11 CACHE CONTROLLER (CCU)
11-2
Seiko Epson Corporation
S1C33L26 TECHNICAL MANUAL
Cache Configuration
11.2
The CCU uses addresses 0x1f800 to 0x1fbff (1K bytes) and 0x1fc00 to 0x1ffff (1K bytes) in Area 0 for the instruc-
tion cache and the data cache, respectively. The instruction cache and the data cache can be separately enabled in
software. When using the CCU, take care not to allow data to be accidentally written to the cache from an applica-
tion. The cache memory spaces only store data sections; the TAG sections are stored in the memory within the CCU
module.
0x0001 ffff
0x0001 fc00
0x0001 fbff
0x0001 f800
0x0000 2fff
0x0000 0000
General-purpose RAM
(12KB)
Cache
controller
C33 PE Core
Data cache (1KB)
Instruction cache (1KB)
Area 0
SRAMC,
SDRAMC
External
memory
2.1
Figure 11.
Cache Memory
The CCU adopts the 4-Way set associative method.
One frame is composed of cache data containing four lines (4
×
4 words), and one Way consists of four frames.
Four frames located at the corresponding area in each Way are managed under one LRU entry.
Data to a cache from the external memory are loaded in units of a line (four words).
Figure 11.2.2 shows the cache configuration.
Frame 0
Frame 1
Frame 2
Frame 3
TAG
DATA
Way 0
Way 1
Way 2
Way 3
Line 3
Line 2
Line 1
Line 0
Way 0
Way 1
Way 2
Way 3
2.2 Cache Configuration
Figure 11.
TAG and Data Sections
Each frame is divided into the TAG and Data sections as shown in Figure 11.2.3. The TAG section stores 18-bit
addresses for comparison. The Data section consists of four words (16 bytes each) by four lines.
CA[25:8]
DATA
TAG
Line 3
Line 2
Line 1
Line 0
18 bits
Address for comparison
4 words
4 words
4 words
4 words
W3
W2
W1
W0
32 bits
32 bits
32 bits
32 bits
128 bits
2.3 Frame Configuration
Figure 11.
LRU Section
Configured with 4-Ways, the CCU has four frames of data assigned the same entry number. If nothing is hit, it
is needed to select one of the four Ways to replace with, in which case, the LRU section stores the Way number.