Need info about RTC and Real-Time System

[arbalez]

RTC and Real-Time System

can i make my embedded system "real-time" with the inclusion of real-time clock? how can it be done? please shed some light for me on this. thanx.

 

[IanP]

Re: RTC and Real-Time System

First, you have to ask yourself what is a real-time sytem and then you can answer the following question:
What makes an OS a RTOS?

1. A RTOS (Real-Time Operating System) has to be multi-threaded and preemptible.
2. The notion of thread priority has to exist as there is for the moment no deadline driven OS.
3. The OS has to support predictable thread synchronisation mechanisms
4. A system of priority inheritance has to exist
5. OS Behaviour should be known
So the following figures should be clearly given by the RTOS manufacturer:
1. the interrupt latency (i.e. time from interrupt to task run) : this has to be compatible with application requirements and has to be predictable. This value depends on the number of simultaneous pending interrupts.
2. for every system call, the maximum time it takes. It should be predictable and independent from the number of objects in the system;
3. the maximum time the OS and drivers mask the interrupts.
The following points should also be known by the developer:
1. System Interrupt Levels.
2. Device driver IRQ Levels, maximum time they take, etc.

In this context adding RTC IC to a system does not make it "real-time". A microcontroller can count time and issue interrupts without external RTC. RTC gives you just the current time (and/or date) orientation.
More interesting oppinins on real-time you can find here:
**broken link removed**
Regards,
IanP