Motorola MC68030 User Manual page 147

In this case, the data in the cache no longer matches that in physical memory
and is stale. Since the write-allocation mode updates the cache during write
cycles, the data in the cache remains consistent with physical memory. Note
that when ClOUT is asserted, the data cache is completely ignored, even on
write cycles operating in the write-allocation mode. Also note that since the
CIIN signal is ignored on write cycles, cache entries may be created for
noncachable data (when CIIN is asserted on a write) when operating in the
write-allocation mode. Figure 6-4 shows the manner in which each mode
operates in five different situations.
TAG'
I
LOGICAL AOORESS
=
FC2·FCO. A31·AS. A7·A4, A3·A2
LINE
SELECT
($5)
USER OATA. $000010
TAG
EXAMPLE 1:
USER WORO WRITE OF b2'·b3' TO $00001052
(CACHE HIT. ALWAYS UPDATE CACHE AND MEMDRY)
(
EXAMPLE 2:
USER LONG WORD WRITE OF bS'·b9' TO $00001056
(TAG MATCH. LONG WDRD DATA. MISALIGNED.
b6·b7 RESULT IN A CACHE MISS.
bS·b9 RESULT IN A CACHE HIT)
EXAMPLE 3:
ENTRY SELECT
NO'WRITE:ALLOCATE
A) START EXTERNAL CYCLE
B)
b2·b3"- b2'·b3'
A) START EXTERNAL CYCLE
B) bS·b9"- bS'·b9'
USER LDNG WORD WRITE OF b4'·b7' TO $00001054 A) START EXTERNAL CYCLE
(TAG MATCH. CACHE MISS. LONG WDRD DATA.
LONG WORD ALIGNED)
EXAMPLE 4:
USER LONG WORD WRITE OF b4'·b7' TO $00002054 A) START EXTERNAL CYCLE
(NO TAG MATCH. LONG WORD DATA. LONG WDRD ALIGNED)
EXAMPLE 5:
USER LONG WORD WRITE OF bS'·b9' TO $00002056
(ND TAG MATCH. LONG WORD DATA. MISALIGNED)
A) START EXTERNAL CYCLE
WRITE,ALLOCATE
A) START EXTERNAL CYCLE
B) b2·b3"- b2'·b3'
A) START EXTERNAL CYCLE
B)
bS·b9"- bS'·b9'
A) START EXTERNAL CYClE
B)
b4·b7..-b4'·b7'
C) Vl"-l
A) START EXTERNAL CYCLE
B) TAG..-TAG'
C) b4·b7"- b4'·b7'
D) VO"- 0
Vl"-l
V2"-0
V3"-0
A) START EXTERNAL CYClE
B) V2"- 0
Figure 6-4. No-Write-Allocation and Write-Allocation Mode Examples
MOTOROLA
MC68030 USER'S MANUAL
6-9
III