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| 型號(hào)： | 21326 |
| 英文描述： | Implementation of Write Allocate Application Note |
| 中文描述： | 在寫分配應(yīng)用執(zhí)行情況的說明 |
| 文件頁數(shù)： | 13/22頁 |
| 文件大小： | 241K |
| 代理商： | 21326 |
Programming Details
5
21326F/0—February 1999
Implementation of Write Allocate in the K86 Processors
Once the BIOS determines the amount of RAM installed in the
system, this number should also be used to program the
WAELIM field. For example, a system with 32 Mbytes of RAM
would program the WAELIM field with the value 000_1000b.
This value (8), when multiplied by 4 Mbytes, yields 32 Mbytes
as the write allocate limit.
Write Allocate Enable 15-to-16-Mbyte.
The WAE15M bit is used to
enable write allocations for memory write cycles that address
the 1 Mbyte of memory between 15 Mbytes and 16 Mbytes. This
bit must be set to 1 to allow write allocates in this memory area.
This sub-mechanism of the WAELIM provides a memory hole to
prevent write allocates. This memory hole is provided to
account for a small number of uncommon memory-mapped I/O
adapters that use this particular memory address space. If the
system contains one of these peripherals, the bit should be set
to 0 (even if the WAE15M bit is set to 0, write allocates can still
occur between 15 Mbytes and 16 Mbytes due to the “Write to a
Cacheable Page” and “Write to a Sector” mechanisms). The
WAE15M bit is ignored if the value in the WAELIM field is set
to less than 16 Mbytes.
By definition, write allocations in the AMD-K6 are not
performed in the memory area between 640 Kbytes and 1
Mbyte unless the processor determines a pending write cycle is
cacheable by means of “Write to a Cacheable Page” or “Write
to a Sector.” It is not safe to perform write allocations between
640 Kbytes and 1 Mbyte (000A_0000h to 000F_FFFFh) because
it is considered a noncacheable region of memory.
To complete programming write allocate on the AMD-K6
processor, go to “Step 3: AMD-K6
Processor (All Models)
” on
page 8.
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