Arbitration and Priority

Arbitration means deciding who gets the bus when two or more devices request it. Priority is a means of specifying the relative importance of messages to be sent on the MCB. In this MCB implementation, the priority will be based on the priority of the calling task, and on whether this is a control or monitor request. All control requests get higher priority than monitor requests. This is done because control tasks are usually one-time requests, and because control messages need to be acted upon in a more timely fashion.

Example: Assume that we have 4 requests in the queue:

1

Control message with a calling task priority of 200

2

Control message with a calling task priority of 100

3

Monitor message with a calling task priority of 150

4

Monitor message with a calling task priority of 50

Then, The requests will be executed in the order 2, 1, 4, 3.