pragma HLS disaggregate - 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

Description

The DISAGGREGATE pragma lets you deconstruct a struct variable into its individual elements. The number and type of elements created are determined by the contents of the struct itself.

Important: Structs used as arguments to the top-level function are aggregated by default, but can be disaggregated with this directive or pragma. Refer to AXI4-Stream Interfaces for important information about disaggregating structs associated with streams.

Syntax

Place the pragma in the C source within the boundaries of the region, function, or loop.

#pragma HLS disaggregate variable=<variable>

Options

Where:

  • variable=<variable>: Specifies the struct variable to disaggregate.

Example 1

The following example shows the struct variable a in function top will be disaggregated:

#pragma HLS disaggregate variable=a

Example 2

Disaggregated structs can be addressed in your code by the using standard C/C++ coding style as shown below. Notice the different methods for accessing the pointer element (a) versus the reference element (c);

struct SS
{
  int x[N];
  int y[N];
};
  
int top(SS *a, int b[4][6], SS &c) {
#pragma HLS disaggregate variable = a
#pragma HLS interface s_axilite port = a->x
#pragma HLS interface s_axilite port = a->y
  
// Following is now supported
#pragma HLS disaggregate variable = c
#pragma HLS interface ap_memory port = c.x
#pragma HLS interface ap_memory port = c.y