mpc823rg Freescale Semiconductor, Inc, mpc823rg Datasheet - Page 195

• Manufacturer Part Number: mpc823rg
• Description: Mpc823 Powerquicc Integrated Communications Processor For Portable Systems
• Manufacturer: Freescale Semiconductor, Inc

9.2.3 Instruction Cache Data Port Register
The instruction cache data port register (IC_DAT) contains data that is received from the
instruction cache.
DAT—Data
This field represents the data received when reading information from the instruction cache.
The format may vary depending on the selected cache.
9.3 INSTRUCTION CACHE OPERATION
On an instruction fetch, bits 22-27 of the instruction’s address point into the cache to retrieve
the tags and data of one set. The tags from both ways are then compared against bits 0-21
of the instruction’s address. If a match is found and the matched entry is valid, then it is a
cache hit. If none of the tags match or the matched tag is not valid, it is a cache miss. The
instruction cache includes one burst buffer that holds the last line received from the bus and
one line buffer that holds the last line retrieved from the cache array. If the requested data
is found in one of these buffers, it can also be considered a cache hit. Refer to Figure 9-2
for more information. To minimize power consumption, the instruction cache attempts to
make use of data stored in one of its internal buffers. Using a special indication from the
core, it is possible to make sure that the requested data is in one of the buffers early enough
that the cache array is not activated.
9.3.1 Instruction Cache Hit
When a cache hit occurs, bits 28-29 of the instruction address are used to select one word
from the cache line whose tag matches the instruction pointer. The instruction is then
immediately transferred to the instruction unit of the core.
IC_DAT
NOTE: — = Undefined.
RESET
RESET
FIELD
FIELD
SPR
SPR
R/W
R/W
BIT
BIT
16
0
17
1
18
2
Freescale Semiconductor, Inc.
For More Information On This Product,
19
3
20
MPC823 REFERENCE MANUAL
4
Go to: www.freescale.com
21
5
22
6
23
7
DAT
DAT
R/W
R/W
562
562
—
—
24
8
25
9
10
26
11
27
12
28
Instruction Cache
13
29
14
30
15
31
9-7