The arbiter FSM defined in Section 6.8 (Figure 6.72) may cause device 3 to never get serviced

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The arbiter FSM defined in Section 6.8 (Figure 6.72) may cause device 3 to never get serviced if devices 1 and 2 continuously keep raising requests, so that in the Idle state it always happens that either device 1 or device 2 has an outstanding request. Modify the proposed FSM to ensure that device 3 will get serviced, such that if it raises a request, the devices 1 and 2 will be serviced only once before the device 3 is granted its request.


Data From Section6.8

FSM as an Arbiter Circuit
In this section we present the design of an FSM that is slightly more complex than the previous examples. The purpose of the machine is to control access by various devices to a shared resource in a given system. Only one device can use the resource at a time. Assume that all signals in the system can change values only following the positive edge of the clock signal. Each device provides one input to the FSM, called a request, and the FSM produces a separate output for each device, called a grant. Adevice indicates its need to use the resource by asserting its request signal. Whenever the shared resource is not already in use, the FSM considers all requests that are active. Based on a priority scheme, it selects one of the requesting devices and asserts its grant signal. When the device is finished using the resource, it deasserts its request signal.



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