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

1. Small Footprint

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

2. Rich Feature OS Set

The goal is to provide most standard POSIX OS interfaces to support a rich multi-threaded development environment.

NON-GOALS: (1) It is not a goal to provide OS subsystems such as network or USB (but these could obviously be added). (2) There is no MMU-based support for processes. At present, NuttX assumes a flat address space.
3. 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.

4. 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 functionaly 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.

5. Real-Time

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

6. Totally Open

Non-restrictive BSD license.

The initial release of NuttX (nuttx-0.1.0) is avalable for download from the SourceForge website.

• 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 developement.

STATUS: Does not support interrupts but is otherwise fully functional.

• TI TMS320C5471 (also called TMS320DM180).

NuttX operates on the ARM7 of this dual core processor. This port uses the Spectrum Digital evaluation board with a GNU arm-elf toolchain*.

STATUS: This port is complete, verified, and included in the initial NuttX release.

• 8051 Microcontroller

This port uses the PJRC 87C52 development system and the SDCC toolchain.

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.

• Other ports

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

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

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

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

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.

0.1.0 2007-03-09  Gregory Nutt 

	* Initial Release
	* Support for Linux user mode simulation and TI
	  TMS320C5471 (Arm7) provided

0.1.1 2007-03-14  Gregory Nutt 

	* Corrected an error in interrupt level context switching
	  for C5471
	* Added fgets() and gets() logic; verified c5471 console read.
	* Corrected error in reading from the C5471 serial port:
          Improper use of semaphore can cause deadlock.
	* Fixed an error in the memory cleanup:  The idle task
	  cannot take sempahores (because it must always be ready
	  to run).
	* Tasks can now accept a configurable maximum number of
	  input parameters (argc)
	* _task_init() was divided into separate functions that
	  require fewer parameters.  This was necessary to keep
	  the stack usage down for the 8051/2 (which has only
	  256 bytes of stack).
	* Attempts to use C5471 console from interrupt handlers
	  can casue errors. Added a special path for this case.
	* Refuse calls to sem_wait and sem_trywait from interrupt
	  handlers.  This was happening because interrupt handlers
	  were calling printf-like functions.
	* Added strtok() and strtok_r()
	* Added a simple shell called nsh (see examples/nsh).
	* Platform support for 8052 is complete but not stable
	  when the timer interrupt is enabled.  Seems to be an
	  issue when SP enters indirect address space.
	* Documentation updates