Intel® High Level Synthesis Compiler Pro Edition: Best Practices Guide

ID 683152
Date 12/13/2021
Public

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7.3.2. Example: Merging Memories Width-Wise

Use the hls_merge("<mem_name>","width") attribute to force the Intel® HLS Compiler Pro Edition to implement variables in the same memory system, merging their memories by width.

All variables with the same <mem_name> label set in their hls_merge attributes are merged.

Consider the following component code:

component short width_manual (int raddr, int waddr, short wdata) {

  short a[256];
  short b[256];

  short rdata = 0;
  
  // Lock step write
  a[waddr] = wdata;
  b[waddr] = wdata;

  // Lock step read 
  rdata += a[raddr];
  rdata += b[raddr];

  return rdata;
}
Figure 39. Implementation of Local Memory for Component width_manual

In this case, the Intel® HLS Compiler Pro Edition can coalesce the load and store instructions to local memories a and b because their accesses are to the same address, as shown below.

component short width_manual (int raddr, int waddr, short wdata) {

  short a[256] hls_merge("mem","width");
  short b[256] hls_merge("mem","width");

  short rdata = 0;
  
  // Lock step write
  a[waddr] = wdata;
  b[waddr] = wdata;

  // Lock step read 
  rdata += a[raddr];
  rdata += b[raddr];

  return rdata;
}
Figure 40. Width-Wise Merge of Local Memories for Component width_manual

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