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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
August 2006
Developer’s Manual
Order Number: 306262-004US
189
Intel XScale
®
Processor—Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
3.9.4.10
Miscellaneous Instruction Timing
3.9.4.11
Thumb Instructions
In general, the timing of Thumb instructions are the same as their equivalent Intel
®
StrongARM
*
instructions, except for the cases listed below.
• If the equivalent Intel
®
StrongARM
*
instruction maps to one in
, the “Minimum Issue Latency with Branch Misprediction” goes from 5 to 6
cycles. This is due to the branch latency penalty. (See
• If the equivalent Intel
®
StrongARM
*
instruction maps to one in
, the “Minimum Issue Latency when the Branch is Taken” increases by 1
cycle. This is due to the branch latency penalty. (See
• A Thumb BL instruction when H = 0 will have the same timing as an Intel
®
StrongARM
*
data processing instruction.
The mapping of Thumb instructions to Intel
®
StrongARM
*
instructions can be found in
the ARM* Architecture Reference Manual.
3.10
Optimization Guide
3.10.1
Introduction
This document contains optimization techniques for achieving the highest performance
from the IXP45X/IXP46X network processors’ architecture. It is written for developers
who are optimizing compilers or performance analysis tools for the devices based on
these processors. It can also be used by application developers to obtain the best
performance from their assembly language code. The optimizations presented in this
section are based on the IXP45X/IXP46X network processors, and hence can be applied
to all products that are based on it.
The IXP45X/IXP46X network processors’ architecture includes a super-pipelined RISC
architecture with an enhanced memory pipeline. The instruction set for the IXP45X/
IXP46X network processors is based on the Intel
®
StrongARM
*
V5TE architecture;
however, the IXP45X/IXP46X network processors include new instructions. Code
generated for the SA110, SA1100 and SA1110 will execute on the IXP45X/IXP46X
network processors, however to obtain the maximum performance of your application
code, it should be optimized for the IXP45X/IXP46X network processors using the
techniques presented in this document.
Table 94.
Exception-Generating Instruction Timings
Mnemonic
Minimum latency to first instruction of exception handler
SWI
6
BKPT
6
UNDEFINED
6
Table 95.
Count Leading Zeros Instruction Timings
Mnemonic
Minimum Issue Latency
Minimum Result Latency
CLZ
1
1