I want to generate a rand series which diff with diff seed ;
task automatic test_rand();
for(int i=0;i<32;i++) begin
$display("rand test1 : %h",$urandom &8'hff);
$display("rand test2 : %h",$urandom(98));
$display("rand test 10: %h",{$random()}%10);
$display("urand test : %h",$urandom_range(32));
end
endtask
test1 always be ‘df’ except the first one
and test always be ‘d’
result:
The argument to $urandom is the seed value. This argument is optional, but when you set it to a fixed value, such as 98, you force the simulator to return the same random number from $urandom.
Instead of $urandom(98), just omit the 98:
$display("rand test2 : %h",$urandom());
In reply to gsulliva:
$display("rand test2 : %h",$urandom());
get the same rand series when I run the case next time;
I want to get a new rand series different each time when run the case, how to deal with it
In reply to designer007:
SystemVerilog has a default initial random seed that can be set from the tool command line. (Questa has -sv_seed random). This applies to $urandom but not $random. See section 18.14 Random stability in the IEEE 1800-2017 SystemVerilog LRM
-sv_seed random used as
vsim -sv_seed random
or
vsim -sv_seed a_specific_number
?
In reply to dave_59:
In reply to designer007:
SystemVerilog has a default initial random seed that can be set from the tool command line. (Questa has -sv_seed random). This applies to $urandom but not $random. See section 18.14 Random stability in the IEEE 1800-2017 SystemVerilog LRM
In reply to designer007:
You typically use a random seed each time you run a testcase. To debug a testcase failure, you use a specific number to repeat the same series of random numbers generated for that seed.
In reply to dave_59:
In reply to designer007:
You typically use a random seed each time you run a testcase. To debug a testcase failure, you use a specific number to repeat the same series of random numbers generated for that seed.
I try vsim -sv_seed random 2 times;
task automatic test_rand();
for(int i=0;i<32;i++) begin
$display("rand test1 : %h seed: %h",$urandom, $get_initial_random_seed );
$display("rand test2 : %h",$urandom(98));
$display("rand test 10: %h",{$random()}%10);
$display("urand test : %h",$urandom_range(32));
end
endtask
but rand test1 result is same , with diff seed
1st rst:
2nd rst:
In reply to designer007:
I’m not seeing that. Here is a complete example
module top;
task automatic test_rand();
for(int i=0;i<2;i++) begin
$display("rand test1 : %h seed: %h",$urandom, $get_initial_random_seed );
$display("rand test2 : %h",$urandom(98));
$display("rand test 10: %h",{$random()}%10);
$display("urand test : %h",$urandom_range(32));
end
endtask
initial test_rand;
endmodule
1st run
# rand test1 : 098cdb2e seed: 0f32c20e
# rand test2 : a208270a
# rand test 10: 00000008
# urand test : 0000000f
# rand test1 : f0982ece seed: 0f32c20e
# rand test2 : a208270a
# rand test 10: 00000007
# urand test : 0000000f
2nd run
# rand test1 : 4442eba1 seed: 09f2d430
# rand test2 : a208270a
# rand test 10: 00000008
# urand test : 0000000f
# rand test1 : f0982ece seed: 09f2d430
# rand test2 : a208270a
# rand test 10: 00000007
# urand test : 0000000f
In reply to dave_59:
yes , it’s correct ;
something tricky happened in my env ;
I find a way to work around