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POSIX Support

The Portable Operating System Interface (POSIX) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. Zephyr implements a subset of the embedded profiles PSE51 and PSE52, and BSD Sockets API.

With the POSIX support available in Zephyr, an existing POSIX compliant application can be ported to run on the Zephyr kernel, and therefore leverage Zephyr features and functionality. Additionally, a library designed for use with POSIX threading compatible operating systems can be ported to Zephyr kernel based applications with minimal or no changes.

POSIX Support in Zephyr

POSIX support in Zephyr

The POSIX API subset is an increasingly popular OSAL (operating system abstraction layer) for IoT and embedded applications, as can be seen in Zephyr, AWS:FreeRTOS, TI-RTOS, and NuttX.

Benefits of POSIX support in Zephyr include:

  • Offering a familiar API to non-embedded programmers, especially from Linux

  • Enabling reuse (portability) of existing libraries based on POSIX APIs

  • Providing an efficient API subset appropriate for small (MCU) embedded systems

System Overview

Units of Functionality

The system profile is defined in terms of component profiles that specify Units of Functionality that can be combined to realize the application platform. A Unit of Functionality is a defined set of services which can be implemented. If implemented, the standard prescribes that all services in the Unit must be implemented.

A Minimal Realtime System Profile implementation must support the following Units of Functionality as defined in IEEE Std. 1003.1 (also referred to as POSIX.1-2017).

Units of Functionality

Requirements

Supported

Remarks

POSIX_C_LANG_JUMP

POSIX_C_LANG_SUPPORT

POSIX_DEVICE_IO

POSIX_FILE_LOCKING

POSIX_SIGNALS

POSIX_SINGLE_PROCESS

POSIX_THREADS_BASE

XSI_THREAD_MUTEX_EXT

XSI_THREADS_EXT

Option Requirements

An implementation supporting the Minimal Realtime System Profile must support the POSIX.1 Option Requirements which are defined in the standard. Options Requirements are used for further sub-profiling within the units of functionality: they further define the functional behavior of the system service (normally adding extra functionality). Depending on the profile to which the POSIX implementation complies,parameters and/or the precise functionality of certain services may differ.

The following list shows the option requirements that are implemented in Zephyr.

Option Requirements

Requirements

Supported

_POSIX_CLOCK_SELECTION

_POSIX_FSYNC

_POSIX_MEMLOCK

_POSIX_MEMLOCK_RANGE

_POSIX_MONOTONIC_CLOCK

_POSIX_NO_TRUNC

_POSIX_REALTIME_SIGNALS

_POSIX_SEMAPHORES

_POSIX_SHARED_MEMORY_OBJECTS

_POSIX_SYNCHRONIZED_IO

_POSIX_THREAD_ATTR_STACKADDR

_POSIX_THREAD_ATTR_STACKSIZE

_POSIX_THREAD_CPUTIME

_POSIX_THREAD_PRIO_INHERIT

_POSIX_THREAD_PRIO_PROTECT

_POSIX_THREAD_PRIORITY_SCHEDULING

_POSIX_THREAD_SPORADIC_SERVER

_POSIX_TIMEOUTS

_POSIX_TIMERS

_POSIX2_C_DEV

_POSIX2_SW_DEV

Units of Functionality

This section describes the Units of Functionality (fixed sets of interfaces) which are implemented (partially or completely) in Zephyr. Please refer to the standard for a full description of each listed interface.

POSIX_THREADS_BASE

The basic assumption in this profile is that the system consists of a single (implicit) process with multiple threads. Therefore, the standard requires all basic thread services, except those related to multiple processes.

POSIX_THREADS_BASE

API

Supported

pthread_atfork()

pthread_attr_destroy()

pthread_attr_getdetachstate()

pthread_attr_getschedparam()

pthread_attr_init()

pthread_attr_setdetachstate()

pthread_attr_setschedparam()

pthread_cancel()

pthread_cleanup_pop()

pthread_cleanup_push()

pthread_cond_broadcast()

pthread_cond_destroy()

pthread_cond_init()

pthread_cond_signal()

pthread_cond_timedwait()

pthread_cond_wait()

pthread_condattr_destroy()

pthread_condattr_init()

pthread_create()

pthread_detach()

pthread_equal()

pthread_exit()

pthread_getspecific()

pthread_join()

pthread_key_create()

pthread_key_delete()

pthread_kill()

pthread_mutex_destroy()

pthread_mutex_init()

pthread_mutex_lock()

pthread_mutex_trylock()

pthread_mutex_unlock()

pthread_mutexattr_destroy()

pthread_mutexattr_init()

pthread_once()

pthread_self()

pthread_setcalcelstate()

pthread_setcanceltype()

pthread_setspecific()

pthread_sigmask()

pthread_testcancel()

XSI_THREAD_EXT

The XSI_THREADS_EXT Unit of Functionality is required because it provides functions to control a thread’s stack. This is considered useful for any real-time application.

This table lists service support status in Zephyr:

XSI_THREAD_EXT

API

Supported

pthread_attr_getguardsize()

pthread_attr_getstack()

pthread_attr_setguardsize()

pthread_attr_setstack()

pthread_getconcurrency()

pthread_setconcurrency()

XSI_THREAD_MUTEX_EXT

The XSI_THREAD_MUTEX_EXT Unit of Functionality is required because it has options for controlling the behavior of mutexes under erroneous application use.

This table lists service support status in Zephyr:

XSI_THREAD_MUTEX_EXT

API

Supported

pthread_mutexattr_gettype()

pthread_mutexattr_settype()

POSIX_C_LANG_SUPPORT

The POSIX_C_LANG_SUPPORT Unit of Functionality contains the general ISO C Library.

This is implemented as part of the minimal C library available in Zephyr.

POSIX_C_LANG_SUPPORT

API

Supported

abs()

asctime()

asctime_r()

atof()

atoi()

atol()

atoll()

bsearch()

calloc()

ctime()

ctime_r()

difftime()

div()

feclearexcept()

fegetenv()

fegetexceptflag()

fegetround()

feholdexcept()

feraiseexcept()

fesetenv()

fesetexceptflag()

fesetround()

fetestexcept()

feupdateenv()

free()

gmtime()

gmtime_r()

imaxabs()

imaxdiv()

isalnum()

isalpha()

isblank()

iscntrl()

isdigit()

isgraph()

islower()

isprint()

ispunct()

isspace()

isupper()

isxdigit()

labs()

ldiv()

llabs()

lldiv()

localeconv()

localtime()

localtime_r()

malloc()

memchr()

memcmp()

memcpy()

memmove()

memset()

mktime()

qsort()

rand()

rand_r()

realloc()

setlocale()

snprintf()

sprintf()

srand()

sscanf()

strcat()

strchr()

strcmp()

strcoll()

strcpy()

strcspn()

strerror()

strerror_r()

strftime()

strlen()

strncat()

strncmp()

strncpy()

strpbrk()

strrchr()

strspn()

strstr()

strtod()

strtof()

strtoimax()

strtok()

strtok_r()

strtol()

strtold()

strtoll()

strtoul()

strtoull()

strtoumax()

strxfrm()

time()

tolower()

toupper()

tzname()

tzset()

va_arg()

va_copy()

va_end()

va_start()

vsnprintf()

vsprintf()

vsscanf()

POSIX_SINGLE_PROCESS

The POSIX_SINGLE_PROCESS Unit of Functionality contains services for single process applications.

POSIX_SINGLE_PROCESS

API

Supported

confstr()

environ

errno

getenv()

setenv()

sysconf()

uname()

unsetenv()

POSIX_SIGNALS

Signal services are a basic mechanism within POSIX-based systems and are required for error and event handling.

POSIX_SIGNALS

API

Supported

abort()

alarm()

kill()

pause()

raise()

sigaction()

igaddset()

sigdelset()

sigemptyset()

sigfillset()

igismember()

signal()

sigpending()

sigprocmask()

igsuspend()

sigwait()

POSIX_DEVICE_IO

POSIX_DEVICE_IO

API

Supported

flockfile()

ftrylockfile()

funlockfile()

getc_unlocked()

getchar_unlocked()

putc_unlocked()

putchar_unlocked()

clearerr()

close()

fclose()

fdopen()

feof()

ferror()

fflush()

fgetc()

fgets()

fileno()

fopen()

fprintf()

fputc()

fputs()

fread()

freopen()

fscanf()

fwrite()

getc()

getchar()

gets()

open()

perror()

printf()

putc()

putchar()

puts()

read()

scanf()

setbuf()

etvbuf()

stderr

stdin

stdout

ungetc()

vfprintf()

vfscanf()

vprintf()

vscanf()

write()