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

Memory types (MSP430X only)Type definitionsStorage can also be specified using type definitions. The following two declarations areequivalent:typedef char __data20 Byte;typedef Byte *BytePtr;Byte b;BytePtr bp;and__data20 char b;char __data20 *bp;POINTERS AND MEMORY TYPESPointers are used for referring to the location of data. In general, a pointer has a type.For example, a pointer that has the type int * points to an integer.In the MSP430 IAR C/C++ Compiler, a pointer also points to some type of memory. Thememory type is specified using a keyword before the asterisk. For example, a pointerthat points to an integer stored in data20 memory is declared by:int __data20 * p;Note that the location of the pointer variable p is not affected by the keyword. In thefollowing example, however, the pointer variable p2 is placed in data20 memory. In thiscase, p2 points to a character in data16 memory.char __data16 * __data20 p2;For example, the functions in the standard library are all declared without explicitmemory types.Differences between pointer typesA pointer must contain information needed to specify a memory location of a certainmemory type. This means that the pointer sizes are different for different memory types.For the MSP430 IAR C/C++ Compiler, the size of the data16 and data20 pointers are 16and 32 bits, respectively.In the MSP430 IAR C/C++ Compiler, it is illegal to convert a data20 pointer to a data16pointer without an explicit cast.STRUCTURES AND MEMORY TYPESFor structures, the entire object is placed in the same memory type. It is not possible toplace individual structure members in different memory types.18MSP430 IAR C/C++ CompilerReference Guide