Scalable Scatter-Gather DMA Intel® FPGA IP User Guide

ID 823097
Date 7/08/2024
Public

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Document Table of Contents

3.8.1. Link Descriptor

Table 10.  Link Descriptor Format
Offset Byte Lanes
3 2 1 0
0x00 DescrIDX Control

FormatField[7:0]

0b00xx_xx01

0x04 Reserved. Set to 0.
0x08 NextBlockAddress[31:0]
0x0C NextBlockAddress[63:32]
0x10-0x1C Reserved. Set to 0.
Table 11.  Link Descriptor — Field Description
Field Description
DescrIDX

Unique Identifier for each descriptor. This value is updated to the following value:

  • Q_EXTRACT_POINTER register when a descriptor data transfer is complete.
Note: First descriptor DESC_IDX value is 1, not 0.
Control The control field in the Link descriptor block.
NextBlockAddress

The address of the next 4kB page/descriptor block in host memory containing the descriptors.

Note: If there is only one 4kB page/descriptor block is allocated, the NextBlockAddress values must be configured to the values as defined in Q_START_ADDR_L & Q_START_ADDR_H CSR registers.

For both DMA PCIe mode & DMA SoC mode: The NextBlockAddress[1:0] must be set to zero for DWord aligned addressing. This is also applicable to the Q_START_ADDR_L[1:0] as well.

In addition, for DMA SoC mode:

The NextBlockAddress and Q_START_ADDR_* from Device Port CSR configured by software must be aligned to the HOST_DWD boundary. For example, both NextBlockAddress and Q_START_ADDR_* must be aligned to 32 bytes boundary for HOST_DWD = 256.

Table 12.  Link Descriptor — Control Field
Bit Field Description
6:0 Reserved Set to 0.
7 DescValid

If set, indicate the current link descriptor content is valid.

Notes: This bit must set to high always by software.