CODEWITHSUNDEEP
randomerror-handlingverilogsystem-verilog
Rucha R
Rucha R

Reputation: 33

Random 1-bit and 2-bit error using random in systemverilog

I am making use of an error detction block. I need to randomly flip 1 bit of the data using SystemVerilig. How do I do this? I also want to do the same where I flip 2 random bits of data.

Hamming Code is being used. So random bits from parity and data need to be flipped.

Upvotes: 0

Views: 2879

Answers (2)

Sreejin TJ
Sreejin TJ

Reputation: 337

You can declare a variable with bit-width same as your “data” size. Assuming your “data” size is 8bits(say data_8b), you can declare a temporary variable of size 8bits(say error_inject_8b) and you can use simple EXOR logic to insert multi-bit errors. Refer below snippet 

  error_inject_8b[0] = 1; 
  error_inject_8b[1]  = 1; 
  data_8b = data_8b  ^ error_inject_8b; //injects error in 0th and 1st bits of data

  error_inject_8b = 0;//Reset the errors
  error_inject_8b = $random;
  data_8b = data_8b  ^ error_inject_8b;//Injects error in randomly selected bits

You can also write constraints or randomize with concepts to randomize the error injection based on your requirement.

Upvotes: 0

Mr Bone
Mr Bone

Reputation: 156

The most straightforward way is to use $urandom_range(0, msb) to select which bit you want to corrupt. An example:

module test();

parameter DATA_WIDTH = 29;
parameter IDX_WIDTH = $clog2(DATA_WIDTH);

logic [DATA_WIDTH-1:0] data;
logic [IDX_WIDTH-1:0]  idx_to_flip;

initial begin
   data = $urandom();
   $display("Original data = %x", data);

   idx_to_flip = $urandom_range(0, DATA_WIDTH-1);
   $display("Flipping data bit idx %d", idx_to_flip);

   data[idx_to_flip] = !data[idx_to_flip];
   $display("Corrupted data = %x", data);
end

endmodule

This is very straightforward for a single bit. If you want to corrupt 2 bits, you will need a bit more complexity to ensure the second bit index selected is not the same as the first selected. There are two options for this:

1) Loop over the second $urandom_range() call until it produces a value different than the first random number.

2) Create a class with two 'rand' fields, and use a constraint to ensure the values are not the same:

class Corruption;
  rand bit [IDX_WIDTH-1:0] corrupt_idx1;
  rand bit [IDX_WIDTH-1:0] corrupt_idx2;
endclass

Corruption corr = new;

initial begin
   corr.randomize() with {corrupt_idx1 != corrupt_idx2;};
   $display("Bit indices to flip: %d and %d", corr.corrupt_idx1, corr.corrupt_idx2);
end

Upvotes: 1

Related Questions