Constraint for selection of Address Bits based on strobe bits

SystemVerilog
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1

Hi everyone, I am pretty much new in SV. I am trying write a constraint, based on strobe and valid bit, particular bits of address bits will be valid and printed. But as I understand in SV Queues, we can’t assigning in queue unless we define it. How can we achieve the intention which I mentioned here in code?


class packet;
  bit [63:0] address;
  bit [7:0]  strobe;
  bit [7:0]  data[$];
  bit valid;
  
  constraint c1 {
    if (strobe==0 && valid==1)
      data = address[7:0];
    else if (strobe==1 && valid==1)
     data = address[15:8];
    else if (strobe==2 && valid==1)
      data = address[23:16];
    else if (strobe==3 && valid==1)
      data = address[24:30];
    else if (strobe==4 && valid==1)
      data = address[38:31];
    else if (strobe==5 && valid==1)
      data = address[39:47];
    else if (strobe==6 && valid==1)
      data = address[48:55];
    else if (strobe==7 && valid==1)
      data = address[56:63];
    else;                  }
endclass`
      
module TB;
  packet pkt;
  pkt = new();
  
  initial begin
    address = 'h1234_45678_9ABC_DEF10;
    strobe = 1;
    valid =1;
    $display("Address:%0h, Strobe:%0h, Valid:%0d, VALID_DATA:%0h", address, strobe, valid, pkt.data[]);    
  end
endmodule

Thanks and Regards,

2

In reply to skyhome0911:


//data size will be 8 . wherever the strobe is selected use mask, otherwise set to zero .
class packet;
  rand bit [63:0] address;
  rand bit [7:0]  strobe;
  rand bit [7:0]  data[8];
  bit valid;
  bit [15:0] mask = 'hff ;
 
  constraint c1 { 
   foreach(strobe[i]){
      if(strobe[i])
      data[i] == ((address & (mask << i*8)) >> i*8); // shift left to use the lower byte assignment 
      else 
      data[i] == 0 ;
   }
}
   
endclass`
3

In reply to kddholak:

Hi kddholak,
Thank you so much for reply and i understood your logic as well which is way more optimized and more correct way of doing. But, I need help in the way I am trying to implement so as to clear my few concepts about queues and its assignment. Could you please help me out in my logic formation?

Thanks and Regards,

4

In reply to skyhome0911:

It would help to explain with a few example of what results you are looking for. Constraints are used for random values, yet you never declared and rand members or called randomize(). Why is data declared as a queue if you only one to write one byte to it?