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  • Range must be bounded by constant expressions

Range must be bounded by constant expressions

SystemVerilog 4159
ssingh
ssingh
Forum Access
38 posts
February 01, 2013 at 5:21 am

I am trying to implement the following in systemverilog.

always_comb
    begin
	for(int i=0;i<=124;i=i+6)
	    begin
	        offset = DFF_data[ ((2*i)+1):(2*i) ]; // Error !	
		data_output[i+offset]= data_input[i];
	    end
   end

I get the following error in the line marked above: Range must be bounded by constant expressions. I can see the error ocuurs beacuse of the use of "i" in defining the range of array DFF_data. But writing this without "i" seems impractical. I am using QuestaSim 10.1d. Has anyone come across such a situation?

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Solution

Solution

dave_59
dave_59
Forum Moderator
7419 posts
February 01, 2013 at 7:41 am

Verilog integral expressions must have a constant width determined at compile time.

Use need to use a indexed part-select which allows you to specify a variable base expression with a constant width. (this comes from Verilog)

logic [15:0] down_vect;
logic [0:15] up_vect;
down_vect[lsb_base_expr +: width_expr]
up_vect[msb_base_expr +: width_expr]
down_vect[msb_base_expr -: width_expr]
up_vect[lsb_base_expr -: width_expr]

So you can write

offset = DFF_data[ (2*i) +: 1 ];

- Dave Rich

ssingh
ssingh
Forum Access
38 posts
February 05, 2013 at 4:27 am

In reply to dave_59:

Thank you

vishalkewlani
vishalkewlani
Full Access
6 posts
February 10, 2015 at 11:23 pm

In reply to ssingh:

Thank you very much

raja.kuraku
raja.kuraku
Full Access
16 posts
June 01, 2015 at 5:32 am

In reply to vishalkewlani:

Hello Guys,

I am facing the same problem with 2variables.

offset = DFF_data[ ((2*j)+7):(2*i) ];

Here i am having the 2 variables i&j.
So how to do part select.
Means to say that my width will vary.

Please answer the question.

dave_59
dave_59
Forum Moderator
7419 posts
June 01, 2015 at 8:33 am

In reply to raja.kuraku:

You can use a shift and mask operation

offset = (DFF_data >> 2*i) & 2**(width)-1

I'll leave it to you or someone else to figure out the width expression and make sure I have the right operator precedence.

- Dave Rich

saroj kumar sahoo
saroj kumar sahoo
Full Access
2 posts
January 09, 2018 at 10:21 pm

In reply to dave_59:

module wr_strb;
bit [15:0] Data = 'hFFFF;
bit [15:0] WDATA;
 
task strobe(int r);
WDATA[(4*r-1):0] = 'hx;
WDATA[15:(4*r)] =  Data[15:(4*r)];
$display("WDATA = %0h",WDATA);
endtask
 
initial
begin
strobe(2);
end
endmodule

********************************************************************************
Hi Dave,
i'm getting an error : "Range must be bounded by constant expression" for the above code.
If you have any solution for this please guide me.

thanks and regards,
Saroj Kumar Sahoo

dave_59
dave_59
Forum Moderator
7419 posts
January 10, 2018 at 10:46 am

In reply to saroj kumar sahoo:

function void strobe(int r);
  bit [15:0] mask;
  mask = (15'b1 << 4*r) - 1;
  WDATA =  Data ^ (mask & 15'hXXXX);
  $display("WDATA = %0h",WDATA);
endfunction

- Dave Rich

saroj kumar sahoo
saroj kumar sahoo
Full Access
2 posts
January 11, 2018 at 5:15 am

In reply to dave_59:

Thank you very much Dave.

mansi m joshi
mansi m joshi
Forum Access
5 posts
August 08, 2018 at 10:30 pm

data_in[7*(j+1)+j:8*j] // while i am doing this in sv this error comes----> Range must be bounded by constant expressions how to get the same functionality

dave_59
dave_59
Forum Moderator
7419 posts
August 09, 2018 at 12:03 am

In reply to mansi m joshi:
data_in[j+:8]

- Dave Rich

mansi m joshi
mansi m joshi
Forum Access
5 posts
August 09, 2018 at 12:21 am

hello dave in this above example if only 8 bit slicing needs for ex : [7:0] [15:8] [23:16] [31:24] [39:32] [47:40] [55:48] [63:56] and so on

mansi m joshi
mansi m joshi
Forum Access
5 posts
August 09, 2018 at 1:46 am

its done by using this : data_in[8*(j):8]

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