Consider an arbiter that uses the priority scheme described in Problem 7.13. Wha
ID: 1714881 • Letter: C
Question
Consider an arbiter that uses the priority scheme described in Problem 7.13. What
happens if one device requests service repeatedly. Compare the behavior of this arbiter to
one that uses a fixed-priority scheme.
Problem 7.13
7.13 [E] An arbiter controls access to a common resource. It uses a rotating-priority scheme
in responding to requests on lines R1 through R4. Initially, R1 has the highest priority
and R4 the lowest priority. After a request on one of the lines receives service, that line
drops to the lowest priority, and the next line in sequence becomes the highest-priority
line. For example, after R2 has been serviced, the priority order, starting with the highest,
becomes R3, R4, R1, R2. What will be the sequence of grants for the following sequence
of requests: R3, R1, R4, R2? Assume that the last three requests arrive while the first one
is being serviced.
Explanation / Answer
As can be seen in the priority order thr served line drops to lower priority; the grants order reverses. The first served line the grant in the end later on. the sequence will be as follow:
R2>R4>R1>R3