Rios

Abstract

RIOS (Riverside-Irvine Operating System) is a lightweight portable task scheduler written entirely in C. The scheduler consists of just a few dozens lines of code, intended to be understandable by students learning embedded systems programming. Non-preemptive and preemptive scheduler versions exist. Compared to the existing open-source solutions FreeRTOS and AtomThreads, RIOS on average has 95% fewer lines of total C code for a sample multitasking application, a 71% smaller executable, and 70% less scheduler time overhead. RIOS source code and examples are available for free at http://www.riosscheduler.org. RIOS is useful for education and as a stepping stone to understanding real-time operating system behavior. Additionally, RIOS is a sufficient real-time scheduling solution for various commercial applications.

An Effective Real-Time Dynamic Scheduling Approach for Periodic Tasks

“…Preemptive approach: where a task is blocked by a higher priority process and 2. Non preemptive approach: where the task completes its execution time even if a higher priority process has arrived [1], [2], [3]. A scheduling policy can be characterized by several factors which are summarized as follows: A.…”

“…A scheduling policy can be characterized by several factors which are summarized as follows: A. Do all processes meet their deadlines?, B. CPU Utilization: the percentage of the CPU being busy, C. Response time for every job and D. Fairness: which is dividing the CPU time equally among all available jobs [2], [3] and load balancing which is dividing the load equally among all processors/cores.…”

“…The higher request is the higher priority is. However, that priority does not change during run-time and that is why it is called static [3], [6], 2) Deadline Monotonic (DM): is a generalization version of rate monotonic. Their concepts are almost the same; however, the difference is that in deadline monotonic a priority assigned to each process is inversely proportional to its deadline.…”

“…Their concepts are almost the same; however, the difference is that in deadline monotonic a priority assigned to each process is inversely proportional to its deadline. So a process with shortest deadline gets highest priority and assigned first to the resources [3], [6], 3) Earliest Deadline First (EDF): a process with shortest deadline time gets its turn first since it has a highest priority among all other processes. This algorithm is considered optimal and can be used for both types of tasks (periodic and aperiodic) in uniprocessor environments and 4) Least Slack Time first (LST): where a task with smallest slack is chosen first and assigned to available resources for execution.…”

“…This algorithm is considered optimal and can be used for both types of tasks (periodic and aperiodic) in uniprocessor environments and 4) Least Slack Time first (LST): where a task with smallest slack is chosen first and assigned to available resources for execution. Slack is defined as the difference between the deadline (d) of any task with its remaining execution time (c r ) and current time (t) as depicted in figure 1 [2], [3], [4], [5]. which is an interval time between first creation of the process and its deadline; mathematically, it is d = D + r. In many cases, P and d are the same.…”