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Intel
®
IXP42X product line and IXC1100 control plane processors—Intel XScale
®
Processor
Intel
®
IXP42X Product Line of Network Processors and IXC1100 Control Plane Processor
DM September 2006
152 Order Number: 252480-006US
This instruction executes in any processor mode.
3.8.3.2 New Page Attributes
The Intel XScale processor extends the page attributes defined by the C and B bits in
the page descriptors with an additional X bit. This bit allows four more attributes to be
encoded when X=1. These new encodings include allocating data for the mini-data
cache and write-allocate caching. A full description of the encodings can be found in
“Memory Attributes” on page 45.
The Intel XScale processor retains ARM definitions of the C and B encoding when X = 0,
which is different than the ARM products. The memory attribute for the mini-data cache
has been moved and replaced with the write-through caching attribute.
When write-allocate is enabled, a store operation that misses the data cache
(cacheable data only) will generate a line fill. If disabled, a line fill only occurs when a
load operation misses the data cache (cacheable data only).
Write-through caching causes all store operations to be written to memory, whether
they are cacheable or not cacheable. This feature is useful for maintaining data cache
coherency.
Bit 1 in the Control Register (coprocessor 15, register 1, opcode=1) is used reserved
for the P bit memory attribute for memory accesses made during page table walks. The
P bit is not implemented on IXP42X product line and IXC1100 control plane processors.
These attributes are programmed in the translation table descriptors, which are
highlighted in:
• Table 69, “First-Level Descriptors” on page 153
• Table 70, “Second-Level Descriptors for Coarse Page Table” on page 153
• Table 71, “Second-Level Descriptors for Fine Page Table” on page 153
Two second-level descriptor formats have been defined for the IXP42X product line and
IXC1100 control plane processors, one is used for the coarse page table and the other
is used for the fine page table.