Intel
®
81341 and 81342 I/O Processors
December 2007
Developer’s Manual
Order Number: 315037-002US
503
Application DMA Unit—Intel
®
81341 and 81342
5.7.7
P+Q Zero Result Buffer Check
The ADMA can be used to verify check values for P+Q RAID-6 implementations. As with
P+Q operations, descriptors are used to specify the memory blocks on which the ADMA
performs the P+Q Zero Result Buffer Check.
illustrates a P+Q
Zero Result Buffer Check performed by the ADMA. After processing all source data and
depending on the setting of the Status Write Back Enable in the ADCR, the ADMA either
updates the P Result Buffer Not Zero, Q Result Buffer Not Zero, and Transfer Complete
bits of the fourth word of the descriptor (ABCR) or signals an interrupt to the Intel
XScale
®
processor and suspend ADMA operation.
This operation can perform a consistency verification of the P and Q check data blocks
associated with up to 14 data blocks. Even though there are 16 Source Addresses
available, the next to last source address, and the last source address are reserved for
the associated P and Q check data blocks upon which the consistency verification is
performed. For example, in
, five source addresses are
programmed into the ADCR where SAR0-SAR2 represent three data blocks, SAR3
represents the P check data block, and SAR4 represents the Q check data block.
Note:
By setting the ‘P Transfer Disable’ bit in the ADCRx, the user may disable the Zero
Result Buffer Check of P while performing the Zero Result Buffer Check on Q.
Note:
The valid minimum number of sources to use in order to perform a P+Q Zero Result
Buffer Check is four data blocks. The four sources include the two source data blocks,
the P data block, and the Q data block.