Access Flag Enable. This bit enables use of the AP[0] bit in the translation descriptors as the
Access flag. It also restricts access permissions in the translation descriptors to the simplified
model:
0
In the translation table descriptors, AP[0] is an access permissions bit. The full range
of access permissions is supported. No Access flag is implemented. This is the reset
value.
1
In the translation table descriptors, AP[0] is the Access flag. Only the simplified
model for access permissions is supported.
TRE, [28]
TEX remap enable. This bit enables remapping of the TEX[2:1] bits for use as two translation
table bits that can be managed by the operating system. Enabling this remapping also changes
the scheme used to describe the memory region attributes in the VMSA:
0
TEX remap disabled. TEX[2:0] are used, with the C and B bits, to describe the
memory region attributes. This is the reset value.
1
TEX remap enabled. TEX[2:1] are reassigned for use as bits managed by the operating
system. The TEX[0], C and B bits are used to describe the memory region attributes,
with the MMU remap registers.
[27:26]
Reserved,
RES0
.
EE, [25]
Exception Endianness bit. The value of this bit defines the value of the CPSR.E bit on entry to
an exception vector, including reset. This value also indicates the endianness of the translation
table data for translation table lookups:
0
Little endian.
1
Big endian.
The input
CFGEND
defines the reset value of the EE bit.
[24]
Reserved,
RES0
.
[23:22]
Reserved,
RES1
.
[21]
Reserved,
RES0
.
UWXN, [20]
Unprivileged write permission implies EL1
Execute Never
(XN). This bit can be used to require
all memory regions with unprivileged write permissions to be treated as XN for accesses from
software executing at EL1.
0
Regions with unprivileged write permission are not forced to be XN, this is the reset
value.
1
Regions with unprivileged write permission are forced to be XN for accesses from
software executing at EL1.
WXN, [19]
Write permission implies
Execute Never
(XN). This bit can be used to require all memory
regions with write permissions to be treated as XN.
B1 AArch32 system registers
B1.105 System Control Register
100236_0100_00_en
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B1-332
Non-Confidential
Summary of Contents for Cortex-A35
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