constraint
In reply to surya narayana Gutha:
There can be 2 ways of doing it , one is having the logic in post_randomize function . And other one is having logic in constraint .Find below the example
Code :
rand bit[31:0] dummy; //Logic in post randomize
rand bit[31:0] dummy1; // Logic in constraint
function void post_randomize();
for(int i =0;i<16;i++)
begin
dummy[31-i] = dummy[i];
end
endfunction
constraint range {
foreach(dummy[j])
dummy1[j] == dummy1[31-j];}
Output :
1st iteration :
dummy = 10110010000101111110100001001101
dummy1 = 10110111101001111110010111101101
2nd iteration :
dummy= 11010000000111100111100000001011
dummy1 = 00111000101010011001010100011100
1 Like
In reply to nikhilverif:
Now that you’ve given the interview/homework problem away, here’s the simple version:
constraint palindrome { dummy2 == {<<{dummy2}}; }
Ref: 11.4.14.2 Re-ordering of the generic stream
1 Like
Hi Dave,
I see below error if I use streaming operators in constraints.
Error-[IUSO] Incorrect use of streaming operators
testbench.sv, 7
$unit, “{ << 1 {this.data}}”
Streaming operators cannot be used in this context
Hi @dave_59 I am also getting same error as @VarunVlsi mentioned.
CODE :
class A;
rand bit[31:0] dummy; //Logic in post randomize
rand bit[31:0] dummy1; // Logic in constraint
rand bit[31:0] dummy2; // Logic in constraint
function void post_randomize();
for(int i =0;i<16;i++)
begin
dummy[31-i] = dummy[i];
end
endfunction
constraint range {
foreach(dummy1[j])
dummy1[j] == dummy1[31-j];}
constraint palindrome { dummy2 == {<<{dummy2}}; }
endclass
module AA;
A a;
initial begin
a = new();
a.randomize();
$display(" dummy = %b", a.dummy);
$display(" dummy = %b", a.dummy1);
end
endmodule
Simulation output result:
Error-[IUSO] Incorrect use of streaming operators
testbench.sv, 21
$unit, “{ << 1 {this.dummy2}}”
Streaming operators cannot be used in this context
Error-[ETRFS] Explicit typecast required for streams
testbench.sv, 21
$unit, “(this.dummy2 == { << 1 {this.dummy2}})”
Stream operands require explicit typecast to be used with other operators
And one more thing that @surya_narayana_Guptha said he want palindrome in the form of decimal.
Eg : 59395.
Please suggest us or help us.
Thanks in Adavance.
In reply to VK_18:
A decimal palindrome requires a completely different strategy, probably using binary-coded decimal(BCD)
In reply to dave_59:
Hi, I was trying to make code for decimal base palindrome here. I am able to reverse number but I don’t know
1.) how to reduce length of a to 16 bits, so that total produce result is of 32 bit after concatenation.
Is there any better approach you can suggest? Thanks.
[i]In reply to [url=https://verificationacademy.com/forums/systemverilog/write-
class b;
rand int unsigned a;
rand shortint x,y;
constraint a_c {reverse_num(x)==y;}
constraint xy { a[15:0] == x; a[31:16] == y; }
function shortint unsigned reverse_num(shortint a);
while(a>0) begin
shortint pop_1;
pop_1= a%10;
reverse_num=reverse_num*10 + pop_1;
a =a /10;
end
endfunction
endclass
Hi Dave,
I tried the above code, but not able to see the actual output.
module p1;
class b;
rand int unsigned a;
rand shortint unsigned x,y;
constraint a_c {reverse_num(x)==y;}
constraint xy { a[15:0] == x; a[31:16] == y; }
function shortint unsigned reverse_num(shortint a);
while(a>0) begin
shortint pop_1;
pop_1= a%10;
reverse_num=reverse_num*10 + pop_1;
a =a /10;
end
endfunction
function void post_randomize();
$display("elements %0d %0d %0d", x,y, a);
endfunction
endclass
b obj;
initial begin
obj = new;
obj.randomize();
end
endmodule
==================
output of the code
elements 53412 0 53412
if the input is 53412, output must be 21435.
May I know where do I see the output?
Thank you,
class A;
rand bit[31:0] val;
rand bit[3:0] arr[8];
constraint PALINDROME { foreach(arr[i] )
{
if( i < (8/2) )
{ arr[i] == arr[(8-1)-i]; }
arr[i] inside {[0:9]}; // For BCD. Can comment it for Hex values
}
}
constraint VALUE { foreach(arr[i] )
{
val[4*i+:4] == arr[i];
}
}
endclass
A a1;
initial begin
a1 = new();
repeat(6) begin
if( a1.randomize() )
$display("Success with %0h_%0h_%0h_%0h_%0h_%0h_%0h_%0h",
a1.val[31:28],a1.val[27:24],a1.val[23:20],a1.val[19:16],a1.val[15:12],a1.val[11:8],a1.val[7:4],a1.val[3:0]);
end
end
2 Likes
Thank You, it was helpful.
Dave,
I tried your approach with following changes within the subroutine
class b;
rand int unsigned val;
rand shortint unsigned x,y;
constraint a_c { reverse_num(x) == y; }
constraint xy { val[15:0] == x; val[31:16] == y; }
function bit[15:0] reverse_num(bit[15:0] a);
reverse_num = { <<4{a} } ;
endfunction
endclass
b a1;
initial begin
a1 = new();
repeat(6) begin
if( a1.randomize() )
$display("Success with %0h_%0h_%0h_%0h_%0h_%0h_%0h_%0h",
a1.val[31:28],a1.val[27:24],a1.val[23:20],a1.val[19:16],a1.val[15:12],a1.val[11:8],a1.val[7:4],a1.val[3:0]);
end
end
However when testing with random seeds I observe that one of the tools ( VCS ) throws constraint failure.
I am not clear on the reason behind the failure , would like to hear your thoughts on the same
Works for me. I cannot see why it would fail.
Hi Dave,
I tried using streaming operator directly without calling the function in constraint
class b;
rand int unsigned val;
constraint palindrome { val[31:16] == { << 4 { val[15:0] } } ; }
endclass
b a1;
initial begin
a1 = new();
repeat(6) begin
if( a1.randomize() )
$display("Success with %0h_%0h_%0h_%0h_%0h_%0h_%0h_%0h",
a1.val[31:28],a1.val[27:24],a1.val[23:20],a1.val[19:16],a1.val[15:12],a1.val[11:8],a1.val[7:4],a1.val[3:0]);
end
end
Unfortunately the code doesn’t compile.
Wouldn’t the return type of { << 4 { val[15:0] } } be a 16-bit packed value ?
Could I add any cast to make the code work ?
Hi,
I have made few changes, now code is working fine.
class b;
rand int unsigned val;
rand shortint unsigned x;
constraint xy { val == reverse_num(x); }
function bit[31:0] reverse_num(bit[15:0] x);
reverse_num = {{ <<4{x} },x} ;
endfunction
endclass
module tb;
b a1;
initial begin
a1 = new();
repeat(6) begin
if( a1.randomize() )
$display("Success with %0h_%0h_%0h_%0h_%0h_%0h_%0h_%0h",
a1.val[31:28],a1.val[27:24],a1.val[23:20],a1.val[19:16],a1.val[15:12],a1.val[11:8],a1.val[7:4],a1.val[3:0]);
end
end
endmodule
Success with d_2_1_d_d_1_2_d
Success with 6_e_6_5_5_6_e_6
Success with 1_8_0_6_6_0_8_1
Success with 2_a_1_3_3_1_a_2
Success with 4_2_0_6_6_0_2_4
Success with 6_b_8_c_c_8_b_6