ARM Cortex-M4 - Msr

The Cortex-M4 Instruction Set
ARM DUI 0553A Copyright © 2010 ARM. All rights reserved. 3-164
ID121610 Non-Confidential
3.12.7 MSR
Move the contents of a general-purpose register into the specified special register.
Syntax
MSR{cond} spec_reg, Rn
where:
cond Is an optional condition code, see Conditional execution on page 3-18.
Rn Specifies the source register.
spec_reg Can be any of: APSR_nzcvq , APSR_g , APSR_nzcvqg , MSP , PSP , PRIMASK , BASEPRI ,
BASEPRI_MAX , FAULTMASK , or CONTROL .
Note
You can use APSR to refer to APSR_nzcvq .
Operation
The register access operation in
MSR depends on the privilege level. Unprivileged software can
only access the
APSR , see Table 2-4 on page 2-5. Privileged software can access all special
registers.
In unprivileged software writes to unallocated or execution state bits in the
PSR are ignored.
Note
When you write to BASEPRI_MAX , the instruction writes to BASEPRI only if either:
•
Rn is non-zero and the current BASEPRI value is 0
•
Rn is non-zero and less than the current BASEPRI value.
See MRS on page 3-163.
Restrictions
Rn must not be SP and must not be PC.
Condition flags
This instruction updates the flags explicitly based on the value in Rn.
Examples
MSR CONTROL, R1 ; Read R1 value and write it to the CONTROL register