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

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

A.4.5. PCI Express-to-Avalon-MM Downstream Write Requests

The PCI Express Avalon-MM bridge receives PCI Express write requests, it converts them to burst write requests before sending them to the interconnect fabric. For Endpoints, the bridge translates the PCI Express address to the Avalon‑MM address space based on the BAR hit information and on address translation table values configured during the IP core parameterization. For Root Ports, all requests are forwarded to a single RX Avalon‑MM master that drives them to the interconnect fabric. Malformed write packets are dropped, and therefore do not appear on the Avalon-MM interface.

For downstream write and read requests, if more than one byte enable is asserted, the byte lanes must be adjacent. In addition, the byte enables must be aligned to the size of the read or write request.

As an example, the following table lists the byte enables for 32-bit data.

Table 72.  Valid Byte Enable Configurations

Byte Enable Value

Description

4’b1111

Write full 32 bits

4’b0011

Write the lower 2 bytes

4’b1100

Write the upper 2 bytes

4’b0001

Write byte 0 only

4’b0010

Write byte 1 only

4’b0100

Write byte 2 only

4’b1000

Write byte 3 only

In burst mode, the Cyclone® V Hard IP for PCI Express supports only byte enable values that correspond to a contiguous data burst. For the 32‑bit data width example, valid values in the first data phase are 4’b1111, 4’b1110, 4’b1100, and 4’b1000, and valid values in the final data phase of the burst are 4’b1111, 4’b0111, 4’b0011, and 4’b0001. Intermediate data phases in the burst can only have byte enable value 4’b1111.

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