System Control
ARM DDI 0500D
Copyright © 2013-2014 ARM. All rights reserved.
4-77
ID021414
Non-Confidential
Table 4-77
shows the SCR_EL3 bit assignments.
Table 4-77 SCR_EL3 bit assignments
Bits
Name
Function
[31:14]
-
Reserved,
RES
0.
[13]
TWE
Traps
WFE
instructions. The possible values are:
0
WFE
instructions are not trapped. This is the reset value.
1
WFE
instructions executed in AArch32 or AArch64 from EL2, EL1 or EL0 are trapped to EL3 if
the instruction would otherwise cause suspension of execution, that is if:
•
The event register is not set.
•
There is not a pending WFE wakeup event.
•
The instruction is not trapped at EL2 or EL1.
See the
ARM
®
Architecture Reference Manual ARMv8, for ARMv8-A architecture profile
for more information.
[12]
TWI
Traps
WFI
instructions. The possible values are:
0
WFI
instructions are not trapped. This is the reset value.
1
WFI
instructions executed in AArch32 or AArch64 from EL2, EL1 or EL0 are trapped to EL3 if
the instruction would otherwise cause suspension of execution, that is if there is not a pending
WFI wakeup event and the instruction is not trapped at EL2 or EL1.
See the
ARM
®
Architecture Reference Manual ARMv8, for ARMv8-A architecture profile
for more information.
[11]
ST
Enable Secure EL1 access to CNTPS_TVAL_EL1, CNTS_CTL_EL1, and CNTPS_CVAL_EL1 registers. The
possible values are:
0
Registers accessible only in EL3. This is the reset value.
1
Registers accessible in EL3 and EL1 when SCR_EL3.NS is 0.