The Cortex-M4 processor
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2.1.3 
Core registers 
Figure 2. Processor core registers
          
Table 2. Summary of processor mode, execution privilege level, and stack usage
Processor
mode
Used to
execute
Privilege level for
software execution
Stack used
Thread
Applications
Privileged or unprivileged (1)
1.
See CONTROL register on page 25.
Main stack or process stack (1)
Handler
Exception handlers
Always privileged
Main stack
Table 3. Core register set summary 
Name
Type (1)
Required
privilege (2)
Reset
value
Description
R0-R12
read-write
Either
Unknown
General-purpose registers on page 19
MSP
read-write
Privileged
See description Stack pointer on page 19
PSP
read-write
Either
Unknown
Stack pointer on page 19
LR
read-write
Either
0xFFFFFFFF
Link register on page 19
PC
read-write
Either
See description Program counter on page 19