Intel® Quartus® Prime Standard Edition User Guide: Platform Designer

ID 683364
Date 12/15/2018
Public
Document Table of Contents

3.1.5.1.1. Fairness-Based Shares

In a fairness-based arbitration scheme, each master-to-slave connection provides a transfer share count. This count is a request for the arbiter to grant a specific number of transfers to this master before giving control to a different master. One share represents permission to perform one transfer.
Figure 89. Arbitration of Continuous Transfer Requests from Two MastersConsider a system with two masters connected to a single slave. Master 1 has its arbitration shares set to three, and Master 2 has its arbitration shares set to four. Master 1 and Master 2 continuously attempt to perform back-to-back transfers to the slave. The arbiter grants Master 1 access to the slave for three transfers, and then grants Master 2 access to the slave for four transfers. This cycle repeats indefinitely. The figure below describes the waveform for this scenario.
Figure 90. Arbitration of Two Masters with a Gap in Transfer RequestsIf a master stops requesting transfers before it exhausts its shares, it forfeits all its remaining shares, and the arbiter grants access to another requesting master. After completing one transfer, Master 2 stops requesting for one clock cycle. As a result, the arbiter grants access back to Master 1, which gets a replenished supply of shares.