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

ID 683609
Date 6/26/2023
Public

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6.1.5.1.1. Fairness-Based Shares

In a fairness-based arbitration scheme, each host-to-agent connection provides a transfer share count. This count is a request for the arbiter to grant a specific number of transfers to this host before giving control to a different host. One share represents permission to perform one transfer.
Figure 188. Arbitration of Continuous Transfer Requests from Two HostsConsider a system with two hosts connected to a single agent. Host 1 has its arbitration shares set to three, and Host 2 has its arbitration shares set to four. Host 1 and Host 2 continuously attempt to perform back-to-back transfers to the agent. The arbiter grants Host 1 access to the agent for three transfers, and then grants Host 2 access to the agent for four transfers. This cycle repeats indefinitely. The figure below describes the waveform for this scenario.
Figure 189. Arbitration of Two Hosts with a Gap in Transfer RequestsIf a host stops requesting transfers before it exhausts its shares, it forfeits all its remaining shares, and the arbiter grants access to another requesting host. After completing one transfer, Host 2 stops requesting for one clock cycle. As a result, the arbiter grants access back to Host 1, which gets a replenished supply of shares.