MC68LC040RC25A Datasheet, PDF (101/442 Pages) Freescale Semiconductor, Inc – M68040 Users Manual

Freescale Semiconductor, Inc.
Table 4-4. Data-Cache Line State Transitions
Current State
Cache Operation
Invalid Cases
Valid Cases
Dirty Cases
CPU Read Miss
I1 Read line from
memory; supply data
to CPU and update
cache; go to valid
state.
V1 Read line from
D1 Buffer dirty cache line;
memory; supply data
read new line from
to CPU and update
memory; supply data
cache (replacing old
to CPU and update
line); remain in current
cache; write buffered
state.
dirty data to memory;
go to valid state.
CPU Read Hit
I2 Not Possible
V2 Supply data to CPU; D2 Supply data to CPU;
remain in current state.
remain in current state.
CPU Write Miss
(Copyback)
I3 Read line from
V3 Read line from
memory into cache;
memory into cache
write data to cache;
(replacing old line);
set Dn bits of modified
write data to cache
long words; go to dirty
and set Dn bits; go to
state.
dirty state.
D3 Buffer dirty cache line;
read new line from
memory; write data to
cache and set Dn bits;
write buffered dirty
data to memory;
remain in current state.
CPU Write Miss
(Write-through)
I4 Write data to memory; V4 Write data to memory; D4 Write data to memory;
remain in current state.
remain in current state.
remain in current state
(see note).
CPU Write Hit
(Copyback)
I5 Not Possible
V5 Write data into cache;
set Dn bits of modified
long words; go to dirty
state.
D5 Write data in cache;
set Dn bits of modified
long words; remain in
current state.
CPU Write Hit
(Write-through)
I6 Not Possible
V6 Write data to cache; D6 Write data into cache
write data to memory;
(no change to Dn bits);
remain in current state.
write data to memory;
remain in current state
(see note).
Cache Invalidate
(CINV)
I7 No action; remain in
current state.
V7 No action; go to invalid D7 No action (dirty data
state.
lost); go to invalid
state.
Cache Push
(CPUSH)
I8 No action; remain in
current state.
V8 No action; go to invalid D8 Write dirty data to
state.
memory; go to invalid
state.
Alternate Master Read Hit
(Snoop Control = 01
— Leave Dirty)
I9 Not Possible
V9 No action; remain in
current state.
D9 Inhibit memory and
source data; remain in
current state.
NOTE: Dirty state transitions D4 and D6 are the result of a system programming error and should be avoided even
though they are technically valid.
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