Declare vector size with expression from generate variable

Question

So I am trying to declare a variable sized array based on a generate variable, but my linting tool SpyGlass complains about rule BitOrder-ML and gives the following error message:

Declare 'Vector Size' bit order '[((1 << level) -1):0]' as per convention

This is the code that generates the problem:

genvar level;
localparam integer LEVELS = 3;
generate
   for (level=0; level<LEVELS; level=level+1) begin
      wire result[(1 << level)-1:0];
   end
endgenerate

Is SpyGlass sane here? Does it somehow think that the expression (1 << level)-1 would generate to a negative value?

The synthesize completes without a problem when the error is waived.

what will be the result for level == 0? you will get the result[-1:0] i would not blame spyglass for that. — Serge
– Serge, Commented Jul 21, 2017 at 13:26

Ariyan Sharifi · Accepted Answer · 2017-07-21 15:01:58Z

1

first of all

1-you have syntax problem

wire result[(1 << level)-1:0]]; you should delete last ].

2-you should declare level as a genvar not integer! genvar level; is correct.

NOTE : [(2^level)-1:0] is more regular than [(1 << level)-1:0]

edited Jul 21, 2017 at 15:01

answered Jul 21, 2017 at 14:36

Ariyan Sharifi

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3 Comments

Moberg Over a year ago

Sorry, typos. Fixed the code. I can add that the code synthesize fine if i turb off linting of these lines.

Ariyan Sharifi Over a year ago

I use ISE xilinx syntheses tool below code and it have no problem can U upload your full code to i check it?

Moberg Over a year ago

It's the linting tool spyglass and also nlint that has problem with the code. The code is fine otherwise and able to synth.

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