- •Introduction
- •Applications of Real-Time Systems
- •Voltage
- •Figure 7: Conversion of an Analog Signal to a 16 bit Binary Number
- •Figure 11: Schematic Representation of tmr
- •It is relatively simple to design a hardware equipment to be fault-tolerant. The following are two methods that are popularly used to achieve hardware fault-tolerance:
- •Software Fault-Tolerance Techniques
- •Types of Real-Time Tasks
- •Timing Constraints
- •Events in a Real-Time System
- •Figure 16: Delay Constraint Between Two Events el and e2
- •Examples of Different Types of Timing Constraints
- •Figure 19: Classification of Timing Constraints
- •Real-Time Task Scheduling
- •Figure 1: Relative and Absolute Deadlines of a Task
- •Figure 2: Precedence Relation Among Tasks
- •Types of Real-Time Tasks and Their Characteristics
- •Classification of Real-Time Task Scheduling Algorithms
- •Figure 5: An Example Schedule Table for a Cyclic Scheduler
- •Figure 6: Major and Minor Cycles in a Cyclic Scheduler
- •Comparison of Cyclic with Table-Driven Scheduling
- •Hybrid Schedulers
- •Event-driven Scheduling
- •Is edf Really a Dynamic Priority Scheduling Algorithm?
- •Implementation of edf
- •Figure 10: Priority Assignment to Tasks in rma
- •We now illustrate the applicability of the rma schodulability criteria through a few examples.
- •Deadline Monotonic Algorithm (dma)
- •Handling Aperiodic and Sporadic Tasks
- •Dealing With Task Jitter
- •W Good real-time task scheduling algorithms ensure fairness to real-time tasks while scheduling.
- •State whether the following assertions are True or False. Write one or two sentences to justify your choice in each case.
- •Figure 2: Unbounded Priority Inversion
- •Highest Locker Protocol(hlp)
- •Priority Ceiling Protocol (pcp)
- •Comparison of Resource Sharing Protocols
- •Handling Task Dependencies
- •Fault-Tolerant Scheduling of Tasks
- •Clocks in Distributed Real-Time Systems
- •Clock Synchronization
- •Figure 1: Centralized synchronization system
- •Cn Slave clocks
- •Commercial Real-Time Operating Systems
- •Time Services
- •Clock Interrupt Processing
- •Providing High Clock Resolution
- •Figure 2: Use of a Watchdog Tinier
- •Unix as a Real-Time Operating System
- •In Unix, dynamic priority computations cause I/o intensive tasks to migrate to higher and higher priority levels, whereas cpu-intensive tasks are made to seek lower priority levels.
- •Host-Target Approach
- •Preemption Point Approach
- •Self-Host Systems
- •Windows As a Real-Time Operating System
- •Figure 9: Task Priorities in Windows nt
- •Open Software
- •Genesis of posix
- •Overview of posix
- •Real-Time posix Standard
- •Rt Linux
- •7.8 Windows ce
- •Benchmarking Real-Time Systems
- •Figure 13: Task Switching Time Among Equal Priority Tasks
- •Real-Time Communication
- •Figure 2: a Bus Architecture
- •Figure 4: Logical Ring in a Token Bus
- •Soft Real-Time Communication in a lan
- •Figure 6: Priority Arbitration Example
- •Figure 8: Problem in Virtual Time Protocol
- •Figure 9: Structure of a Token in ieee 802.5
- •Figure 10: Frames in the Window-based Protocol
- •Performance Comparison
- •A Basic Service Model
- •Traffic Characterization
- •Figure 16: Constant Bit-Rato Traffic
- •Routing Algorithms
- •Resource Reservation
- •Resource Reservation Protocol (rsvp)
- •Traffic Shaping and Policing
- •Traffic Distortion
- •Traffic Scheduling Disciplines
- •Figure 20: Packet Service in Jittor-edd
- •Differentiated Services
- •Functional Elements of DiffServ Architecture
- •Real Time Databases
- •Isolation: Transactions are executed concurrently as long as they do not interfere in each other’s computations.
- •Real-Time Databases
- •Real-Time Database Application Design Issues
- •Temporal Consistency
- •Concurrency Control in Real-Time Databases
- •It can bo shown that pcp is doadlock froo and single blocking. Rocolloct that single blocking moans that once a transaction starts executing after being blocked, it may not block again.
- •Speculative Concurrency Control
- •Comparison of Concurrency Control Protocols
- •Commercial Real-Time Databases
- •Figure 16: Uniform Priority Assignment to Tasks of Example 15
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Figure 16: Uniform Priority Assignment to Tasks of Example 15
This priority assignment scheme has been pictorially shown in Fig. 16.
1 Clock resolution denotes the time granularity provided by the system clock of a computer. Thus, the resolution of a system clock corresponds to the duration of time that elapses between two successive clock ticks.
1In fact,, in DOS there is only one mode of operation, i.e. kernel and user modes are indistinguishable.
1Interrupt Processing. In Windows NT, the priority level of interrupts is always higher than that of the user-level threads; including the threads of real-time class. When an interrupt occurs, the handler routine saves the machine’s state and makes the system execute an Interrupt Service Routine (ISR). Only very critical processing is performed in ISR and the bulk of the processing is done later at a lower priority in the form of a Deferred Procedure Call(DPC). DPCs for various interrupts are queued in the DPC queue in a FIFO manner. While this separation of ISR and DPC has the advantage of providing quick response to further interrupts, it has the disadvantage of maintaining all DPCs at the same priority values. A DPC can not be preempted by another DPC but can be preempted by an interrupt. DPCs are executed in FIFO order at a priority lower than the hardware interrupt priority but higher than the priority of the scheduler/dispatcher. It is not possible for a user-level thread to execute at a priority higher than that of ISRs or DPCs. Therefore, even ISRs and DPCs corresponding to very low priority tasks can preempt real-time processes. As a result, the potential blocking of real-time tasks due to DPCs can be large. For example, interrupts due to page faults generated by low priority tasks would get processed faster than real-time processes. Also, ISRs and DPCs generated due to key board and mouse interactions would operate at higher priority levels compared to real-time tasks. Therefore
1Figure 21: Two Level Framing with T2 = 3 x T\ 29
1 The Default (DE) PHB is the common, best-effort forwarding available in today’s Internet. IP packets marked for this service are sent into a network without adhering to any particular rules and the network will deliver as many of these packets as possible and as soon as possible but without any guarantees.
Assured Forwarding (AF) PHB is a means for a provider differentiated services domain to offer different levels of forwarding assurances for IP packets received from a customer differentiated services domain.
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