6.38 __get_SP Intrinsic Function

Returns the value of the stack pointer register (R13).

The function reads the Main Stack Pointer (MSP) value using the instruction MRS. 

Physically two different stack pointers (SP) exist:

• The Main Stack Pointer (MSP) is the default stack pointer after reset. It is also used when running exception handlers (handler mode).
• The Process Stack Pointer (PSP), which can be used only in thread mode.

Register R13 banks the SP. The SP selection is determined by the bit[1] of the CONTROL register:

• =0 MSP is the current stack pointer. This is also the default SP. The initial value is loaded from the first 32-bit word of the vector table from the program memory.
• =1 PSP is the current stack pointer. The initial value is undefined.

unsigned int __get_SP(void);

__get_MSP();