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

ID 683609
Date 10/04/2021
Public

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4.6.2.1. Differences Between Arbitration Shares and Bursts

The following three key characteristics distinguish arbitration shares and bursts:

  • Arbitration Lock
  • Sequential Addressing
  • Burst Adapters

Arbitration Lock

When a host posts a burst transfer, the arbitration is locked for that host; consequently, the bursting host should be capable of sustaining transfers for the duration of the locked period. If, after the fourth write, the host deasserts the write signal ( Avalon® memory mapped write or AXI wvalid) for fifty cycles, all other hosts continue to wait for access during this stalled period.

To avoid wasted bandwidth, your host designs should wait until a full burst transfer is ready before requesting access to an agent device. Alternatively, you can avoid wasted bandwidth by posting burstcounts equal to the amount of data that is ready. For example, if you create a custom bursting write host with a maximum burstcount of eight, but only three words of data are ready, you can present a burstcount of three. This strategy does not result in optimal use of the system band width if the agent is capable of handling a larger burst; however, this strategy prevents stalling and allows access for other hosts in the system.

Sequential Addressing

An Avalon® memory mapped burst transfer includes a base address and a burstcount, which represents the number of words of data that are transferred, starting from the base address and incrementing sequentially. Burst transfers are common for processors, DMAs, and buffer processing accelerators; however, sometimes a host must access non-sequential addresses. Consequently, a bursting host must set the burstcount to the number of sequential addresses, and then reset the burstcount for the next location.

The arbitration share algorithm has no restrictions on addresses; therefore, your custom host can update the address it presents to the interconnect for every read or write transaction.

Burst Adapters

Platform Designer allows you to create systems that mix bursting and non-bursting host and agent interfaces. This design strategy allows you to connect bursting host and agent interfaces that support different maximum burst lengths, with Platform Designer generating burst adapters when appropriate.

Platform Designer inserts a burst adapter whenever a host interface burst length exceeds the burst length of the agent interface, or if the host issues a burst type that the agent cannot support. For example, if you connect an AXI master to an Avalon® agent, a burst adapter is inserted. Platform Designer assigns non-bursting hosts and agent interfaces a burst length of one. The burst adapter divides long bursts into shorter bursts. As a result, the burst adapter adds logic to the address and burstcount paths between the host and agent interfaces.