MSC8144E Reference Manual, Rev. 3
17-12
Freescale
Semiconductor
RapidIO Interface Dedicated DMA Controller
17.2.4
DMA Descriptors
The DMA engine recognizes list descriptors and link descriptors. List descriptors connect lists of
link descriptors. Link descriptors describe the DMA activity that is to take place. DMA
descriptors are built in either local or remote memory and are connected by the next descriptor
fields. Only link descriptors contain information for the DMA controller to transfer data.
Software must ensure that each descriptor is 32-byte aligned. The last link descriptor in the last
list in memory sets the EOLND bit in the next link descriptor; the next list descriptor fields
indicating that these are the last descriptors in memory. Software initializes the current list
descriptor address register to point to the first list descriptor in memory. The DMA controller
traverses through the descriptor lists until the last link descriptor is met. For each link descriptor
in the chain, the DMA controller starts a new DMA transfer with the control parameters specified
by that descriptor. Link and list descriptor fetches always snoop the local memory space.
Note:
Software must ensure that each descriptor is aligned on a 32-byte boundary.
The last link descriptor in the last list in memory sets NLNDARn[EOLND] in the next link
descriptor and NLSDARn[EOLSD] in the next list descriptor fields indicating that these are the
last descriptors in memory. Software initializes the current list descriptor address register to point
to the first list descriptor in memory. The DMA controller traverses through the descriptor lists
until the last link descriptor is met as shown in. For each link descriptor in the chain, the DMA
controller starts a new DMA transfer with the control parameters specified by that descriptor.
Table 17-3 summarizes the DMA list descriptors.
Table 17-4 summarizes the DMA link descriptors.
Table 17-3. List DMA Descriptor Summary
Descriptor Field
Description
Next list
descriptor
extended address
Points to the next list descriptor in memory. After the DMA controller reads the descriptor from memory,
this field is loaded into the next list descriptor extended address registers.
Next list
descriptor
address
Points to the next list descriptor in memory. After the DMA controller reads the descriptor from memory,
this field is loaded into the next list descriptor address registers.
First link
descriptor
extended address
Points to the first link descriptor in memory for this list. After the DMA controller reads the descriptor
from memory, this field is loaded into the current link descriptor extended address registers.
First link
descriptor
address
Points to the first link descriptor in memory for this list. After the DMA controller reads the descriptor
from memory, this field is loaded into the current link descriptor address registers.
Source stride
Contains the stride information used for the data source if striding is enabled for a link in the list
Destination stride
Contains the stride information used for the data destination if striding is enabled for a link in the list
Summary of Contents for MSC8144E
Page 1: ...MSC8144E Reference Manual Quad Core Media Signal Processor MSC8144ERM Rev 3 July 2009 ...
Page 48: ...MSC8144E Reference Manual Rev 3 xlviii Freescale Semiconductor ...
Page 86: ...MSC8144E Reference Manual Rev 3 1 38 Freescale Semiconductor Overview ...
Page 168: ...MSC8144E Reference Manual Rev 3 3 60 Freescale Semiconductor External Signals ...
Page 242: ...MSC8144E Reference Manual Rev 3 5 26 Freescale Semiconductor Reset ...
Page 314: ...MSC8144E Reference Manual Rev 3 8 24 Freescale Semiconductor General Configuration Registers ...
Page 414: ...MSC8144E Reference Manual Rev 3 10 14 Freescale Semiconductor MSC8144E SC3400 DSP Subsystem ...
Page 452: ...MSC8144E Reference Manual Rev 3 11 38 Freescale Semiconductor Internal Memory Subsystem ...
Page 520: ...MSC8144E Reference Manual Rev 3 12 68 Freescale Semiconductor DDR SDRAM Memory Controller ...
Page 1070: ...MSC8144E Reference Manual Rev 3 21 28 Freescale Semiconductor Timers ...