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

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

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.

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.

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

Non-restrictive BSD license.

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.

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.

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.

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 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: This is a work in progress.

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.

There are partial ports for the TI TMS320DM270 and for MIPS.

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.

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.

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.

I have never tried this combination, but it would probably work just fine.

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).

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.