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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

Fig. 20 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).

Table 8 Units of Functionality

Requirements

Supported

Remarks

POSIX_C_LANG_JUMP

POSIX_C_LANG_SUPPORT

yes

POSIX_DEVICE_IO

POSIX_FILE_LOCKING

POSIX_SIGNALS

POSIX_SINGLE_PROCESS

POSIX_THREADS_BASE

yes

XSI_THREAD_MUTEX_EXT

yes

XSI_THREADS_EXT

yes

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.

Table 9 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

yes

_POSIX_SHARED_MEMORY_OBJECTS

_POSIX_SYNCHRONIZED_IO

_POSIX_THREAD_ATTR_STACKADDR

_POSIX_THREAD_ATTR_STACKSIZE

_POSIX_THREAD_CPUTIME

_POSIX_THREAD_PRIO_INHERIT

yes

_POSIX_THREAD_PRIO_PROTECT

_POSIX_THREAD_PRIORITY_SCHEDULING

yes

_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.

Table 10 POSIX_THREADS_BASE

API

Supported

pthread_atfork()

pthread_attr_destroy()

yes

pthread_attr_getdetachstate()

yes

pthread_attr_getschedparam()

yes

pthread_attr_init()

yes

pthread_attr_setdetachstate()

yes

pthread_attr_setschedparam()

yes

pthread_cancel()

yes

pthread_cleanup_pop()

pthread_cleanup_push()

pthread_cond_broadcast()

yes

pthread_cond_destroy()

pthread_cond_init()

yes

pthread_cond_signal()

yes

pthread_cond_timedwait()

yes

pthread_cond_wait()

yes

pthread_condattr_destroy()

pthread_condattr_init()

pthread_create()

yes

pthread_detach()

yes

pthread_equal()

pthread_exit()

yes

pthread_getspecific()

yes

pthread_join()

yes

pthread_key_create()

yes

pthread_key_delete()

yes

pthread_kill()

pthread_mutex_destroy()

yes

pthread_mutex_init()

yes

pthread_mutex_lock()

yes

pthread_mutex_trylock()

yes

pthread_mutex_unlock()

yes

pthread_mutexattr_destroy()

pthread_mutexattr_init()

pthread_once()

yes

pthread_self()

yes

pthread_setcalcelstate()

pthread_setcanceltype()

pthread_setspecific()

yes

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:

Table 11 XSI_THREAD_EXT

API

Supported

pthread_attr_getguardsize()

pthread_attr_getstack()

yes

pthread_attr_setguardsize()

pthread_attr_setstack()

yes

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:

Table 12 XSI_THREAD_MUTEX_EXT

API

Supported

pthread_mutexattr_gettype()

yes

pthread_mutexattr_settype()

yes

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.

Table 13 POSIX_C_LANG_SUPPORT

API

Supported

abs()

yes

asctime()

asctime_r()

atof()

atoi()

yes

atol()

atoll()

bsearch()

yes

calloc()

yes

ctime()

ctime_r()

difftime()

div()

feclearexcept()

fegetenv()

fegetexceptflag()

fegetround()

feholdexcept()

feraiseexcept()

fesetenv()

fesetexceptflag()

fesetround()

fetestexcept()

feupdateenv()

free()

yes

gmtime()

yes

gmtime_r()

yes

imaxabs()

imaxdiv()

isalnum()

yes

isalpha()

yes

isblank()

iscntrl()

isdigit()

yes

isgraph()

yes

islower()

isprint()

yes

ispunct()

isspace()

yes

isupper()

yes

isxdigit()

yes

labs()

yes

ldiv()

llabs()

yes

lldiv()

localeconv()

localtime()

yes

localtime_r()

malloc()

yes

memchr()

yes

memcmp()

yes

memcpy()

yes

memmove()

yes

memset()

yes

mktime()

yes

qsort()

rand()

yes

rand_r()

realloc()

yes

setlocale()

snprintf()

yes

sprintf()

yes

srand()

yes

sscanf()

strcat()

yes

strchr()

yes

strcmp()

yes

strcoll()

strcpy()

yes

strcspn()

strerror()

yes

strerror_r()

yes

strftime()

strlen()

yes

strncat()

yes

strncmp()

yes

strncpy()

yes

strpbrk()

strrchr()

yes

strspn()

strstr()

yes

strtod()

strtof()

strtoimax()

strtok()

strtok_r()

yes

strtol()

yes

strtold()

strtoll()

yes

strtoul()

yes

strtoull()

yes

strtoumax()

strxfrm()

time()

yes

tolower()

yes

toupper()

yes

tzname()

tzset()

va_arg()

va_copy()

va_end()

va_start()

vsnprintf()

yes

vsprintf()

yes

vsscanf()

POSIX_SINGLE_PROCESS

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

Table 14 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.

Table 15 POSIX_SIGNALS

API

Supported

abort()

yes

alarm()

kill()

pause()

raise()

sigaction()

igaddset()

sigdelset()

sigemptyset()

sigfillset()

igismember()

signal()

sigpending()

sigprocmask()

igsuspend()

sigwait()

POSIX_DEVICE_IO

Table 16 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()

yes

fputc()

yes

fputs()

yes

fread()

freopen()

fscanf()

fwrite()

yes

getc()

getchar()

gets()

open()

yes

perror()

yes

printf()

yes

putc()

yes

putchar()

puts()

yes

read()

yes

scanf()

setbuf()

etvbuf()

stderr

stdin

stdout

ungetc()

vfprintf()

yes

vfscanf()

vprintf()

yes

vscanf()

write()