5.5.1. angel_SWIreason_EnterSVC (0x17)

Sets the processor to Supervisor (SVC) mode and disables all interrupts by setting both interrupt mask bits in the new CPSR. With RealMonitor, Angel, or Multi-ICE, the User stack pointer (r13_USR) is copied to the Supervisor stack pointer (r13_SVC) and the I and F bits in the current CPSR are set, disabling normal and fast interrupts.


If debugging with ARMulator:

  • r0 is set to zero indicating that no function is available for returning to User mode

  • the User mode stack pointer is not copied to the Supervisor stack pointer.


Register r1 is not used. The CPSR can specify User or Supervisor mode.


On exit, r0 contains the address of a function to be called to return to User mode. The function has the following prototype:

void ReturnToUSR(void)

If EnterSVC is called in User mode, this routine returns thecaller to User mode and restores the interrupt flags. Otherwise, the action of this routine is undefined.

If entered in User mode, the Supervisor stack is lost as a result of copying the user stack pointer. The return to User routine restores r13_SVC to the Angel Supervisor mode stack value, but this stack must not be used by applications.

After executing the SWI, the current link register will be r14_SVC, not r14_USR. If the value of r14_USR is required after the call, it must be pushed onto the stack before the call and popped afterwards, as for a BL function call.

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