Altera IP Compiler for PCI Express - Manual (Page 249)

Chapter 15: Testbench and Design Example 15–17
Chaining DMA Design Example
August 2014 Altera Corporation IP Compiler for PCI Express User Guide
Chaining DMA Descriptor Tables
Table 15–10 describes the Chaining DMA descriptor table which is stored in the BFM
shared memory. It consists of a four-dword descriptor header and a contiguous list of
four-dword descriptors. The endpoint chaining DMA application accesses the
Chaining DMA descriptor table for two reasons:
■ To iteratively retrieve four-dword descriptors to start a DMA
■ To send update status to the RP, for example to record the number of descriptors
completed to the descriptor header
Each subsequent descriptor consists of a minimum of four dwords of data and
corresponds to one DMA transfer. (A dword equals 32 bits.)
1
Note that the chaining DMA descriptor table should not cross a 4 KByte boundary.
Table 15–10. Chaining DMA Descriptor Table
Byte Address Offset to
Base Source
Descriptor Type Description
0x0
Descriptor Header
Reserved
0x4 Reserved
0x8 Reserved
0xC
EPLAST - when enabled by the EPLAST_ENA bit
in the control register or descriptor, this location
records the number of the last descriptor
completed by the chaining DMA module.
0x10
Descriptor 0
Control fields, DMA length
0x14 Endpoint address
0x18 RC address upper dword
0x1C RC address lower dword
0x20
Descriptor 1
Control fields, DMA length
0x24 Endpoint address
0x28 RC address upper dword
0x2C RC address lower dword
. . .
0x ..0
Descriptor
Control fields, DMA length
0x ..4 Endpoint address
0x ..8 RC address upper dword
0x ..C RC address lower dword