pragma HLS disaggregate - 2021.1 English

Vitis High-Level Synthesis User Guide (UG1399)

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2021.1 English


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.


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

#pragma HLS disaggregate variable=<variable>



  • 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