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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
August 2006
Developer’s Manual
Order Number: 306262-004US
169
Intel XScale
®
Processor—Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
• PLD is interpreted as a read operation by the MMU and is ignored by the data
breakpoint unit, i.e., PLD will never generate data breakpoint events.
• PLD to a non-cacheable page performs no action. Also, if the targeted cache line is
already resident, this instruction has no affect.
• Both LDRD and STRD instructions will generate an alignment exception when the
address bits [2:0] = 0b100.
The transfers of two Intel StrongARM register values to a coprocessor (MCRR) and the
transfer of values from a coprocessor to two Intel StrongARM registers (MRRC) are only
supported on the IXP45X/IXP46X network processors when directed to coprocessor 0
and are used to access the internal accumulator. See
for more information. Access to coprocessors 15 and 14 generate
an undefined instruction exception.
3.8.2.5
Base Register Update
If a data abort is signalled on a memory instruction that specifies write-back, the
contents of the base register will not be updated. This holds for all load and store
instructions. This behavior matches that of the first generation Intel StrongARM
processor and is referred to in the Intel StrongARM V5TE architecture as the Base
Restored Abort Model.
3.8.3
Extensions to Intel
®
StrongARM
*
Architecture
The Intel XScale processor adds a few extensions to the Intel StrongARM Version 5TE
architecture to meet the needs of various markets and design requirements. The
following is a list of the extensions which are discussed in the next sections.
• A DSP coprocessor (CP0) has been added that contains a 40-bit accumulator and
eight new instructions.
• New page attributes were added to the page table descriptors. The C and B page
attribute encoding was extended by one more bit to allow for more encodings:
write allocate and mini-data cache.
• Additional functionality has been added to coprocessor 15. Coprocessor 14 was also
created.
• Enhancements were made to the Event Architecture, which include instruction
cache and data cache parity error exceptions, breakpoint events, and imprecise
external data aborts.
3.8.3.1
DSP Coprocessor 0 (CP0)
The Intel XScale processor adds a DSP coprocessor to the architecture for the purpose
of increasing the performance and the precision of audio processing algorithms. This
coprocessor contains a 40-bit accumulator and eight new instructions.
The 40-bit accumulator is referenced by several new instructions that were added to
the architecture; MIA, MIAPH and MIAxy are multiply/accumulate instructions that
reference the 40-bit accumulator instead of a register specified accumulator. MAR and
MRA provide the ability to read and write the 40-bit accumulator.
Access to CP0 is always allowed in all processor modes when bit 0 of the Coprocessor
Access Register is set. Any access to CP0 when this bit is clear will cause an undefined
exception. (See
“Register 15: Coprocessor Access Register” on page 107
for more
details). Note that only privileged software can set this bit in the Coprocessor Access
Register located in CP15.
The 40-bit accumulator will need to be saved on a context switch if multiple processes
are using it.