Intel
®
81341 and 81342—Application DMA Unit
Intel
®
81341 and 81342 I/O Processors
Developer’s Manual
December 2007
466
Order Number: 315037-002US
5.3
ADMA Descriptors
The ADMA operations are managed through the use of descriptors that are arranged in
local memory. These descriptors are fetched by the ADMA through pointers contained
in the descriptor (in other words, scatter/gather chain descriptors).
The Application DMA Unit implements the XOR algorithm and an XOR algorithm
combined with a Galois field multiply operation. It performs these algorithms on
multiple streams of source (incoming) data and stores the result back in 81341 and
81342 local memory or to the host I/O interface.
• The process of reading source data, executing the XOR algorithm, and storing the
XOR data is hereafter referred to as XOR-transfer.
• The process of performing two XOR-transfer operations in a single descriptor is
hereafter referred to as Dual-XOR-transferThe process of reading or writing data is
hereafter referred to as data transfer.
• The process of reading source data, performing a Galois field multiply on the source
data, then, executing the XOR algorithm, and storing the XOR data is hereafter
referred to as P+Q-transfer.
The source and destination addresses are specified through the chain descriptors
resident in 81341 and 81342 local memory.
There are four types of chain descriptors, Basic, Full, Dual XOR, and P+Q Update. Basic
chain descriptors consume 32 bytes of memory, Full chain descriptors consume 152
bytes of memory, while Dual XOR and P+Q Update chain descriptors consume 64 bytes
of memory.
illustrates the different functionality supported by the four
descriptor types.
Table 307. Basic and Full Chain Descriptor Functions Support
Type
Data
Transfer
CRC-32C
Acceleration
a
a. CRC-32C acceleration can be performed with/without a Data Transfer.
Memory Block
Fill
b
b. Memory Block Fill can not be combined with any other operation.
XOR Transfer (16 Sources)
Basic
Yes
Yes
Yes
No
Full
No
c
c. When the Source Selection field of the ADCR is programmed for more than a single source requiring a Full
Descriptor, then the ADMA performs either an XOR Transfer or a Zero Result Buffer Check operation.
No
No
Yes
P+Q
No
d
d. When the Source Selection field of the ADCR is programmed for more than a single source and the P+Q
functionality is enabled, then the ADMA performs either an XOR Transfer with the P+Q function applied to the
Source Data streams or a Zero Result Buffer Check operation.
No
No
Yes
Dual XOR
Supports Dual XOR Operation only
P+Q Update
Supports P+Q Update Transfer Operation only