F-Tile Avalon® Streaming Intel® FPGA IP for PCI Express* User Guide

ID 683140
Date 10/22/2021
Public

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7.3.3. Configuration of Root Port and Endpoint

Before you issue transactions to the Endpoint, you must configure the Root Port and Endpoint Configuration Space registers.

The ebfm_cfg_rp_ep procedure in altpcietb_g3bfm_configure.v executes the following steps to initialize the Configuration Space:
  1. Sets the Root Port Configuration Space to enable the Root Port to send transactions on the PCI Express link.
  2. Sets the Root Port and Endpoint PCI Express Capability Device Control registers as follows:
    1. Disables Error Reporting in both the Root Port and Endpoint. The BFM does not have error handling capability.
    2. Enables Relaxed Ordering in both Root Port and Endpoint.
    3. Enables Extended Tags for the Endpoint if the Endpoint has that capability.
    4. Disables Phantom Functions, Aux Power PM, and No Snoop in both the Root Port and Endpoint.
    5. Sets the Max Payload Size to the value that the Endpoint supports because the Root Port supports the maximum payload size.
    6. Sets the Root Port Max Read Request Size to 4 KB because the example Endpoint design supports breaking the read into as many completions as necessary.
    7. Sets the Endpoint Max Read Request Size equal to the Max Payload Size because the Root Port does not support breaking the read request into multiple completions.
  3. Assigns values to all the Endpoint BAR registers. The BAR addresses are assigned by the algorithm outlined below.
    1. I/O BARs are assigned smallest to largest starting just above the ending address of the BFM shared memory in I/O space and continuing as needed throughout a full 32-bit I/O space.
    2. The 32-bit non-prefetchable memory BARs are assigned smallest to largest, starting just above the ending address of the BFM shared memory in memory space and continuing as needed throughout a full 32-bit memory space.
    3. The value of the addr_map_4GB_limit input to the ebfm_cfg_rp_ep procedure controls the assignment of the 32-bit prefetchable and 64-bit prefetchable memory BARS. The default value of the addr_map_4GB_limit is 0.

      If the addr_map_4GB_limit input to the ebfm_cfg_rp_ep procedure is set to 0, then the ebfm_cfg_rp_ep procedure assigns the 32‑bit prefetchable memory BARs largest to smallest, starting at the top of 32-bit memory space and continuing as needed down to the ending address of the last 32-bit non-prefetchable BAR.

      However, if the addr_map_4GB_limit input is set to 1, the address map is limited to 4 GB. The ebfm_cfg_rp_ep procedure assigns 32-bit and 64-bit prefetchable memory BARs largest to smallest, starting at the top of the 32-bit memory space and continuing as needed down to the ending address of the last 32-bit non-prefetchable BAR.

    4. If the addr_map_4GB_limit input to the ebfm_cfg_rp_ep procedure is set to 0, then the ebfm_cfg_rp_ep procedure assigns the 64-bit prefetchable memory BARs smallest to largest starting at the 4 GB address assigning memory ascending above the 4 GB limit throughout the full 64-bit memory space.

      If the addr_map_4 GB_limit input to the ebfm_cfg_rp_ep procedure is set to 1, the ebfm_cfg_rp_ep procedure assigns the 32-bit and the 64-bit prefetchable memory BARs largest to smallest starting at the 4 GB address and assigning memory by descending below the 4 GB address to memory addresses as needed down to the ending address of the last 32-bit non-prefetchable BAR.

      The above algorithm cannot always assign values to all BARs when there are a few very large (1 GB or greater) 32-bit BARs. Although assigning addresses to all BARs may be possible, a more complex algorithm would be required to effectively assign these addresses. However, such a configuration is unlikely to be useful in real systems. If the procedure is unable to assign the BARs, it displays an error message and stops the simulation.

  4. Based on the above BAR assignments, the ebfm_cfg_rp_ep procedure assigns the Root Port Configuration Space address windows to encompass the valid BAR address ranges.
  5. The ebfm_cfg_rp_ep procedure enables master transactions, memory address decoding, and I/O address decoding in the Endpoint PCIe* control register.

The ebfm_cfg_rp_ep procedure also sets up a bar_table data structure in BFM shared memory that lists the sizes and assigned addresses of all Endpoint BARs. This area of BFM shared memory is write-protected. Consequently, application logic write accesses to this area cause a fatal simulation error.

BFM procedure calls to generate full PCIe* addresses for read and write requests to particular offsets from a BAR use this data structure. This procedure allows the testbench code that accesses the Endpoint application logic to use offsets from a BAR and avoid tracking specific addresses assigned to the BAR. The following table shows how to use those offsets.

Table 104.  BAR Table Structure

Offset (Bytes)

Description

+0

PCI Express address in BAR0

+4

PCI Express address in BAR1

+8

PCI Express address in BAR2

+12

PCI Express address in BAR3

+16

PCI Express address in BAR4

+20

PCI Express address in BAR5

+24

PCI Express address in Expansion ROM BAR

+28

Reserved

+32

BAR0 read back value after being written with all 1’s (used to compute size)

+36

BAR1 read back value after being written with all 1’s

+40

BAR2 read back value after being written with all 1’s

+44

BAR3 read back value after being written with all 1’s

+48

BAR4 read back value after being written with all 1’s

+52

BAR5 read back value after being written with all 1’s

+56

Expansion ROM BAR read back value after being written with all 1’s

+60

Reserved

The configuration routine does not configure any advanced PCI Express capabilities such as the AER capability.

Besides the ebfm_cfg_rp_ep procedure in altpcietb_bfm_rp_gen3_x8.sv, routines to read and write Endpoint Configuration Space registers directly are available in the Verilog HDL include file. After the ebfm_cfg_rp_ep procedure runs, the PCI Express I/O and Memory Spaces have the layout shown in the following three figures. The memory space layout depends on the value of the addr_map_4GB_limit input parameter. The following figure shows the resulting memory space map when the addr_map_4GB_limit is 1.

Figure 67. Memory Space Layout—4 GB Limit

The following figure shows the resulting memory space map when the addr_map_4GB_limit is 0.

Figure 68. Memory Space Layout—No Limit

The following figure shows the I/O address space.

Figure 69. I/O Address Space

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