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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
August 2006
Developer’s Manual
Order Number: 306262-004US
191
Intel XScale
®
Processor—Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
3.10.2.1.2
Processor Pipeline Organization
The IXP45X/IXP46X network processors’ single-issue super-pipeline consists of a main
execution pipeline, MAC pipeline, and a memory access pipeline. These are shown in
, with the main execution pipeline shaded.
gives a brief description of each pipe-stage.
3.10.2.1.3
Out-of-Order Completion
Sequential consistency of instruction execution relates to two aspects: first, to the
order in which the instructions are completed; and second, to the order in which
memory is accessed due to load and store instructions. The IXP45X/IXP46X network
processors preserve a weak processor consistency because instructions may complete
out of order, provided that no data dependencies exist.
Figure 27.
RISC Super-Pipeline
B4354-01
F1
F2
ID
RF
D1
D2
DWB
X1
X2
XWB
Mx
M1
M2
Main Execution Pipeline
Mac Pipeline
Memory Pipeline
Table 96.
Pipelines and Pipe Stages
Pipe / Pipe State
Description
Covered In
Main Execution Pipeline
Handles data processing instructions
IF1/IF2
Instruction Fetch
“
ID
Instruction Decode
“
RF
Register File / Operand Shifter
“
X1
ALU Execute
“
X2
State Execute
“
XWB
Write-back
“
Memory Pipeline
Handles load/store instructions
D1/D2
Data Cache Access
“
DWB
Data cache writeback
“
MAC Pipeline
Handles all multiply instructions
M1-M5 Multiplier
stages
“
MWB (not shown)
MAC write-back - may occur during M2-M5
“