The Cortex - M4 processor has the following operation modes during software execution.
• Thread mode - Used to execute application software. The processor enters Thread mode when it
comes out of reset.
• Handler mode - Used to handle exceptions. The processor returns to Thread mode when it has
finished all exception processing.
The privilege levels for software execution are:
• Unprivileged - Unprivileged software executes at the unprivileged level.
The software:
– has limited access to the MSR and MRS instructions, and cannot use the CPS
instruction
– cannot access the system timer, NVIC, or system control block
– might have restricted access to memory or peripherals.
• Privileged
Privileged software executes at the privileged level.
The software can use all the instructions and has access to all resources.
