MSP430 IAR C/C++ Compiler reference guide - Rice University

Assembler language interfaceRegisters used for returning valuesThe registers available for returning values are:Return values8-bit values16-bit values32-bit values64-bit valuesTable 24: Registers used for returning valuesPassed in registersR12R12R13:R12R15:R14:R13:R12Stack layoutIt is the responsibility of the caller to clean the stack after the called function hasreturned.Return value pointerIf a structure is returned, the caller passes a pointer to a location where the calledfunction should write the result. The pointer should be passed in the register R12.The called function must return the pointer in the register R12.EXAMPLESThe following section shows a series of declaration examples and the correspondingcalling conventions. The complexity of the examples increases towards the end.Example 1Assume that we have the following function declaration:int add1(int);This function takes one parameter in the register R12, and the return value is passed backto its caller in the register R12.The following assembler routine is compatible with the declaration; it will return a valuethat is one number higher than the value of its parameter:ADD.WRETA#1,R12; For the MSP430X architecturePart 1. Using the compiler95