Enumerated Types - 2021.2 English

Vitis High-Level Synthesis User Guide (UG1399)

Document ID
UG1399
ft:locale
English (United States)
Release Date
2021-12-15
Version
2021.2 English

The header file in the following code example defines some enum types and uses them in a struct. The struct is used in turn in another struct. This allows an intuitive description of a complex type to be captured.

The following code example shows how a complex define (MAD_NSBSAMPLES) statement can be specified and synthesized.

#include <stdio.h>

enum mad_layer {
 MAD_LAYER_I   = 1,
 MAD_LAYER_II  = 2,
 MAD_LAYER_III = 3
};

enum mad_mode {
 MAD_MODE_SINGLE_CHANNEL = 0,
 MAD_MODE_DUAL_CHANNEL = 1,
 MAD_MODE_JOINT_STEREO = 2,
 MAD_MODE_STEREO = 3
};

enum mad_emphasis {
 MAD_EMPHASIS_NONE = 0,
 MAD_EMPHASIS_50_15_US = 1,
 MAD_EMPHASIS_CCITT_J_17 = 3
};

typedef   signed int mad_fixed_t;

typedef struct mad_header {
 enum mad_layer layer;
       enum mad_mode mode;
 int mode_extension;
 enum mad_emphasis emphasis;

 unsigned long long bitrate;
 unsigned int samplerate;

 unsigned short crc_check;
 unsigned short crc_target;

 int flags;
 int private_bits;

} header_t;

typedef struct mad_frame {
 header_t header;
 int options;
 mad_fixed_t sbsample[2][36][32];
} frame_t;

# define MAD_NSBSAMPLES(header)  \
 ((header)->layer == MAD_LAYER_I ? 12 :  \
 (((header)->layer == MAD_LAYER_III &&  \
 ((header)->flags & 17)) ? 18 : 36))


void types_composite(frame_t *frame);

The struct and enum types defined in the previous example are used in the following example. If the enum is used in an argument to the top-level function, it is synthesized as a 32-bit value to comply with the standard C/C++ compilation behavior. If the enum types are internal to the design, Vitis HLS optimizes them down to the only the required number of bits.

The following code example shows how printf statements are ignored during synthesis.

#include "types_composite.h"

void types_composite(frame_t *frame)
{
 if (frame->header.mode != MAD_MODE_SINGLE_CHANNEL) {
   unsigned int ns, s, sb;
   mad_fixed_t left, right;

   ns = MAD_NSBSAMPLES(&frame->header);
   printf("Samples from header %d \n", ns);

 for (s = 0; s < ns; ++s) {
 for (sb = 0; sb < 32; ++sb) {
 left  = frame->sbsample[0][s][sb];
 right = frame->sbsample[1][s][sb];
 frame->sbsample[0][s][sb] = (left + right) / 2;
 }
 }
 frame->header.mode = MAD_MODE_SINGLE_CHANNEL;
 }
}