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Intel
®
IXP42X Product Line of Network Processors and IXC1100 Control Plane Processor
September 2006 DM
Order Number: 252480-006US 153
Intel XScale
®
Processor—Intel
®
IXP42X product line and IXC1100 control plane processors
The TEX (Type Extension) field is present in several of the descriptor types. In the Intel
XScale processor, only the LSB of this field is defined; this is called the X bit. The
remaining bits are reserved for future use and should be programmed as zero (SBZ) on
the IXP42X product line and IXC1100 control plane processors.
A Small Page descriptor does not have a TEX field. For these descriptors, TEX is
implicitly zero; that is, they operate as if the X bit had a ‘0’ value.
The X bit, when set, modifies the meaning of the C and B bits. Description of page
attributes and their encoding can be found in “Memory Management Unit” on page 44.
3.8.3.3 Additions to CP15 Functionality
To accommodate the functionality in the Intel XScale processor, registers in CP15 and
CP14 have been added or augmented. See “Configuration” on page 73 for details.
At times it is necessary to be able to guarantee exactly when a CP15 update takes
effect. For example, when enabling memory address translation (turning on the MMU),
it is vital to know when the MMU is actually guaranteed to be in operation. To address
this need, a processor-specific code sequence is defined for the Intel XScale processor.
The sequence — called CPWAIT — is shown in Example 12 on page 86.
Table 69. First-Level Descriptors
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
SBZ 0 0
Coarse page table base address P Domain SBZ 0 1
Section base address SBZ TEX AP P Domain 0 C B 1 0
Fine page table base address SBZ P Domain SBZ 1 1
Table 70. Second-Level Descriptors for Coarse Page Table
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
SBZ 0 0
Large page base address TEX AP3 AP2 AP1 AP0 C B 0 1
Small page base address AP3 AP2 AP1 AP0 C B 1 0
Extended small page base address SBZ TEX AP C B 1 1
Table 71. Second-Level Descriptors for Fine Page Table
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
SBZ 0 0
Large page base address TEX AP3 AP2 AP1 AP0 C B 0 1
Small page base address AP3 AP2 AP1 AP0 C B 1 0
Tiny Page Base Address TEX AP C B 1 1