Cyclone® V Avalon® Memory Mapped (Avalon-MM) Interface for PCIe* Solutions User Guide

ID 683494
Date 3/19/2020
Public
Document Table of Contents

3.1. Avalon-MM System Settings

Table 9.  System Settings for PCI Express

Parameter

Value

Description

Number of Lanes

×1, ×2, ×4

Specifies the maximum number of lanes supported.

Lane Rate

Gen1 (2.5 Gbps)

Gen2 (2.5/5.0 Gbps)

Specifies the maximum data rate at which the link can operate.

Port type

Root Port

Native Endpoint

Specifies the port type. Altera recommends Native Endpoint for all new Endpoint designs. The Legacy Endpoint is not available for the Avalon‑MM Cyclone V Hard IP for PCI Express.

The Endpoint stores parameters in the Type 0 Configuration Space. The Root Port stores parameters in the Type 1 Configuration Space.

RX Buffer credit allocation -performance for received requests

Minimum

Low

Balanced

Determines the allocation of posted header credits, posted data credits, non-posted header credits, completion header credits, and completion data credits in the 16 KByte RX buffer. The settings allow you to adjust the credit allocation to optimize your system. The credit allocation for the selected setting displays in the message pane.

Refer to the Throughput Optimization chapter in the Cyclone V Avalon-ST Interface for PCIe Solutions User Guidefor more information about optimizing performance.

Refer to the Throughput Optimization chapter for more information about optimizing performance. The Flow Control chapter explains how the RX credit allocation and the Maximum payload RX Buffer credit allocation and the Maximum payload size that you choose affect the allocation of flow control credits. You can set the Maximum payload size parameter on the Device tab.

The Message window of the GUI dynamically updates the number of credits for Posted, Non‑Posted Headers and Data, and Completion Headers and Data as you change this selection.

  • Minimum RX Buffer credit allocation -performance for received requests )–This setting configures the minimum PCIe specification allowed for non-posted and posted request credits, leaving most of the RX Buffer space for received completion header and data. Select this option for variations where application logic generates many read requests and only infrequently receives single requests from the PCIe link.
  • Low–This setting configures a slightly larger amount of RX Buffer space for non-posted and posted request credits, but still dedicates most of the space for received completion header and data. Select this option for variations where application logic generates many read requests and infrequently receives small bursts of requests from the PCIe link. This option is recommended for typical endpoint applications where most of the PCIe traffic is generated by a DMA engine that is located in the endpoint application layer logic.
  • Balanced–This setting allocates approximately half the RX Buffer space to received requests and the other half of the RX Buffer space to received completions. Select this option for variations where the received requests and received completions are roughly equal.

Reference clock frequency

100 MHz

125 MHz

The PCI Express Base Specification requires a 100 MHz ±300 ppm reference clock. The 125 MHz reference clock is provided as a convenience for systems that include a 125 MHz clock source.

Use 62.5 MHz application clock

On/Off

This mode is only available only for Gen1 ×1.

Enable configuration via PCIe link

On/Off

When On, the Quartus® Prime software places the Endpoint in the location required for configuration via protocol (CvP). For more information about CvP, click the Configuration via Protocol (CvP) link below. CvP is not supported for Gen3 variants.

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