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.
Fig. 18 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).
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.
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.
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:
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:
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.
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.
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.
API |
Supported |
|---|---|
abort() |
yes |
alarm() |
|
kill() |
|
pause() |
|
raise() |
|
sigaction() |
|
igaddset() |
|
sigdelset() |
|
sigemptyset() |
|
sigfillset() |
|
igismember() |
|
signal() |
|
sigpending() |
|
sigprocmask() |
|
igsuspend() |
|
sigwait() |
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() |