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NuttX Operating System
User's Manual
by
Gregory Nutt
Last Updated: December 13, 2009
1.0 Introduction
This manual provides general usage information for the NuttX RTOS from the perspective of the
firmware developer.
1.1 Document Overview
This user's manual is divided into three sections plus a index:
Section 1.0, Introduction: This section provides an overview of the NuttX user's manual.
Section 2.0, OS Interfaces: This section details the program interfaces provided by NuttX.
This section is divided into several paragraphs that describe different groups of OS interfaces:
Paragraph 2.1 Task Control Interfaces
Paragraph 2.2 Task Scheduling Interfaces
Paragraph 2.3 Task Switching Interfaces
Paragraph 2.4 Named Message Queue Interfaces
Paragraph 2.5 Counting Semaphore Interfaces
Paragraph 2.6 Watchdog Timer Interfaces
Paragraph 2.7 Clocks and Timers
Paragraph 2.8 Signal Interfaces
Paragraph 2.9 Pthread Interfaces
Paragraph 2.10 Environment Variables
Paragraph 2.11 File System Interfaces
Paragraph 2.12 Network Interfaces
Section 3.0, OS Data Structures: This section documents the data structures that are used at
the NuttX interface.
Paragraph 3.1 Scalar Types
Paragraph 3.2 Hidden Interface Structures
Paragraph 3.3 Access to the errno Variable
Paragraph 3.4 User Interface Structures
Index
1.2 Intended Audience and Scope

The intended audience for this document are firmware developers who are implementing

applications on NuttX. Specifically, this documented is limited to addressing only NuttX RTOS APIs

that are available to the application developer. As such, this document does not focus on any

technical details of the organization or implementation of NuttX. Those technical details are

provided in the NuttX Porting Guide.

Information about configuring and building NuttX is also needed by the application developer.

That information can also be found in the NuttX Porting Guide.

2.0 OS Interfaces

This section describes each C-callable interface to the NuttX Operating System. The description of

each interface is presented in the following format:

Function Prototype: The C prototype of the interface function is provided.

Description: The operation performed by the interface function is discussed.

Input Parameters: All input parameters are listed along with brief descriptions of each input

parameter.

Returned Values: All possible values returned by the interface function are listed. Values returned

as side-effects (through pointer input parameters or through global variables) will be addressed in

the description of the interface function.

Assumptions/Limitations: Any unusual assumptions made by the interface function or any non-

obvious limitations to the use of the interface function will be indicated here.

POSIX Compatibility: Any significant differences between the NuttX interface and its

corresponding POSIX interface will be noted here.

NOTE: In order to achieve an independent name space for the NuttX interface functions,

differences in function names and types are to be expected and will not be identified as differences

in these paragraphs.

2.1 Task Control Interfaces

Tasks. NuttX is a flat address OS. As such it does not support

processes

in the way that, say, Linux

does. NuttX only supports simple threads running within the same address space. However, the

programming model makes a distinction between

tasks

and

pthreads

tasks

are threads which have a degree of independence

pthreads

share some resources.

File Descriptors and Streams. This applies, in particular, in the area of opened file descriptors and

streams. When a task is started using the interfaces in this section, it will be created with at most

three open files.

If CONFIG_DEV_CONSOLE is defined, the first three file descriptors (corresponding to stdin, stdout,

stderr) will be duplicated for the new task. Since these file descriptors are duplicated, the child task

can free close them or manipulate them in any way without effecting the parent task. File-related

operations (open, close, etc.) within a task will have no effect on other tasks. Since the three file

descriptors are duplicated, it is also possible to perform some level of redirection.

pthreads, on the other hand, will always share file descriptors with the parent thread. In this case,

file operations will have effect only all pthreads the were started from the same parent thread.

Executing Programs within a File System. NuttX also provides internal interfaces for the

execution of separately built programs that reside in a file system. These internal interfaces are,

however, non-standard and are documented elsewhere.

Task Control Interfaces. The following task control interfaces are provided by NuttX:

2.1.1 task_create

2.1.2 task_init

2.1.3 task_activate

2.1.4 task_delete

2.1.5 exit

2.1.6 task_restart

2.1.7 getpid

2.1.1 task_create

Function Prototype:

#include <sched.h>

int task_create(char *name, int priority, int stack_size, main_t entry, const char *argv[]);

Description: This function creates and activates a new task with a specified priority and returns its

system-assigned ID.

The entry address entry is the address of the "main" function of the task. This function will be

called once the C environment has been set up. The specified function will be called with four

arguments. Should the specified routine return, a call to exit() will automatically be made.

Note that an arbitrary number of arguments may be passed to the spawned functions. The

maximum umber of arguments is an OS configuration parameter (CONFIG_MAX_TASK_ARGS).

The arguments are copied (via strdup) so that the life of the passed strings is not dependent on the

life of the caller to task_create().

The newly created task does not inherit scheduler characteristics from the parent task: The new

task is started at the default system priority and with the SCHED_FIFO scheduling policy. These

characteristics may be modified after the new task has been started.

The newly created task does inherit the first three file descriptors (corresponding to stdin, stdout,

and stderr) and redirection of standard I/O is supported.

Input Parameters:

name

. Name of the new task

priority

. Priority of the new task

stack_size

. size (in bytes) of the stack needed

entry

. Entry point of a new task

argv

. A pointer to an array of input parameters. Up to CONFIG_MAX_TASK_ARG parameters may be

provided. If fewer than CONFIG_MAX_TASK_ARG parameters are passed, the list should be terminated

with a NULL argv[] value. If no parameters are required, argv may be NULL.

Returned Values:

Returns the non-zero task ID of the new task or ERROR if memory is insufficient or the task

cannot be created (errno is not set).

Assumptions/Limitations:

POSIX Compatibility: This is a NON-POSIX interface. VxWorks provides the following similar

interface:

int taskSpawn(char *name, int priority, int options, int stackSize, FUNCPTR entryPt,

int arg1, int arg2, int arg3, int arg4, int arg5,

int arg6, int arg7, int arg8, int arg9, int arg10);

The NuttX task_create() differs from VxWorks' taskSpawn() in the following ways:

Interface name

Various differences in types of arguments

There is no options argument.

A variable number of parameters can be passed to a task (VxWorks supports ten).

2.1.2 task_init

Function Prototype:

#include <sched.h>

int task_init(_TCB *tcb, char *name, int priority, uint32_t *stack, uint32_t stack_size,

maint_t entry, const char *argv[]);

Description:

This function initializes a Task Control Block (TCB) in preparation for starting a new thread. It

performs a subset of the functionality of task_create() (see above).

Unlike task_create(), task_init() does not activate the task. This must be done by calling

task_activate().

Input Parameters:

tcb

. Address of the new task's TCB

name

. Name of the new task (not used)

priority

. Priority of the new task

stack

. Start of the pre-allocated stack

stack_size

. size (in bytes) of the pre-allocated stack

entry

. Entry point of a new task

argv

. A pointer to an array of input parameters. Up to CONFIG_MAX_TASK_ARG parameters may be

provided. If fewer than CONFIG_MAX_TASK_ARG parameters are passed, the list should be terminated

with a NULL argv[] value. If no parameters are required, argv may be NULL.

Returned Values:

OK, or ERROR if the task cannot be initialized.

This function can only failure is it is unable to assign a new, unique task ID to the TCB (errno is

not set).

Assumptions/Limitations:

task_init() is provided to support internal OS functionality. It is not recommended for normal

usage. task_create() is the preferred mechanism to initialize and start a new task.

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