PCIe BARs Tab - 2.0 English - PG344

Versal Adaptive SoC DMA and Bridge Subsystem for PCI Express Product Guide (PG344)
Document ID
PG344
Release Date
2024-11-22
Version
2.0 English

The PCIe BARs tab is shown in the following figure.

Figure 1. PCIe BARs Tab
Base Address Register Overview
In Endpoint configuration, the core supports up to six 32-bit BARs or three 64-bit BARs, and the Expansion read-only memory (ROM) BAR. BARs can be one of two sizes:
32-bit BARs
The address space can be as small as 128 B or as large as 2 GB.
64-bit BARs
The address space can be as small as 128 B or as large as 8 Exabytes.

For PCIe to AXI4-Lite Master interface, when 32-bit BAR options is selected, the address space can be from 128 B to 2 GB. When 64-bit BAR option is selected, the address space can be from 128 B to 4 GB.

For PCIe to DMA bypass interface, when 32-bit BAR option is selected, the address space can be from 128 B to 2 GB. When 64-bit BAR option is selected, the address space can be from 128 B to 8 ExaBytes.

All BAR registers share these options.

Important: The DMA requires a large amount of space to support functions and queues. By default, 64-bit BAR space is selected for the DMA BAR. This applies for PF and VF bars. You must calculate your design needs first before selecting between 64-bit and 32-bit BAR space.

BAR selections are configurable. By default DMA is at BAR 0 (64 bit), AXI4-Lite Master is at BAR 2 (64 bit). These selections can be changed according to user needs.

BAR
Click the checkbox to enable the BAR. Deselect the checkbox to disable the BAR.
Type
Select from DMA (by default in BAR0), AXI Lite Master (by default in BAR1, if enabled), or AXI Bridge Master (by default in BAR2, if enabled). All other BARs, you can select between AXI List Master and AXI Bridge Master. Expansion ROM can be enabled by selecting BAR6

For 64-bit BAR (default selection), DMA (by default in BAR0), AXI4-Lite Master (by default in BAR2, if enabled), and AXI Bridge Master (by default  in BAR4, if enabled). Expansion ROM can be enabled by selection BAR6.

DMA
DMA by default is assigned to BAR0 space and for all PFs. DMA option can be selected in any available BAR (only one BAR can have DMA option). If you select DMA Mailbox Management rather than DMA; however, DMA Mailbox Management does not allow you to perform any DMA operations. After selecting the DMA Mailbox Management option, the host has access to the extended Mailbox space. For details about this space, see the QDMA_PF_MAILBOX (0x22400) register space.
AXI Lite Master
Select the AXI4-Lite Master interface option for any BAR space. The Size, scale and address translation are configurable.
AXI Bridge Master
Select the AXI Bridge Master interface option for any BAR space. The Size, scale and address translation are configurable.
Expansion ROM
When enabled, this space is accessible on the AXI4-Lite Master. This is a read-only space. The size, scale, and address translation are configurable.
Size
The available Size range depends on the 32-bit or 64-bit bar selected. The DMA requires 256 KB of space, which is the fixed default selection. Other BAR size selections are available, but must be specified.
Scale
Select between Byte, Kilobytes and Megabytes.
Value
The value assigned to the BAR based on the current selections.
Note: For best results, disable unused base address registers to conserve system resources. A base address register is disabled by deselecting unused BARs in the Customize IP dialog box.