Datasheet

Semihosting

5.5 Debug agent interaction SWIs

In addition to the C library semihosted functions described in Semihosting SWIs on

page 5-11, the following SWIs support interaction with the debug agent:

• The ReportException SWI. This SWI is used by the semihosting support code as

a way to report an exception to the debugger.

• The EnterSVC SWI. This SWI sets the processor to Supervisor mode.

• The reason_LateStartup SWI. This SWI is obsolete and no longer supported.

These are described below.

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.

Note

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.

Entry

Return

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 the caller 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.