MOTOROLA
M68040 USER’S MANUAL
4- 17
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
memory; supply data
to CPU and update
cache (replacing old
line); remain in current
state.
D1
Buffer dirty cache line;
read new line from
memory; supply data
to CPU and update
cache; write buffered
dirty data to memory;
go to valid state.
CPU Read Hit
I2
Not Possible
V2
Supply data to CPU;
remain in current state.
D2
Supply data to CPU;
remain in current state.
CPU Write Miss
(Copyback)
I3
Read line from
memory into cache;
write data to cache;
set Dn bits of modified
long words; go to dirty
state.
V3
Read line from
memory into cache
(replacing old line);
write data to cache
and set Dn bits; go to
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;
remain in current state.
V4
Write data to memory;
remain in current state.
D4
Write data to memory;
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;
write data to memory;
remain in current state.
D6
Write data into cache
(no change to Dn bits);
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
state.
D7
No action (dirty data
lost); go to invalid
state.
Cache Push
(CPUSH)
I8
No action; remain in
current state.
V8
No action; go to invalid
state.
D8
Write dirty data to
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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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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