Texas Instruments TMS320C64X manual Calling a Dsplib Function From C

Using DSPLIB

2.2.2Calling a DSPLIB Function From C

In addition to correctly installing the DSPLIB software, follow these steps to include a DSPLIB function in the code:

-Include the function header file corresponding to the DSPLIB function

-Link the code with dsp64plus.lib

-Use a correct linker command file for the platform used.

The examples in the DSP\Examples folder show how to use the DSPLIB in a Code Composer Studio C envirionment.

2.2.3Calling a DSP Function From Assembly

The C64x+ DSPLIB functions were written to be used from C. Calling the functions from assembly language source code is possible as long as the calling function conforms to the Texas Instruments C64x+ C compiler calling conventions. For more information, see Section 8 (Runtime Environment) of TMS320C6000 Optimizing C Compiler User’s Guide (SPRU187).

2.2.4DSPLIB Testing − Allowable Error

DSPLIB is tested under the Code Composer Studio environment against a reference C implementation. You can expect identical results between Reference C implementation and its Assembly implementation when using test routines that focus on fixed-point type results. The test routines that deal with floating points typically allow an error margin of 0.000001 when comparing the results of reference C code and DSPLIB assembly code.

2.2.5DSPLIB Overflow and Scaling Issues

The DSPLIB functions implement the same functionality of the reference C code. You must conform to the range requirements specified in the API function, and in addition, restrict the input range so that the outputs do not overflow.

In FFT functions, twiddle factors are generated with a fixed scale factor; i.e., 32767(=215−1) for all 16-bit FFT functions, 1073741823(=230−1) for DSP_fft32x32s, 2147483647(=231−1) for all other 32-bit FFT functions. Twiddle factors cannot be scaled further to not scale input data. Because DSP_fft16x16r and DSP_fft32x32s perform scaling by 2 at each radix-4 stage, the input data must be scaled by 2(log2(nx)−cei[log4(nx)−1]) to completely prevent overflow. In all other FFT functions, the input data must be scaled by 2(log2(nx)) because no scaling is done by the functions.

2-4