V-Series Avalon-MM DMA Interface for PCIe Solutions User Guide

ID 683514
Date 7/31/2018
Public
Document Table of Contents

3.1. System Settings

Table 16.  System Settings for PCI Express

Parameter

Value

Description

Number of Lanes

x1, x2, ×4, ×8

Specifies the maximum number of lanes supported. Avalon-MM Interface with DMA does not support x1 configurations.

Lane Rate

Gen1 (2.5 Gbps)

Gen2 (2.5/5.0 Gbps)

Gen3 (2.5/5.0/8.0 Gbps) 

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

Application interface width 128-bit

256-bit

Specifies the width of the interface to the Application Layer. The following table indicates the possible combinations.
Application Interface Width Configuration Application Layer Clock Frequency
128 bits Gen1 x8 125 MHz
128 bits Gen2 x4 125 MHz
128 bits Gen2 x8 250 MHz
256 bits Gen2 x8 125 MHz
128 bits Gen3 x4 250 MHz
256 bits Gen3 x4 125 MHz
256 bits Gen3 x8 250 MHz

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 Stratix V Avalon-ST Interface for PCIe Solutions User Guide for more information about optimizing performance.

The Message window 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 )—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—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 for which 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 in which most of the PCIe traffic is generated by a DMA engine that is located in the endpoint application layer logic.
  • Balanced—configures 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 applications in which the received requests and received completions are roughly equal.

Reference clock frequency

100 MHz

125 MHz

The PCI Express Base Specification 3.0 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. For more information about Gen3 operation, refer to 4.3.8 Refclk Specifications for 8.0 GT/s in the specification.

For Gen3 operation, Altera recommends using a common reference clock (0 ppm) because when using separate reference clocks (non 0 ppm), the PCS occasionally must insert SKP symbols, potentially causes the PCIe link to go to recovery. Gen1 or Gen2 modes are not affected by this issue. Systems using the common reference clock (0 ppm) are not affected by this issue. The primary repercussion of this is a slight decrease in bandwidth. On Gen3 x8 systems, this bandwidth impact is negligible. If non 0 ppm mode is required, so that separate reference clocks are being used, please contact Altera for further information and guidance.

Instantiate internal descriptor controller

On/Off

When you turn this option on, the descriptor controller is included in the Avalon-MM bridge. When you turn this option off, the descriptor controller should be included as a separate external component. Turn this option on, if you plan to use the Altera-provided descriptor controller in your design. Turn this option off if you plan to modify or replace the descriptor controller logic in your design.
Enable Avalon-MM CRA Slave hard IP status port On/Off

Allows read and write access to bridge registers from the interconnect fabric using a specialized slave port. This option is required for Requester/Completer variants and optional for Completer Only variants. Enabling this option allows read and write access to bridge registers, except in the Completer-Only single dword variations.

Enable burst capabilities for RXM BAR2 port

On/Off

When you turn on this option, the BAR2 RX Avalon-MM masters is burst capable. If BAR2 is 32 bits and Burst capable, then BAR3 is not available for other use. If BAR2 is 64 bits, the BAR3 register holds the upper 32 bits of the address.
Enable configuration via the PCIe link On/Off 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
Use ATX PLL

On/Off

When you turn on this option, the Hard IP for PCI Express uses the ATX PLL instead of the CMU PLL. For other configurations, using the ATX PLL instead of the CMU PLL reduces the number of transceiver channels that are necessary. This option requires the use of the soft reset controller and does not support the CvP flow.

Enable Hard IP reset pulse at power-up when using the soft reset controller

On/Off

When you turn on this option, the soft reset controller generates a pulse at power up to reset the Hard IP. This pulse ensures that the Hard IP is reset after programming the device, regardless of the behavior of the dedicated PCI Express reset pin, perstn. This option is available for Gen2 and Gen3 designs that use a soft reset controller.

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