Linear Descriptor Use Case

Zynq UltraScale+ Device Technical Reference Manual (UG1085)

Document ID
UG1085
Release Date
2022-09-15
Revision
2.3 English

In the linear descriptor use case mode, BDs are stored in a linear array. In This Figure, the first block shows the linear descriptor mode. This can be considered as one 4K page. Each descriptor is 128 bits and the DMA channel can fetch 256 bits on every descriptor read. This allows the DMA to fetch two descriptors in a single AXI read and reduces the number of descriptor fetches. Further details are shown in Table: Buffer Descriptor Format in Linear Descriptor Mode.

Each descriptor is 128 bits wide

Each descriptor must be 128-bit aligned

The descriptor element type is always 0 (in linear descriptor mode).

Table 19-1:      Buffer Descriptor Format in Linear Descriptor Mode

ADDR LSB
[31:0]

WORD0

RSVD
[31:12]

ADDR MSB
[11:0]

WORD1

RSVD
[31:29]

SIZE
[29:0]

WORD2

RSVD
[31:5]

CNTL
[4:0]

WORD3