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SystemVerilog Regions

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Overview

SystemVerilog's concept of "Scheduling Regions" is a crucial element influencing the execution flow of hardware designs. These regions determine the order of process and statement execution, impacting simulation behavior and final hardware implementation. Understanding scheduling regions empowers hardware engineers to optimize designs for performance, avoid pitfalls, and seamlessly integrate with various tools and verification methods. By grasping the fundamental aspects of SV Regions, designers can create efficient and robust HDL/HVL codes. Given below is a basic flow of the execution using the SV scheduling regions.

To better understand how regions work, you can review the verilog regions page using the following link.

Verilog Regions

Following is a diagram about the SystemVerilog regions for better pictorial understanding.

SystemVerilog Scheduling Regions

In SystemVerilog, along with Verilog regions, additional "Program Block" execution regions must also be considered. Any code which you wish to run in "Re-Regions" of SV, must be coded inside the program block. More can be found about this block in the next section.

Theory Questions
    Re-Active, Re-Inactive and Re-NBA.
    This is the region where the assertions are evaluated based on the preponed region sampled values of all the involved variables.
    Pre-Poned Region 
    module top;
    initial
    begin
        $display( "A" );    
    end
endmodule

program pp;
    initial
    begin
        $display( "B" );    
    end
endprogram

    module top;
    initial
    begin
        $display( "A" );    
    end
endmodule

program pp;
    initial
    begin
        #0;
        $display( "B" );    
    end
endprogram
Coding Questions 
    integer NUM = 10; // Global Variable Accessible TO Both Verilog Top Block and SystsemVerilog Program Block

program top_p;
  
  
  initial
  begin
    $display( "%d | Post NBA Region Value", NUM );
    
    NUM = 100;
    
    NUM <= 50; // Will update the RHS in NBA
    
    $display( "%d | Re-Active Region", NUM );
  end
  
  initial
  begin
    #0;
    NUM = 70;
    $display( "%d | Re-Inactive Region (because of the #0)", NUM );
  end
  
  initial
  begin
    #1;
    $display( "%d | After Re-NBA Region (printing this in the next time step)", NUM );
  end
  
endprogram

module top;
  
  initial
  begin
    NUM <= 30; // Will update the RHS in NBA
    
    $display( "%d | Active Region", NUM );
  end
  
  initial
  begin
    #0;
    NUM = 20;
    $display( "%d | Inactive Region (because of the #0)", NUM );
  end
  
endmodule