • Bitmap font rendering

    • GUI widget library

LM3S6965 Evaluation Kit and Qemu

We will need a target microcontroller board to try out NuttX. For this purpose we will emulate LM3S6965 Evaluation Kit using Qemu. Qemu is a system emulator that can emulate a wide range of processors and peripherals. For more information on Qemu, see

LM3S6965 is an ARM Cortex-M3 based microcontroller from TI’s Stellaris series. LM3S6965 has about 64KB on-chip RAM, and 256KB on-chip Flash. NuttX has been ported to this microcontroller, and specifically to the LM3S6965 Evaluation Kit. This makes it a great choice for trying out NuttX. The peripherals on the Evaluation Kit, support in Qemu and NuttX driver support, is tabulated below.

Feature Qemu Emulation NuttX Driver

Serial Port



SD Card

Read Only





OLED Display

Yes (Mostly)


Figure 1. LM3S6965 Evaluation Kit (Courtesy: Digikey)

Qemu version 0.14.0 or above is required to properly emulate the LM3S6965 Evaluation Kit. Make sure you download and install Qemu on your system. Qemu is part of most Linux distributions, so it is just a matter of invoking apt-get or yum with the appropriate package name. The instructions given in this tutorial correspond to Qemu version 0.22.0.

Debian users, please note that the version of Qemu distributed with Squeeze does not meet the requirement mentioned above. So you might want to compile a more recent version of Qemu yourself.


NuttShell (nsh) is a NuttX application, that allows the user to exercise capabilities of Nuttx, interactively. NuttShell is similar to Unix shells and provides many common Unix commands. When NuttShell runs on the target board, is accepts commands through the serial console. The shell can also be accessed by connecting through telnet.

The NuttShell application built for the LM3S6965 Evaluation Kit is available for download from the link below. The NuttShell executable contains both the NuttX kernel and the NuttShell application. An SD Card image, containing some files is also provided for testing purposes.

NuttX on the Emulated Target Board

The target board can be emulated, and NuttX can be executed on the board using the following command.

$ qemu-system-arm -M lm3s6965evb \
                  -kernel nuttx-nsh.elf \
                  -net user,hostfwd=tcp: \
                  -net nic,model=stellaris \
                  -sd sd.img

The -M lm3s6965evb option specifies the machine to be emulated, as LM3S6965 Evaluation Kit. The -kernel nuttx-nsh.elf option specifies the NuttShell application, is to be executed.

The target board is statically assigned an IP of, while compiling NuttShell. We will be using Qemu’s user mode networking capabilities to allow the target board to access the external network. For more details on user-mode networking, see

The -net user,hostfwd=tcp: option specifies user mode networking, with host port 2300 forwarded to guest port 23. This is done to allow connecting to the telnet server listening on port 23, in the guest. . The -net nic,model=stellaris option specifies that the Stellaris Ethernet controller, is the network interface card.

The -sd sd.img option specifies the image for the SD Card.

When Qemu starts up, the Qemu window by default shows the LCD display of LM3S6965 Evaluation Kit. Switch to the serial console using Alt-Ctrl-3 key combination. The NSH prompt should shown below should be visible on the serial console.

NuttShell (NSH) NuttX-6.24

Looking Around

The traditional ls command is available for listing files. Listing files shows a single /dev folder in the root filesystem. The /dev folder in turn contains a bunch of device files.

nsh> ls
nsh> ls dev

The ps command is available for listing the tasks running in the system.

nsh> ps
    0   0 FIFO KTHREAD   READY    Idle Task()
    1 100 FIFO TASK      RUNNING  <noname>()
    2 100 FIFO TASK      WAITSEM  <noname>()

The ps command shows an Idle Task and two other task. One of them probably corresponds to NSH and other the telnet server.

The help command, provides a list of commands available.

nsh> help
help usage:  help [-v] [<cmd>]

  [           exec        ifup        mkrd        pwd         unset
  ?           exit        kill        mh          rm          usleep
  cat         free        losetup     mount       rmdir       wget
  cd          get         ls          mv          set         xd
  cp          help        mb          mw          sh
  dd          hexdump     mkdir       ping        sleep
  df          ifconfig    mkfatfs     ps          test
  echo        ifdown      mkfifo      put         umount

Mounting a Ramdisk

The root filesystem is a virtual filesystem, just like /proc in Unix. And hence the filesystem is read-only. A ramdisk can be mounted to get access to a read/write filesystem. A ramdisk can be created using mkrd command.

The following command sequence creates a ramdisk, mounts it and creates file on it.

nsh> mkrd 40
nsh> mkfatfs /dev/ram0
nsh> mount -t vfat /dev/ram0 /tmp
nsh> echo "Hello World" > /tmp/hello.txt
nsh> ls /tmp
nsh> cat /tmp/hello.txt
Hello World

mkrd command is used to create a ramdisk. The argument specifies the size of the ramdisk in sectors. Once a ramdisk is created a device file /dev/ram0 becomes available. A filesystem can then be created and mounted. Note that the mount point /tmp, in this case, is automatically created by NuttX.

Accessing the SD Card

The SD Card can be accessed by mounting the block device /dev/mmcsd0. The following command sequence mounts the SD Card and prints the contents of a test file in the SD card. Note that, the SD Card image sd.img provided to Qemu is used for the contents of the SD Card.

nsh> mount -t vfat /dev/mmcsd0 /sd
nsh> ls /sd
nsh> cat /sd/test.txt
Hello World


As with any other Unix system, the active network interfaces can be listed using the ifconfig command.

nsh> ifconfig
eth0    HWaddr 00:e0:de:ad:be:ef at UP
        IPaddr: DRaddr: Mask:

uIP         IP   TCP  UDP  ICMP
Received    0000 0000 0000 0000
Dropped     0000 0000 0000 0000
  IP        VHL: 0000 HBL: 0000
            LBL: 0000 Frg: 0000
  Checksum  0000 0000 0000 ----
  TCP       ACK: 0000 SYN: 0000
            RST: 0000 0000
  Type      0000 ---- ---- 0000
Sent        ---- 0000 0000 0000
  Rexmit    ---- 0000 ---- ----

Connectivity to the gateway can be tested using the ping command. Note that, since we are using user-mode networking, ping systems on the external network will not work.

nsh> ping
PING 56 bytes of data
56 bytes from icmp_seq=2 time=0 ms
56 bytes from icmp_seq=3 time=0 ms
56 bytes from icmp_seq=4 time=0 ms
56 bytes from icmp_seq=5 time=0 ms
56 bytes from icmp_seq=6 time=0 ms
56 bytes from icmp_seq=7 time=0 ms
56 bytes from icmp_seq=8 time=0 ms
56 bytes from icmp_seq=9 time=0 ms
56 bytes from icmp_seq=10 time=0 ms
10 packets transmitted, 9 received, 10% packet loss, time 11130 ms

The NSH can be accessed through telnet as well. Telnet to the host port 2300, since guest port 23 has been forwarded to host port 2300. You should get the NSH prompt.

$ telnet localhost 2300
Connected to localhost.
Escape character is '^]'.

NuttShell (NSH) NuttX-6.24

NSH has TFTP get and put commands, and HTTP wget command. But we weren’t able to get this to work yet.

Concluding Notes

It’s amazing to see how much can be packed into a code size of just 94K! Hope this article has kindled your interest in NuttX. We will see how to build NuttX + NSH application, in a follow-up article.