NuttX RTOS

Last Updated: February 28, 2009

Table of Contents
Overview.
What is NuttX? Look at all those files and features... How can it be a tiny OS?
Downloads.
Where can I get NuttX? What is the current development status?
Supported Platforms.
What target platforms has NuttX been ported to?
Development Environments.
What kinds of host cross-development platforms can be used with NuttX?
Memory Footprint.
Just how big is it? Do I have enough memory to use NuttX?
Licensing.
Are there any licensing restrictions for the use of NuttX? (Almost none) Will there be problems if I link my proprietary code with NuttX? (No)
Release History
What has changed in the last release of NuttX? What unreleased changes are pending in CVS?
Bugs, Issues, Things-To-Do.
Software is never finished nor ever tested well enough. (Do you want to help develop NuttX? If so, send me an email).
Other Documentation.
What other NuttX documentation is available?
Trademarks.
Some of the words used in this document belong to other people.

Overview

Goals. Nuttx is a real timed embedded operating system (RTOS). Its goals are:

Small Footprint

Usable in all but the tightest micro-controller environments, The focus is on the tiny-to-small, deeply embedded environment.

Rich Feature OS Set

The goal is to provide implementations of most standard POSIX OS interfaces to support a rich, multi-threaded development environment for deeply embedded processors.

NON-GOALS: (1) It is not a goal to provide the rich level of OS features like those provided with Linux. Small footprint is more important than features. Standard compliance is more important than small footprint. (2) There is no MMU-based support for processes. At present, NuttX assumes a flat address space.

Highly Scalable

Fully scalable from tiny (8-bit) to moderate embedded (32-bit). Scalability with rich feature set is accomplished with: Many tiny source files, link from static libraries, highly configurable, use of weak symbols when available.

Standards Compliance

NuttX strives to achieve a high degree of standards compliance. The primary governing standards are POSIX and ANSI standards. Additional standard APIs from Unix and other common RTOS's are adopted for functionality not available under these standards or for functionality that is not appropriate for the deeply-embedded RTOS (such as fork()).

Because of this standards conformance, software developed under other standard OSs (such as Linux) should port easily to NuttX.

Real-Time

Fully pre-emptible, fixed priority and round-robin scheduling.

Totally Open

Non-restrictive BSD license.

Feature Set. Key features of NuttX include:

Standards Compliant Core Task Management

  • Modular, micro-kernel


    		•

  • Fully pre-emptible.


    		•

  • Naturally scalable.


    		•

  • Highly configurable.


    		•

  • Easily extensible to new processor architectures, SoC architecture, or board architectures. A Porting Guide is in development.


    		•

  • FIFO and round-robin scheduling.


    		•

  • Realtime, deterministic.


    		•

  • POSIX/ANSI-like task controls, named message queues, counting semaphores, clocks/timers, signals, pthreads, environment variables, filesystem.


    		•

  • VxWorks-like task management and watchdog timers.


    		•

  • BSD socket interface.


    		•

  • Extensions to manage pre-emption.


    		•

  • Well documented in the NuttX User Guide.

    • File system

  • Tiny in-memory, root pseudo-file-system.


    		•

  • Supports character and block drivers.


    		•

  • Network, USB (device), serial, CAN, driver architecture.


    		•

  • RAMDISK, pipes, FIFO, /dev/null, /dev/zero drivers.


    		•

  • Mount-able volumes. Bind mountpoint, filesystem, and block device driver.


    		•

  • FAT12/16/32 filesystem support.


    		•

  • Generic driver for SPI-based MMC/SD cards.


    		•

  • ROMFS filesystem support.

    • C Library

  • Fully integrated into the OS.

    • Networking

  • TCP/IP, UDP, ICMP stacks.


    		•

  • Small footprint (based on uIP).


    		•

  • BSD compatible socket layer.


    		•

  • Networking utilities (DHCP, SMTP, TELNET, TFTP, HTTP)

    • USB Device Support

  • Gadget-like architecture for USB device controller drivers and device-dependent USB class drivers.


    		•

  • USB device controller drivers available for the NXP LPC214x and TI DM320.


    		•

  • Device-dependent USB class drivers available for USB serial and for USB mass storage.


    		•

  • Built-in USB trace functionality for USB debug.

    • Graphics Support

  • Framebuffer drivers.


    		•

  • NX: A graphics library, tiny windowing system and tiny font support. Documented in the NX Graphics Subsystem manual.

    • NuttX Add-Ons. The following packages are available to extend the basic NuttX feature set:

    NuttShell (NSH)

  • A small, scalable, bash-like shell for NuttX with rich feature set and small footprint. See the NuttShell User Guide.

    • Pascal Compiler with NuttX runtime P-Code interpreter add-on

  • The Pascal add-on is available for download from the SourceForge website.

    		•

    Look at all those files and features... How can it be a tiny OS?. The NuttX feature list (above) is fairly long and if you look at the NuttX source tree, you will see that there are hundreds of source files comprising NuttX. How can NuttX be a tiny OS with all of that?

    Lots of Features -- More can be smaller!

    The philosophy behind that NuttX is that lots of features are great... BUT also that if you don't use those features, then you should not have to pay a penalty for the unused features. And, with NuttX, you don't! If you don't use a feature, it will not be included in the final executable binary. You only have to pay the penalty of increased footprint for the features that you actually use.

    Using a variety of technologies, NuttX can scale from the very tiny to the moderate-size system. I have executed NuttX with some simple applications in as little as 32Kb total memory (code and data). On the other hand, typical, richly featured NuttX builds require more like 64Kb (and if all of the features are used, this can push 100Kb).

    Many, many files -- More really is smaller!

    One may be intimidated by the size NuttX source tree. There are hundreds of source files! How can that be a tiny OS? Actually, the large number of files is one of the tricks to keep NuttX small and as scalable as possible. Most files contain only a single function. Sometimes just one tiny function with only a few lines of code. Why?

    • Static Libraries. Because in the NuttX build processed, objects are compiled and saved into static libraries (archives). Then, when the file executable is linked, only the object files that are needed are extracted from the archive and added to the final executable. By having many, many tiny source files, you can assure that no code that you do not execute is ever included in the link. And by having many, tiny source files you have better granularity -- if you don't use that tiny function of even just a few lines of code, it will not be included in the binary.
    Other Tricks

    As mentioned above, the use of many, tiny source files and linking from static libraries keeps the size of NuttX down. Other tricks used in NuttX include:

    • Configuration Files. Before you build NuttX, you must provide a configuration file that specifies what features you plan to use and which features you do not. This configuration file contains a long list of settings that control what is built into NuttX and what is not. There are hundreds of such settings (see the NuttX Porting Guide for a partial list that excludes platform specific settings). These many, many configuration options allow NuttX to be highly tuned to meet size requirements. The downside to all of these configuration options is that it greatly complicates the maintenance of NuttX -- but that is my problem, not yours.
    • Weak Symbols The GNU toolchain supports weak symbols and these also help to keep the size of NuttX down. Weak symbols prevent object files from being drawn into the link even if they are accessed from source code. Careful use of weak symbols is another trick for keep unused code out of the final binary.

    Downloads

    nuttx-0.4.2. The 34th release of NuttX (nuttx-0.4.2) is available for download from the SourceForge website. The change log associated with the release is available here. Unreleased changes after this release are available in CVS. These unreleased changes are listed here.

    This release adds no new OS features but does include support for two new architectures:

    Unreleased Changes

    Bugs, Issues, Things-To-Do

    Other Documentation