Dear readers,
My name is Sadashiv Balawad and I am working as Junior Software Engineer at Luxoft India. Luxoft gave me many opportunities to work on various projects, which inspired me to talk about the importance of multicore Real Time Operating Systems(Part-5)

Timed model with stopwatches
Timed fashions can be prolonged with stopwatches instead of clocks to model the temporal interruption of actions and subsequent resumption. Indeed, for timed automata(TA) and time Petri nets (TPN), time elapses at the equal pace for all gadget components. Hence they can't summary preemptive scheduling rules wherein the execution of a undertaking may be suspended and later resumed on the identical factor.
Several extensions of these models had been proposed to specific the suspension and resumption of actions with the aid of adding the stopwatch belief . Stopwatch automata is an extension that lets in modeling preemptive actual-time responsibilities. For TPNs, several extensions are proposed: Scheduling-TPN , Preemptive-TPN, and Time Petri nets with inhibitor hyperarcs (IHTPN) . The first extension is based on including two new attributes associated with locations: the allocation of the processor or aid and the concern of the modeled venture. The scheduling coverage considered is preemptive with constant priorities. Preemptive time Petri nets depend upon a aid assignment mechanism determining timer progress. IHTPN proposed in controls stopwatches related to transitions the usage of classical arcs and branch inhibitor hyperarcs. However, modeling a actual-time machine with preemptive scheduling the use of timed automata, specially in a multi-core context, isn't always usually easy. It requires an automaton per core, and the utility is described via an automata product. Extended Petri nets with stopwatches include a semantic of the behavior of real-time schedulers and can represent parallel or concurrent structures.

Scheduling studies based on timed models
The time verification of actual-time structures is composed in proving that the machine will always be capable of react in line with its time constraints. Timing validation is, therefore, a decision process that issues project scheduling sequences. Many scheduling studies are based on a representation by means of timed automata or TPNs .

Timed automata and scheduling
Several research use timed automata for the realtime gadget’s verification context and bear in mind scheduling evaluation. G. Behrmann et al. Advocate in a model of timed automata referred to as Priced Timed Automata (PTA). Its semantics is described by way of associating to every transition and vicinity a non-poor real valued value. Their evaluation is composed in seeking foremost offline scheduling with minimal fee the usage of UPPAAL’s model-checker. The authors in focuse on modeling multitasking applications to verify the worst time execution of the obligations the use of timed automata. The modeled applications taken into consideration non-preemptive responsibilities and ordinary service interrupts. The temporal and logical houses of those programs are proven in the UPPAAL model-checker. T. Zaharia and P. Haller present a framework for modeling and verification of embedded microsystems. The mini actual-time packages running underneath a multitasking kernel are defined thru networks of timed automata,
and the properties are specified in UPPAAL’s CTL subset. They focused on preemptive and non-preemptive scheduling duties with special priorities. Besides, supply code is automatically generated. The observe presented with the aid of the authors in proposes an approach to simulate preemptive scheduling the use of UPPAAL. They partner temporal diagrams with timed automata through mapping guidelines to check the time constraints and the impasse.

Time Petri nets and scheduling
Several studies proposed modeling with time Petri to verify complex actual-time systems and analyze schedulability. E. Grolleau and A. Choquet-Geniet present in the modeling of complicated systems with concurrent actions using colored PNs [61]. Their works, however, do not recall on-line schedulers,
and the PN generates an offline collection to execute. The work proposed by means of the authors in [60] shows a formal verification technique for actual-time structures with a preemptive scheduling policy, including Fixed Priority and Earliest Deadline First, with the possibility to use Round-Robin for responsibilities with the equal precedence. The modeling is done with scheduling time Petri nets and additionally lets in the verification of temporal homes for other scheduling regulations. Dianxiang et al. Examine in the scheduling of actual-time
systems the use of time Petri nets. Behavioral houses are separated from temporal properties at some point of verification. Behavioral specifications are verified through reachability righties, and temporal evaluation is conducted primarily based on absolute and relative trigger domains

Formal methods for operating systems verification
Formal verification of real-time working systems is beneficial to guarantee the perfectness of the gadget and to offer proof that the device is properly carried out. This is viable nowadays thanks to several equipment which have been developed in current years.
Several works had been finished on this context that we mention in the following. The list is not exhaustive, and different studies not mentioned in our work can also exist. Some are based totally on formal methods to affirm the same targets as the ones we've for verifying running structures compliant with OSEK/VDX and AUTOSAR requirements. Among the research, some do now not awareness on temporal verification whilst checking the OS and consider other factors of correction, such as the absence of deadlock or compliance with requirements. Other research works are extra interested by verifying temporal residences and schedulability evaluation thinking about the RTOS.

Deductive methods for operating systems verification
Existing formal techniques have been applied in some of studies research for working gadget software the usage of deductive techniques. The authors in [62–66] use evidence assistants to verify officially a real time operating machine. M. Hohmuth and H. Tews in [62] advocate a verification assignment of the L4 well matched Fiasco microkernel. The verification of the C++ resources of Fiasco is executed through the general-purpose theorem prover PVS. Their technique handles kind correctness and protection proof. The verification of seL4 microkernel in is carried out inner Isabelle/HOL. A entire verification method is executed independently of the application, from the high-degree specification of the kernel conduct to its secure execution.
Their evidence, however, is constrained to the validation of assumptions about the right functioning of the hardware and compiler. In , the Coq proof assistant is applied to the
formalized specification description of FreeRTOS - to affirm the correctness of significant homes expressed in Separation Logic. In, authors implemented an Earliest Deadline First (EDF) actual-time scheduling policy in seL4 microkernel and provided the
time control and periodic project model. Fengwei et al.recommend a verificationframework for preemptive operating gadget kernels. The framework allows the definition of the version by using a specification language and its verification by using program common sense. All proofs are in Coq, and the verification of the useful correctness of the kernel is done. Gu et al. [66] develop a certified concurrent OS kernel mC2 using CertiKOS and Coq proof assistant. They affirm its correctness and machine-call specification.

Thank you