.TH intro "3rtapi" "2006-10-02" "LinuxCNC Documentation" "RTAPI"
.SH NAME

rtapi \- Introduction to the RTAPI API

.SH DESCRIPTION
RTAPI is a library providing a uniform API for several real time operating
systems.  As of LinuxCNC 2.7, POSIX threads and RTAI are supported.

.SH HEADER FILES
.SS rtapi.h
The file \fBrtapi.h\fR defines the RTAPI for both realtime and non-realtime
code.  This is a change from Rev 2, where the non-realtime (user space) API
was defined in ulapi.h and used different function names.  The symbols RTAPI
and ULAPI are used to determine which mode is being compiled, RTAPI for
realtime and ULAPI for non-realtime.

.SS rtapi_math.h
The file \fRrtapi_math.h\fR defines floating-point functions and constants.
It should be used instead of \fR<math.h>\fR in rtapi real-time components.

.SS rtapi_string.h
The file \fRrtapi_string.h\fR defines string-related functions.
It should be used instead of \fR<string.h>\fR in rtapi real-time components.

.SS rtapi_byteorder.h
This file defines the preprocessor macros RTAPI_BIG_ENDIAN,
RTAPI_LITTLE_ENDIAN, and RTAPI_FLOAT_BIG_ENDIAN as true or false depending on
the characteristics of the target system.  It should be used instead of
\fB<endian.h>\fR (userspace) or \fB<linux/byteorder.h>\fR (kernel space).

.SS rtapi_limits.h
This file defines the minimum and maximum value of some fundamental integral
types, such as INT_MIN and INT_MAX.  This should be used instead of
\fB<limits.h>\fR because that header file is not available to kernel modules.

.SH REALTIME CONSIDERATIONS
.SS Userspace code
Certain functions are not available in userspace code.  This includes functions
that perform direct device access such as \fBrtapi_inb(3)\fR.

.SS Init/cleanup code
Certain functions may only be called from realtime init/cleanup code.
This includes functions that perform memory allocation, such as
\fBrtapi_shmem_new(3)\fR.

.SS Realtime code
Only a few functions may be called from realtime code.  This includes
functions that perform direct device access such as \fBrtapi_inb(3)\fR.
It excludes most Linux kernel APIs such as \fRdo_gettimeofday(3)\fR and
many rtapi APIs such as \fRrtapi_shmem_new(3)\fR.

.SS Simulator
For an RTAPI module to be buildable in the "sim" environment (fake realtime
system without special privileges), it must not use \fBany\fR linux kernel
APIs, and must not use the RTAPI APIs for direct device access such as
\fBrtapi_inb(3)\fR.  This automatically includes any hardware device drivers,
and also devices which use Linux kernel APIs to do things like create
special devices or entries in the \fB/proc\fR filesystem.

.SH RTAPI STATUS CODES
Except as noted in specific manual pages, RTAPI returns negative errno values
for errors, and nonnegative values for success.