The STM32 Cortex-M4 instruction set PM0214
186/262 PM0214 Rev 9
3.11.6 MRS
Move the contents of a special register to a general-purpose register.
Syntax
MRS{cond} Rd, spec_reg
Where:
• ‘cond’ is an optional condition code, see Conditional execution on page 65.
• ‘Rd’ is the destination register.
• ‘spec_reg’ can be any of: APSR, IPSR, EPSR, IEPSR, IAPSR, EAPSR, PSR, MSP,
PSP, PRIMASK, BASEPRI, BASEPRI_MAX, FAULTMASK, or CONTROL.
Operation
Use MRS in combination with MSR as part of a read-modify-write sequence for updating a
PSR, for example to clear the Q flag. See MSR on page 187.
In process swap code, the programmers model state of the process being swapped out
must be saved, including relevant PSR contents. Similarly, the state of the process being
swapped in must also be restored. These operations use MRS in the state-saving
instruction sequence and MSR in the state-restoring instruction sequence.
BASEPRI_MAX is an alias of BASEPRI when used with the MRS instruction.
Restrictions
Rd must not be SP and must not be PC.
Condition flags
This instruction does not change the flags.
Examples
MRS R0, PRIMASK ; Read PRIMASK value and write it to R0
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