System Control
ARM DDI 0500D
Copyright © 2013-2014 ARM. All rights reserved.
4-201
ID021414
Non-Confidential
To access the SCR:
MRC p15,0,<Rt>,c1,c1,0 ; Read SCR into Rt
MCR p15,0,<Rt>,c1,c1,0 ; Write Rt to SCR
4.5.31
Secure Debug Enable Register
The SDER characteristics are:
Purpose
Controls invasive and non-invasive debug in the Secure EL0 state.
[9]
SIF
Secure Instruction Fetch. When the processor is in Secure state, this bit disables instruction fetches from
Non-secure memory. The possible values are:
0
Secure state instruction fetches from Non-secure memory permitted. This is the reset value.
1
Secure state instruction fetches from Non-secure memory not permitted.
[8]
HCE
Hyp Call enable. This bit enables use of the HVC instruction from Non-secure EL1 modes. The possible values
are:
0
The
HVC
instruction is
UNDEFINED
in any mode. This is the reset value.
1
The
HVC
instruction enabled in Non-secure EL1, and performs a Hyp Call.
[7]
SCD
Secure Monitor Call disable. Makes the SMC instruction
UNDEFINED
in Non-secure state. The possible values are:
0
SMC
executes normally in Non-secure state, performing a Secure Monitor Call. This is the reset
value.
1
The
SMC
instruction is
UNDEFINED
in Non-secure state.
A trap of the SMC instruction to Hyp mode takes priority over the value of this bit.
[6]
nET
Not Early Termination. This bit disables early termination.
This bit is not implemented,
RES
0.
[5]
AW
A bit writable. This bit controls whether CPSR.A can be modified in Non-secure state.
•
CPSR.A can be modified only in Secure state. This is the reset value.
•
CPSR.A can be modified in any security state.
[4]
FW
F bit writable. This bit controls whether CPSR.F can be modified in Non-secure state:
•
CPSR.F can be modified only in Secure state. This is the reset value.
•
CPSR.F can be modified in any security state.
[3]
EA
External Abort handler. This bit controls which mode takes external aborts. The possible values are:
0
External aborts taken in abort mode. This is the reset value.
1
External aborts taken in Monitor mode.
[2]
FIQ
FIQ handler. This bit controls which mode takes FIQ exceptions. The possible values are:
0
FIQs taken in FIQ mode. This is the reset value.
1
FIQs taken in Monitor mode.
[1]
IRQ
IRQ handler. This bit controls which mode takes IRQ exceptions. The possible values are:
0
IRQs taken in IRQ mode. This is the reset value.
1
IRQs taken in Monitor mode.
[0]
NS
Non-secure bit. Except when the processor is in Monitor mode, this bit determines the security state of the
processor. The possible values are:
0
Processor is in secure state. This is the reset value.
1
Processor is in non-secure state.
Table 4-196 SCR bit assignments (continued)
Bits
Name
Function