07-08-2012, 02:45 PM
Real Time Operating Systems Lectures
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Operating Systems
What does an operating system really do?
Manages computer system resources (processor, memory, I/O, etc.)
keeps track of status and owner of each resource
decides who gets resource
decides how long the resource can be in use
In systems that support concurrent execution of programs, it
resolves conflicts for resources
optimizes performance given multiple users
Think of it as the keeper of a single copy of a book that everyone in
this course needs to read
Tasks and Functions
A task is a process that repeats itself
Loop forever
Essential building block of real time software systems
A function is a procedure that is called. It runs, then exits and may
return a value. For example,
process_data();
int add_two_numbers(int x, int y);
Polled Loops
Simplest RT kernel
A single and repetitive instruction tests a flag that indicates whether or
not an event has occurred.
No intertask communication or scheduling needed. Only a single tasks
exists.
Excellent for handling high-speed data channels, especially when
events occur at widely spaced intervals and
processor is dedicated to handling the data channel
INTERRUPT-DRIVEN SYSTEMS
Interrupt Driven Software Examples
IFF receiver sees a threat and interrupts an aircraft mission computer to
sound a cockpit alarm
Inertial Navigation Unit data (Δ velocities in north/east/up coordinates) is
available at 32 Hz and interrupts the navigation software with new data
when it is ready
Sonar contact data interrupts signal processing software when new data is
available
Low altitude indicator triggers a fly-up command for a pilot