Real Time Operating Systems
# Real Time OS
Systems whose correctness depends not only on logical aspects but also on the temporal aspects i.e. able to meet specific deadlines.
# Real Time Process
Notice that C is often impossible to determine except for small specific applications.
# Recurrent RTOS process
Usually executes some function or goes through a set of steps in a regular manner repeated over time. e.g. Collect data from sensors, execute control laws, send actuator commands
# Periodic RTOS Process
# Sporadic RTOS Process
# Real Time Process Scheduling
Classical scheduling algorithms will fail to schedule RTOS processes as they do not take into account the deadlines of the processes.
# Fixed priority scheduling
Priorities are fixed across instances of recurrent processes. Easy to implement with low time complexity. If all types of processes are known and small, a hash map is able to do this in constant time.
# Rate Monotonic Scheduler
Since the scheduler is based on periodic time, it still does not prioritise based on deadlines. P3 misses the deadline if it is <20,2,14>: less time to complete the process in first appearance.
# Deadline Monotonic Scheduler
A natural solution to RM scheduler:
# Dynamic Priority Scheduling
# Earliest Deadline First Scheduler
Priority is based on the instance level rather than the process level.
# Comparisons
# Practice Problems
a. False. Real time does not mean fast or very short time, but rather to guarantee response times within a pre-defined deadline in the worst case
b. True.
c. False. It is the host OS that does this. The guest OS interacts with the hypervisor and provides services to the applications running on it.
d. False. Hypervisor manages interactions between H/W and guest OS
e. True.
Yes:
Yes?
