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

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

2.6.2.2.2. Pipelined Avalon® -MM Interfaces

Pipelined read transfers allow a pipelined master interface to start multiple read transfers in succession without waiting for prior transfers to complete. Pipelined transfers allow master-slave pairs to achieve higher throughput, even though the slave port may require one or more cycles of latency to return data for each transfer.

In many systems, read throughput becomes inadequate if simple reads are used and pipelined transfers can increase throughput. If you define a component with a fixed read latency, Platform Designer automatically provides the pipelining logic necessary to support pipelined reads. You can use fixed latency pipelining as the default design starting point for slave interfaces. If your slave interface has a variable latency response time, use the readdatavalid signal to indicate when valid data is available. The interconnect implements read response FIFO buffering to handle the maximum number of pending read requests.

To use components that support pipelined read transfers, and to use a pipelined system interconnect efficiently, your system must contain pipelined masters. You can use pipelined masters as the default starting point for new master components. Use the readdatavalid signal for these master interfaces.

Because master and slaves sometimes have mismatched pipeline latency, the interconnect contains logic to reconcile the differences.

Table 21.  Pipeline Latency in a Master-Slave Pair
Master Slave Pipeline Management Logic Structure
No pipeline No pipeline Platform Designer interconnect does not instantiate logic to handle pipeline latency.
No pipeline Pipelined with fixed or variable latency Platform Designer interconnect forces the master to wait through any slave-side latency cycles. This master-slave pair gains no benefits from pipelining, because the master waits for each transfer to complete before beginning a new transfer. However, while the master is waiting, the slave can accept transfers from a different master.
Pipelined No pipeline Platform Designer interconnect carries out the transfer as if neither master nor slave were pipelined, causing the master to wait until the slave returns data. An example of a non-pipeline slave is an asynchronous off-chip interface.
Pipelined Pipelined with fixed latency Platform Designer interconnect allows the master to capture data at the exact clock cycle when data from the slave is valid, to enable maximum throughput. An example of a fixed latency slave is an on-chip memory.
Pipelined Pipelined with variable latency The slave asserts a signal when its readdata is valid, and the master captures the data. The master-slave pair can achieve maximum throughput if the slave has variable latency. Examples of variable latency slaves include SDRAM and FIFO memories.