Implementation

The CodeWarrior for DSP56800E and DSP56800EX has intrinsic functions to generate inline-assembly-language instructions. These intrinsic functions are a CodeWarrior extension to ANSI C.

Use intrinsic functions to target specific processor instructions. For example:

• Intrinsic functions let you pass in data for specific optimized computations. For example, ANSI C data-representation rules may make certain calculations inefficient, forcing the program to jump to runtime math routines. Such calculations would be coded more efficiently as assembly language instructions and intrinsic functions.
• Intrinsic functions can control small tasks, such as enabling saturation. One method is using inline assembly language syntax, specifying the operation in an asm block, every time that the operation is required. But intrinsic functions let you merely set the appropriate bit of the operating mode register.

The IDE implements intrinsic functions as inline C functions in file intrinsics_56800E.h, in the MSL directory tree. These inline functions contain mostly inline assembly language code. An example is the abs_s intrinsic, defined as:

#define    abs_s(a) __abs_s(a)

           /* ABS_S */

inline Word16 __abs_s(register Word16 svar1)

{

/*

 *   Defn: Absolute value of a 16-bit integer or fractional value

 *        returning a 16-bit result.

 *        Returns $7fff for an input of $8000

 *   

 *   DSP56800E instruction syntax:  abs FFF

 *             Allowed src regs:  FFF

 *             Allowed dst regs:  (same)

 *   

 *   Assumptions: OMR's SA bit was set to 1 at least 3 cycles

 *   before this code.

 */

   asm(abs svar1);

   return svar1;

}