AMD-K6-IIIE+550ACR AMD (ADVANCED MICRO DEVICES), AMD-K6-IIIE+550ACR Datasheet - Page 240

• Manufacturer Part Number: AMD-K6-IIIE+550ACR
• Manufacturer: AMD (ADVANCED MICRO DEVICES)

Specifications of AMD-K6-IIIE+550ACR

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AMD-K6™-IIIE+ Embedded Processor Data Sheet
Write Allocate Logic
Mechanisms and
Conditions
Figure 85. Write Allocate Logic Mechanisms and Conditions
218
1) CD Bit of CR0
2) PCD Signal
3) CI Bit of TR12
4) UC or WC
5) Write to Cacheable Page (CCR)
6) Write to a Sector
7) Less Than Limit (WAELIM)
8) Between 640 Kbytes and 1 Mbyte
9) Between 15–16 Mbytes
10) Write Allocate Enable 15–16 Mbyte (WAE15M)
Sector” mechanisms). The WAE15M bit is ignored if the value
in the WAELIM field is set to less than 16 Mbytes.
By definition a write allocate is 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 one
of the other write allocate mechanisms—“Write to a Cacheable
Page” and “Write to a Sector.” It is not considered 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.
If a memory region is defined as w rite combinable or
uncacheable by a MTRR, write allocates are not performed in
that region.
Figure 85 shows the logic flow for all the mechanisms involved
with write allocate for memory bus cycles. The left side of the
diagram (the text) describes the conditions that need to be true
in order for the value of that line to be a 1. Items 1 to 4 of the
diagram are related to general cache operation and items 5 to
10 are related to the write allocate mechanisms.
Fo r m o re i n f o r m a t i o n a b o u t w r i t e a l l o c a t e , s e e t h e
Implementation of Write Allocate in the K86™ Processors
Application Note, order# 21326.
Preliminary Information
Cache Organization
23543A/0—September 2000
Chapter 9
Perform
Write Allocate