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macOS - Development and Darwin
What is PRD?(Physical Region Descriptor)
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<blockquote data-quote="vikrant" data-source="post: 44595"><p><strong>Physical Region Descriptor</strong></p><p></p><p>The physical memory region to be transferred is described by a Physical Region Descriptor (PRD). The</p><p>data transfer will proceed until all regions described by the PRDs in the table have been transferred.</p><p>Each Physical Region Descriptor entry is 8 bytes in length. The first 4 bytes specify the byte address of a</p><p>physical memory region. The next two bytes specify the count of the region in bytes (64K byte limit per</p><p>region). A value of zero in these two bytes indicates 64K. Bit 7 of the last byte indicates the end of the</p><p>table; bus master operation terminates when the last descriptor has been retired. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile :)" loading="lazy" data-shortname=":)" /> </p><p>byte 3 byte 2 byte 1 byte 0</p><p>Memory Region Physical Base Address [31:1] Dword 0</p><p>Dword 1 EOT reserved Byte Count [15:1]</p><p>Memory Region 0</p><p>0</p></blockquote><p></p>
[QUOTE="vikrant, post: 44595"] [b]Physical Region Descriptor[/b] 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]
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What is PRD?(Physical Region Descriptor)
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