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OS X - Development and Darwin Discussion and questions about development for Mac OS X.

What is PRD?(Physical Region Descriptor)


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chanakya
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hi
i am a software trainee engineer who is learning the basics about writing device drivers. during this process i have encountered a problem and i m not able to understand the concept of PRD. so any help in this respect is appreciated.
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vikrant
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The physical memory region to be transferred is described by a Physical Region Descriptor (PRD). The
data transfer will proceed until all regions described by the PRDs in the table have been transferred.
Each Physical Region Descriptor entry is 8 bytes in length. The first 4 bytes specify the byte address of a
physical memory region. The next two bytes specify the count of the region in bytes (64K byte limit per
region). A value of zero in these two bytes indicates 64K. Bit 7 of the last byte indicates the end of the
table; bus master operation terminates when the last descriptor has been retired.
byte 3 byte 2 byte 1 byte 0
Memory Region Physical Base Address [31:1] Dword 0
Dword 1 EOT reserved Byte Count [15:1]
Memory Region 0
0

Quote:
Originally Posted by chanakya
hi
i am a software trainee engineer who is learning the basics about writing device drivers. during this process i have encountered a problem and i m not able to understand the concept of PRD. so any help in this respect is appreciated.
QUOTE Thanks

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