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  1. #1
    chanakya
    Guest
    What is PRD?(Physical Region Descriptor)
    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.

  2. #2
    vikrant
    Guest
    Physical Region Descriptor
    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.

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