AN2203 Freescale Semiconductor / Motorola, AN2203 Datasheet - Page 35

• Manufacturer Part Number: AN2203
• Description: MPC7450 RISC Microprocessor Family Software Optimization Guide
• Manufacturer: Freescale Semiconductor / Motorola

3.7
The LSU has two reservation stations. Instruction execution is allowed only from the bottom reservation
station (reservation station 0).
The 32-Kbyte, 8-way data cache has a cache line size of 32 bytes. The replacement algorithm is
pseudo-LRU (PLRU). The LSU on the MPC7450 is different from prior designs in many ways. The most
critical is that load latencies are now one (or two for load-float) cycle longer than in previous
microprocessors.
3.7.1
The following code sequence shows the various normal load latencies:
xxxxxx00
xxxxxx04
xxxxxx08
xxxxxx0C
xxxxxx10
xxxxxx14
xxxxxx18
As Table 3-20 shows, the load-floating-point latency is four cycles and the load-integer and load-vector
latency are each three cycles. Although the load has a 4-cycle latency, it also completes on that fourth cycle.
The update has an effective latency of one. The lwzu forwards its update target R11 from E0 in cycle 3 to
the subf instruction, such that it executes in cycle 4.
MOTOROLA
Instr.
No.
0
1
2
3
4
5
6
Load/Store Unit (LSU)
lfdu
fadd
lwzu
add
subf
lvewx
vaddsws
Instruction
Load Hit Pipeline
vaddfp
vsubfp
vlogefp
vcmpbfp.
vmaddfp
Instruction
MPC7450 RISC Microprocessor Family Software Optimization Guide
lfdu f3,0x8(r10)
fadd f1,f3,f4
lwzu r3,0x4(r11)
add r1,r3,r4
subf r5,r11,r6
lvewx v3,r12,r13
vaddsws v1,v3,v4
F2
F2
F2
—
—
D
D
0
Freescale Semiconductor, Inc.
F2
—
—
D
D
0
For More Information On This Product,
—
—
D
D
D
1
I
I
Table 3-20. Load Hit Pipeline Example
—
—
D
D
1
I
Table 3-19. Vector Unit Example
E0
—
D
D
2
I
I
I
Go to: www.freescale.com
E0
—
—
D
2
I
E1
E0
—
—
—
3
I
I
E1
E0
—
—
3
E2
E1
E0
I
—
—
—
E
4
E3/C
E2
E1
E0
—
4
E2
E1
I
—
—
—
—
5
E3
E2
E1
E0
5
E0
E2
I
—
—
—
6
E
E2
E1
E3
E0
E1
C
6
—
—
—
—
E
7
E3
E2
E1
E2
—
—
—
—
—
7
8
F
E3
—
—
—
—
—
E3
E2
—
9
C
8
Load/Store Unit (LSU)
10
E4
—
—
—
—
—
E3
C
C
9
11
—
—
—
—
—
F
10
C
12
—
—
—
C
C
C
13
C
C
C
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