AMD-K6-2ESLASH233AMZ datasheet(212/332 Pages) AMD

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194

Cache Organization

Chapter 8

AMD-K6™-2E Processor Data Sheet

22529B/0—January 2000

Preliminary Information

Write Handling Control Register (WHCR) . Th e

W H C R

re gi s t er

contains two fields —the Write Allo cate Enab le Limit

(WAELIM) field, and the Write Allocate Enable 15-to-16-Mbyte

(WAE15M) bit (see Figure 76).

Figure 76. Write Handling Control Register (WHCR)

Write Allocate Enable Limit Field. The WAELIM field is 10 bits wide.

This field, multiplied by 4 Mbytes, defines an upper memory

limit. Any pending write cycle that addresses memory below

this limit causes the processor to perform a write allocate

(assuming the address is not within a range where write

allocates are disallowed). Write allocate is disabled for memory

accesses at and above this limit unless the processor determines

a pending write cycle is cacheable by means of one of the other

write allocate mechanisms —“Write to a Cacheable Page” and

“Write to a Sector.” The maximum value of this limit is ((210–1)

· 4 Mbytes) = 4092 Mbytes. When all the bits in this field are 0,

all memory is above this limit and the write allocate mechanism

is disabled (even if all bits in the WAELIM field are 0, write

allocates can still occur due to the “Write to a Cacheable Page”

and “Write to a Sector” mechanisms).

Write Allocate Enable 15-to-16-Mbyte Bit. The Write Allocate Enable

15 -t o-16-Mbyte (WAE 15M ) bi t is us ed to enab l e wri t e

allocations for the 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 allocate in this memory area. This

bit 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 written to 0 (even if the WAE15M bit is 0,

WAELIM

Note: Hardware RESET initializes this MSR to all zeros.

Symbol

Description

Bits

WAELIM

Write Allocate Enable Limit

31-22

WAE15M

Write Allocate Enable 15-to-16-Mbyte 16

Reserved

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