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Write-Combining Definitions and Abbreviations
AMD Athlon™ Processor x86 Code Optimization
22007E/0—November 1999
Write-Combining Definitions and Abbreviations
This appendix uses the following definitions and abbreviations:
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UC—Uncacheable memory type
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WC—Write-combining memory type
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WT—Writethrough memory type
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WP—Write-protected memory type
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WB—Writeback memory type
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One Byte—8 bits
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One Word—16 bits
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Longword—32 bits (same as a x86 doubleword)
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Quadword—64 bits or 2 longwords
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Octaword—128 bits or 2 quadwords
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Cache Block—64 bytes or 4 octawords or 8 quadwords
What is Write Combining?
Write combining is the merging of multiple memory write
cycles that target locations within the address range of a write
b u f f e r. The A MD A t h lo n p ro c e ss or c o m b ine s multi p le
memory-write cycles to a 64-byte buffer whenever the memory
address is within a WC or WT memory type region. The
processor continues to combine writes to this buffer without
writing the data to the system, as long as certain rules apply
(see Table 9 on page 158 for more information).
Programming Details
The steps required for programming write combining on the
AMD Athlon processor are as follows:
1. Verify the presence of an AMD Athlon processor by using
the CPUID instruction to check for the instruction family
code and vendor identification of the processor. Standard
function 0 on AMD processors returns a vendor
identification string of “AuthenticAMD” in registers EBX,
EDX, and ECX. Standard function 1 returns the processor
Summary of Contents for Athlon Processor x86
Page 1: ...AMD Athlon Processor x86 Code Optimization Guide TM...
Page 12: ...xii List of Figures AMD Athlon Processor x86 Code Optimization 22007E 0 November 1999...
Page 16: ...xvi Revision History AMD Athlon Processor x86 Code Optimization 22007E 0 November 1999...
Page 202: ...186 Page Attribute Table PAT AMD Athlon Processor x86 Code Optimization 22007E 0 November 1999...
Page 252: ...236 VectorPath Instructions AMD Athlon Processor x86 Code Optimization 22007E 0 November 1999...
Page 256: ...240 Index AMD Athlon Processor x86 Code Optimization 22007E 0 November 1999...