Compare processor modes between Cortex-m & -a

Common executing mode

Both Cortex-M33 & A9 processor support two executing mode. (code execution)

• Privileged mode
  • Privileged execution has access to all resources available to the security state
  • All resources => Banked registers in the System Control Space
• Unprivileged mode
  • Unprivileged execution limits or excludes access to some resources appropriate to the current security state
  • Some resources => registers

Cortex-m33: Modes of operation and execution

The Cortex-M33 processor supports two operating modes.

• Thread operating mode
  • Condition
    • The processor enters Thread mode on reset
    • As a result of an exception return
  • Privileged and Unprivileged code can run
• Handler operating mode
  • Condition
    • As a result of an exception return
  • All code is privileged in Handler mode

Cortex-A9: ARMv7-A; ARM processor modes

The Cortex-A9 processor supports eight processor modes.

• User(Unprivileged): Execute application code
• FIQ: Entered as a result of a fast interrupt
• IRQ: Entered as a result of a normal interrupt
• Supervisor:
  • Execute kernel code
  • Entered on Reset
  • Execution of a Supervisor Call (SVC) instruction; System Call
• Monitor:
  • A Secure mode that enables change between Secure and Non-secure states
  • Entered on execution of a Secure Monitor Call (SMC) instruction
• Abort: Entered as a result of a Data Abort exception or Prefetch Abort exception
• Undefined: Entered as a result of an instruction-related error
• System: Application code that requires privileged access