![Freescale Semiconductor MCF54455 Reference Manual Download Page 167](http://html1.mh-extra.com/html/freescale-semiconductor/mcf54455/mcf54455_reference-manual_2330541167.webp)
Cache
6-22
Freescale Semiconductor
6.4.7.2
Data Cache-State Transitions
Using the V and M bits, the data cache supports a line-based protocol allowing individual cache lines to
be invalid, valid, or modified. To maintain coherency with memory, the data cache supports write-through
and copyback modes, specified by the corresponding ACR[CM], or CACR[DDCM] if no ACR matches.
Read or write misses to copyback regions cause the cache controller to read a cache line from memory into
the cache. If available, tag and data from memory update an invalid line in the selected set. The line state
then changes from invalid to valid by setting the V bit for the line. If all lines in the row are already valid
or modified, the pseudo-round-robin replacement algorithm selects one of the four lines and replaces the
tag and data. Before replacement, modified lines are buffered temporarily and later copied back to memory
after the new line has been read from memory.
shows the three possible data-cache line states and possible processor-initiated transitions for
memory configured as copyback. Transitions are labeled with a capital letter indicating the previous state
and a number indicating the specific case listed in
.
Figure 6-11. Data Cache Line State Diagram—Copyback Mode
shows the two possible states for a cache line in write-through mode.
Figure 6-12. Data-Cache Line State Diagram—Write-Through Mode
describes data-cache line transitions and what accesses cause them.
Invalid
CD1—CPU
CI3—CPU
Valid
V = 1
Modified
read miss
write miss
CI5—DCINVA
CI6—CPUSHL and
DDPI
CI7—CPUSHL and
CV1—CPU read miss
CV2—CPU read hit
CV7—CPUSHL and
CD2—CPU read hit
CD3—CPU write miss
CD4—CPU write hit
CD5—DCINVA
CD6—CPUSHL and DDPI
CV3—CPU write miss
CV4—CPU write hit
CI1—CPU read miss
CV5—DCINVA
CV6—CPUSHL and
V = 0
M = 0
V = 1
M = 1
CD7—CPUSHL
and DDPI
WI1—CPU read miss
Invalid
Valid
WI3—CPU write miss
WI5—DCINVA
WI6—CPUSHL and DDPI
WI7—CPUSHL and DDPI
WV1—CPU read miss
WV2—CPU read hit
WV3—CPU write miss
WV4—CPU write hit
WV7—CPUSHL and
WV5—DCINVA
WV6—CPUSHL and
V = 0
V = 1
Summary of Contents for MCF54455
Page 33: ...xxviii Freescale Semiconductor ...
Page 67: ...Freescale Semiconductor 1 ...
Page 125: ...Freescale Semiconductor 1 ...
Page 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
Page 173: ...Cache 6 28 Freescale Semiconductor ...
Page 179: ...Static RAM SRAM 7 6 Freescale Semiconductor ...
Page 207: ...Power Management 9 16 Freescale Semiconductor ...
Page 323: ...Reset Controller Module 13 8 Freescale Semiconductor ...
Page 389: ...Pin Multiplexing and Control 16 44 Freescale Semiconductor ...
Page 575: ...PCI Bus Controller 22 58 Freescale Semiconductor ...
Page 600: ...Advanced Technology Attachment ATA Freescale Semiconductor 23 25 ...
Page 601: ...Freescale Semiconductor 1 ...
Page 842: ...I2 C Interface Freescale Semiconductor 33 16 ...
Page 843: ...Freescale Semiconductor 1 ...
Page 921: ...Revision History A 6 Freescale Semiconductor ...