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"A realtime system is one in which the correct operation of the system depends not only on the logical correctness of any computed result, but also on the time at which the result is delivered. A system in which all computed results must be delivered on time is a hard realtime (HRT) system. A system in which the computed results are sometimes allowed to be late is called a soft realtime (SRT) system." [Original source lost]
A true realtime OS is an HRT system; a system in which the designed-in capabilities of processor and OS are such that there is no case when the processor is in conflict by having to perform two tasks simultaneously. A "regular" O.S. could theoretically be an HRT system, but if the overhead in the system causes delay, or unexpected inputs must be delayed (held) in a buffer for processing, then the system has defaulted back to an SRT at best. Xp for example has tons of overhead which is necessary for advanced applications but is not necessary for a task-specific embedded controller.
A realtime system is necessary when there is no tolerance for fault or misstep and timing is critical. As an example, if a digitally controlled autopilot starts missing feedback values, and reads "old" data, uncontrolled oscillations could occur.
A realtime OS for a given system is any OS that is able to handle every command, input, or output, everytime, without failure, forever.
Widely asked Question.
Concept wise the working remains same.
Here the response time plays a important role.
RTOS reponse within a specified time for the tasks. But general OS cant be expected to reponse within the specified time.
Thats why we call it as "Real Time OS".
Real time means the acting at a specified time.
RTOS should be Robust and should be self healing because embedded systems cannot be rebooted as we do with out desktop PCs.
Lots of information is availabe regarding RTOS in this forum itself.
U can find excellent books on RTOS in this website itself.
Hi
The main different between the RTOS and OS is his name :RT(real-time)
this is the RTOS's target.
For this arm. the RTOS use a different method .
For example
1: preemptive, multi-priority scheduler.
2:flat memory,no page manger
3:use for RICS achitecture CPU.
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