Example From UVA ADEPTBus Resolution Function

• The token status priority used in the Protocol Bus Resolution function is illustrated below :

  • Note that the positions of the four arrows represent the four states in which the Protocol token inputs may be
  • For each of the four input conditions the token with the status at the head of the arrow is selected
  • Note that the cycle indicated by the illustration also shows the order of the status at the output of Protocol

Released

Removed

Present

Acked

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This slide illustrates the priority implemented in the Bus Resolution Function Protocol. The simplest case to consider (and the only one that will be used in the following example) is for a point-to-point connection in which one element serves as the token source and the other serves as the token sink. In this case, the status of the output token for the source will be either Present or Released, and the status of the output token for the sink will be either Acked or Removed.

The circle in the slide above serves two related purposes. First, note that at any one time, the arrows at the “corners” indicate the four possible states in which the two token drivers can be. For any of these four conditions, protocol will select the token that is at the head of the arrow.

The second purpose of the circle is to illustrate the sequence of token status conditions that will be seen by an observer on the signal connecting the two elements during a communication.