AMD-K6-2E/400AFR AMD [Advanced Micro Devices], AMD-K6-2E/400AFR Datasheet - Page 217

• Manufacturer Part Number: AMD-K6-2E/400AFR
• Manufacturer: AMD [Advanced Micro Devices]

22529B/0—January 2000
8.10
Inquire Cycles
Internal Snooping
Chapter 8
Cache Coherency
Different methods exist to maintain coherency between the
system memory and cache memories. Inquire cycles, internal
snoops, FLUSH#, WBINVD, INVD, and line replacements all
prevent inconsistencies between memories.
Inquire cycles are bus cycles initiated by system logic. These
inquiries ensure coherency between the caches and main
memory. In systems with multiple caching masters, system logic
maintains cache coherency by driving inquire cycles to the
processor. System logic initiates inquire cycles by asserting
AHOLD, BOFF#, or HOLD to obtain control of the address bus
and then driving EADS#, INV (optional), and an inquire
address (A[31:5]).
This type of bus cycle causes the processor to compare the tags
for both its instruction and data caches with the inquire
address.
Table 35 on page 202 shows the effects of inquire cycles—
performed with INV equal to 0 (non-validating) and INV equal
to 1 (invalidating) snoops and invalidations.
Internal snooping is initiated by the processor (rather than
system logic) during certain cache accesses. It is used to
maintain coherency between the L1 instruction and data
caches.
The processor automatically snoops its instruction cache during
read or write misses to its data cache, and it snoops its data
If there is a hit to a shared or exclusive line in the data cache
or a valid line in the instruction cache, the processor asserts
HIT#.
If the compare hits a modified line in the data cache, the
processor asserts HIT# and HITM#. If HITM# is asserted, the
processor writes the modified line back to memory.
If INV was sampled asserted with EADS#, a hit invalidates
the line.
If INV was sampled negated with EADS#, a hit leaves the
line in the Shared state or transitions it from the Exclusive
or Modified to Shared state.
Cache Organization
AMD-K6™-2E Processor Data Sheet
199