Real Time Application Interface

1. Real Time Application
Interface(RTAI)
Presented By
Debjyoti Basu(IT/2008/34)
Soumya Sarkar(IT/2008/14)

2. What is RTAI?
• Real-Time Application Interface (RTAI) is a
real-time Linux implementation
• It adds a small real-time kernel below the
standard Linux kernel.
• RTAI provides a large selection of inter-process
communication mechanisms and other
realtime services

3. Why RTAI ?
• Hard Real Time operating system may be small
and convenient but they do not provide basic
features like memory management,
networking etc.
• This problem was solved by Rtlinux which has
been used as a basis for many other real-time
Linux solutions.
• One of the solutions based on RTLinux is Real-
Time Application Interface (RTAI).

4. Architecture of RTAI
• RTAI treats the conventional Linux kernel as a
low-priority real-time task.
• There are interrupts originating from
processor and peripherals
• processor originated interrupts are still
handled by the standard Linux kernel but the
interrupts from the peripherals are handled by
RTAI’s Interrupt dispatcher.

5. Architecture of RTAI(contd..)
• The RTAI forwards the
interrupts to the
standard Linux kernel
handlers when there no
active real-time tasks
• The interrupt disabling
and enabling
instructions (cli()/sti()) in
Linux kernel are replaced
by macros that forward
the instructions to RTAI.

6. Hardware abstraction layer
• RTAI developers introduced
the concept of Real-Time
Hardware Abstraction Layer
(RTHAL).
• RTHAL is a structure installed
in the Linux kernel which
gathers the pointers to
relevant data.
• The purpose of RTHAL is to
minimize the number of
changes needed to make to
the kernel code.

7. Scheduling
• The scheduling units of RTAI are called tasks.
• There is always at least one task, namely the
Linux kernel which is run as a low-priority task.
• When real time tasks are added, the scheduler
gives them priority over the Linux kernel.
• The scheduler provides services which are
used in various real-time operating systems.

8. Interrupt Handling using RTAI
Interrupt Occurrence
RTAI Dispatcher
RT Int Handler
Linux Dispatcher
SRQ Dispatcher
Linux Intr Ret
Interupt Return
Return to Program Execution

9. Services provided by RTAI
• RTAI provides a variety of mechanisms for inter-
process communication
• RTAI include a memory management modules
which allows dynamic allocation of memory in
the real-time tasks
• RTAI provides pthreads module which
implements threads according to the POSIX
1003.1c standard.
• RTAI provides API(LXRT) for Real Time Application
Development

10. Conclusion
• Like Linux itself the RTAI software is a
community effort.
• Substantial research is going on to make this
software work in all platforms
• Open Source development methodology frees
this software from any patent restrictions

11. Any Question??