Intel
®
81341 and 81342—Application DMA Unit
Intel
®
81341 and 81342 I/O Processors
Developer’s Manual
December 2007
480
Order Number: 315037-002US
5.4
ADMA Descriptor Processing
To perform an XOR-transfer, a series of chain descriptors can be built in local memory
to XOR multiple blocks of source data resident in local memory. The XOR-ed result is
then stored back to either Host or local memory. An application can build multiple chain
descriptors to XOR many blocks of data which have different source addresses within
the local or Host memory.
When multiple chain descriptors are built in local or SRAM memory, the application can
link each of these chain descriptors using the Next Descriptor Address in the chain
descriptor. This address logically links the chain descriptors together. This allows the
application to build a list of transfers which may not require the processor until all
shows an example of a linked-list of transfers
specified in external memory.
Figure 53. Chaining Operation
Next Descriptor Address (NDA)
Descriptor Address Register
ADMA Control Register
Linked Descriptors In Local Memory
Buffer Transfers
First Chain
Descriptor
Operation
End of Chain
(Null Value Detected)
Descriptor Control (DC)
Next Descriptor Address (NDA)
Descriptor Control (DC)
Next Descriptor Address (NDA)
...
Second Chain
Descriptor
Operation
Nth Chain
Descriptor
Operation
Byte Count (BC)
Byte Count (BC)
Byte Count (BC)
Descriptor Control (DC)
B6224-01
Note: Since the end of a chain descriptor is indicated using a NULL
pointer, software should not place descriptors at physical address 0H.