NuttX RTOS

Last Updated: August 2, 2008

	Overview. What is NuttX?
	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.
	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 and serial driver architecture.
	Mount-able volumes. Bind mountpoint, filesystem, and block device driver.
	VFAT 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.

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

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

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

Downloads

The 23rd release of NuttX (nuttx-0.3.11) 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.

nuttx-0.3.11 is another important bugfix release. This release fixes several bugs:

Two POSIX timer bugs: a memory leak as well a fatal sequencing error.
Several FAT filesystem errors.
A deadlock that can occur in opendir()

A few new features were also added:

Support for recursive mutexes
Added a RAM disk block driver
The host simulator no longer uses direct Linux system calls and now also works on Cygwin.
The OS test was strengthen and now runs as an endurance test

As usual, any feedback about bugs or suggestions for improvement would be greatly appreciated.

Supported Platforms

	Linux User Mode
	A user-mode port of NuttX to the x86 Linux platform is available. The purpose of this port is primarily to support OS feature development. STATUS: Does not support interrupts but is otherwise fully functional.
	ARM7TDMI.
	TI TMS320C5471 (also called C5471 or TMS320DA180 or DA180). NuttX operates on the ARM7 of this dual core processor. This port uses the Spectrum Digital evaluation board with a GNU arm-elf toolchain* under Linux or Cygwin. STATUS: This port is complete, verified, and included in the initial NuttX release.
	NXP LPC214x. Support is provided for the NXP LPC214x family of processors. In particular, support is provided for the mcu123.com lpc214x evaluation board (LPC2148). This port also used the GNU arm-eld toolchain* under Linux or Cygwin. STATUS: Initial coding of this port code complete but has not yet been verified.
	ARM926EJS.
	TI TMS320DM320 (also called DM320). NuttX operates on the ARM9 of this dual core processor. This port uses the Neuros OSD with a GNU arm-elf toolchain* under Linux or Cygwin. STATUS: This port is complete and verified.
	8052 Microcontroller
	PJRC 87C52 Development Board. This port uses the PJRC 87C52 development system and the SDCC toolchain under Linux or Cygwin. STATUS: This port is complete but not stable with timer interrupts enabled. There seems to be some issue when the stack pointer enters into the indirect IRAM address space during interrupt handling. This architecture has not been built in some time will likely have some compilation problems because of SDCC compiler differences.
	Zilog Z16F
	Zilog z16f Microncontroller. This port use the Zilog z16f2800100zcog development kit and the Zilog ZDS-II Windows command line tools. The development environment is Cygwin under WinXP. STATUS: The initial release of support for the z16f was made available in NuttX version 0.3.7.
	Zilog eZ80Acclaim!
	Zilog eZ80Acclaim! Microncontroller. This port uses the ZiLOG ez80f0910200kitg development kit, eZ80F091 part and the Zilog ZDS-II Windows command line tools. The development environment is Cygwin under WinXP. STATUS: This is a work in progress. Verified ez80 support will be announced in a future NuttX release.
	Zilog Z8Encore!
	Zilog Z8Encore! Microncontroller. This port uses the either: Zilog z8encore000zco development kit, Z8F6403 part, or Zilog z8f64200100kit development kit, Z8F6423 part and the Zilog ZDS-II Windows command line tools. The development environment is Cygwin under WinXP. STATUS: This release has been verified only on the ZiLOG ZDS-II Z8Encore! chip simulation as of nuttx-0.3.9.
	Zilog Z80
	Z80 Instruction Set Simulator. This port uses the SDCC toolchain under Linux or Cygwin (verified using version 2.6.0). This port has been verified using only a Z80 instruction simulator. That simulator can be found in the NuttX CVS here. STATUS: This port is complete and stable to the extent that it can be tested using an instruction set simulator.
	Other ports
	There are partial ports for the TI TMS320DM270 and for MIPS.

* A highly modified buildroot is available that may be used to build a NuttX-compatible arm-elf toolchain under Linux or Cygwin.

Development Environments

	Linux + GNU make + GCC/binutils
	The is the most natural development environment for NuttX. Any version of the GCC/binutils toolchain may be used. There is a highly modified buildroot available for download from the NuttX SourceForge page. This download may be used to build a NuttX-compatible arm-elf toolchain under Linux or Cygwin. Additional support for m68k, m68hc11, and m68hc12 is available in the NuttX CVS.
	Linux + GNU make + SDCC
	Also very usable is the Linux environment using the SDCC compiler. The SDCC compiler provides support for the 8051/2, z80, hc08, and other microcontrollers. The SDCC-based logic is less well exercised and you will likely find some compilation issues if you use parts of NuttX with SDCC that have not been well-tested.
	Cygwin + GNU make + GCC/binutils
	This combination works well too. It works just as well as the native Linux environment except that compilation and build times are a little longer. The custom NuttX buildroot referenced above may be build in the Cygwin environment as well.
	Cygwin + GNU make + SDCC
	I have never tried this combination, but it would probably work just fine.
	Cygwin + GNU make + Windows Native Toolchain
	This is a tougher environment. In this case, the Windows native toolchain is unaware of the the Cygwin sandbox and, instead, operates in the native Windows environment. The primary difficulties with this are: Paths. Full paths for the native toolchain must follow Windows standards. For example, the path `/home/my\ name/nuttx/include` my have to be converted to something like `'C:\cygwin\home\my name\nuttx\include'` to be usable by the toolchain. Fortunately, this conversion is done simply using the `cygpath` utility. Symbolic Links NuttX depends on symbolic links to install platform-specific directories in the build system. On Linux, true symbolic links are used. On Cygwin, emulated symbolic links are used. Unfortunately, for native Windows applications that operate outside of the Cygwin sandbox, these symbolic links cannot be used. The NuttX make system works around this limitation by copying the platform specific directories in place. These copied directories make work a little more complex, but otherwise work well. At present, on the Zilog Z16F port uses a native Windows toolchain (the Zilog ZDS-II toolchain).
	Others Environments?
	The primary environmental dependency of NuttX are (1) GNU make, (2) bash scripting, and (3) Linux utilities (such as sed). If you have other platforms that support GNU make or make utilities that are compatible with GNU make, then it is very likely that NuttX would work in that environment as well (with some porting effort). If GNU make is not supported, then some significant modification of the Make system would be required.

Memory Footprint

C5471 (ARM7) The build for this ARM7 target that includes most of the OS features and a broad range of OS tests. The size of this executable as given by the Linux size command is (3/9/07):

   text    data     bss     dec     hex filename
  53272     428    3568   57268    dfb4 nuttx

DM320 (ARM9) This build for the ARM9 target includes a significant subset of OS features, a filesystem, Ethernet driver, full TCP/IP, UDP and (minimal) ICMP stacks (via uIP) and a small network test application: (11/8/07, configuration netconfig, examples/nettest)

   text    data     bss     dec     hex filename
  49472     296    3972   53740    d1ec nuttx

Another build for the ARM9 target includes a minimal OS feature set, Ethernet driver, full TCP/IP and (minimal) ICMP stacks, and a small webserver: (11/20/07, configuration uipconfig, examples/uip)

   text    data     bss     dec     hex filename
  52040      72    4148   56260    dbc4 nuttx

87C52 A reduced functionality OS test for the 8052 target requires only about 18-19Kb:

Stack starts at: 0x21 (sp set to 0x20) with 223 bytes available.

Other memory:
   Name             Start    End      Size     Max
   ---------------- -------- -------- -------- --------
   PAGED EXT. RAM                         0      256
   EXTERNAL RAM     0x0100   0x02fd     510     7936
   ROM/EPROM/FLASH  0x2100   0x6e55   19798    24384

Licensing

NuttX is available under the highly permissive BSD license. Other than some fine print that you agree to respect the copyright you should feel absolutely free to use NuttX in any environment and without any concern for jeopardizing any proprietary software that you may link with it.

Release History

The current NuttX Change Log is available in CVS here. ChangeLog snapshots associated with the current release are available below.

	Change Logs for All NuttX Releases
	ChangeLog for Current Releases
	Unreleased Changes

ChangeLog for Current Release


nuttx-0.3.11 2008-xx-xx Gregory Nutt <spudmonkey@racsa.co.cr>

	* Add support for recursive mutexes.
	* Eliminate a memory leak -- contained watchdog instance was not being
	  deleted with a POSIX timer was deleted reported by kwonsk.
	* Eliminate a deadlock condition in opendir() reported by kwonsk.
	* Fix several FAT filesystem problems reported by kwonsk (Changes not yet
	  verified).
	* Host simulator no longer uses Linux system calls directly; Now works with Cygwin.
	* Fix an error that occurs when a POSIX timer is deleted by the timer signal handler.
	* Add logic to allow the examples/ostest to be run repetitively as an endurance test.
	* Add a ramdisk block driver

pascal-0.1.2 2008-02-10 Gregory Nutt 

	* Add logic to build and link with the ZDS-II toolchain
	  use with the z16f.
	* Make sure that POFF header structures are aligned
	* Standardized POFF file format to big-endian
	* Break up large switch statements to lower complexity
	  and eliminate a compiler bug
	* Changes so that runtime compiles with SDCC.

buildroot-0.1.0 2007-03-09 <spudmonkey@racsa.co.cr>

	* Support for arm-elf toolchain

Unreleased Changes


nuttx-0.3.12 2008-xx-xx Gregory Nutt <spudmonkey@racsa.co.cr>

	* Improved solution to POSIX timer lifetime controls bug fixed in 0.3.11.
	* Add test for recursive mutexes
	* Correct bug in recursive mutex logic
	* Add mkfifo()
	* Add pipe() and test for both pipes and fifos
	* Attempts to open a FIFO will now block until there is at least one writer
	* Add test/Fixed errors in FIFO reader/writer interlocks
	* Removed limitation: task_create() was only dup'ing 3 file descriptors (now
	  dups all open file descriptors).
	* Added a test for redirection of stdio through pipes
	* Fixed error in dup and dup2: Must call open/close methods in fs/driver so that
	  driver can correctly maintain open reference counts.
	* Same issue on closing file descriptors in exit()
	* Fixed in error in stdio flush logic.  Needed ssize_t vs size_t for error
	  check.
	* Moved all FAT related files from fs to fs/fat

pascal-0.1.3 2008-xx-xx Gregory Nutt <spudmonkey@racsa.co.cr>

buildroot-0.1.1 2008-xx-xx <spudmonkey@racsa.co.cr>

	* Support for m68k-elf and m68hc11 toolchain

Bugs, Issues, Things-To-Do

The current list of NuttX Things-To-Do in CVS here. A snapshot of the To-Do list associated with the current release are available here.

Trademarks

ARM, ARM7 ARM7TDMI, ARM9, ARM926EJS are trademarks of Advanced RISC Machines, Limited.
Cygwin is a trademark of Red Hat, Incorporated.
Linux is a registered trademark of Linus Torvalds.
LPC2148 is a trademark of NXP Semiconductors.
TI is a tradename of Texas Instruments Incorporated.
UNIX is a registered trademark of The Open Group.
VxWorks is a registered trademark of Wind River Systems, Incorporated.
ZDS, ZNEO, Z16F, Z80, and Zilog are a registered trademark of Zilog, Inc.

NOTE: NuttX is not licensed to use the POSIX trademark. NuttX uses the POSIX standard as a development guideline only.