Execution flow of randsequence statement

UVM
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1

I am attempting to create a test scenario reflecting a state transition diagram. In my case, there is no single defined path from start to end and there are almost 30+ unique paths that could be generated from the state transition diagram. So I assumed that randsequence would help me out in this situation and implemented the same within the base test (derived from UVM base test).
Below is a shortened illustration similar to my code,

task run_phase();
//
//
randsequence(main)
main: A 
A   : execute_A B;
B   : execute_B C;
C   : execute_C D|E;
D   : execute_D A;
E   : execute_E F;
F   : execute_F;
// execute_* are all terminals that contain just display statements for now
// execute_F contains the break statement to exit out of the randsequence
endsequence
endtask

One of the generated output that contradicts my expectation is,
A B D …
Question: In B, I expected execute_B and C to get executed in that order always. But I see it does not happen at times, and the execution seems to land upon an unexpected state transition.
Please clarify.

Thanks,
Manju

2

In reply to manjuP:

Hi Manju,
The code below seems to be a solution to your problem.
The problem with your code may be that, while solving the sequence the simulator is selecting
either (execute_C, D) or (E) for execution. So, whenever (E) is selected (execute_C) is not going to be executed.
So, if you want (execute_C) to be always executed after (B), you can correct your code as shown below.

module test;
  
task my_test();

randsequence(main)
	main: A;
    A   : execute_A B;
    B   : execute_B C;
    C   : execute_C D | execute_C E;
    D   : execute_D A;
    E   : execute_E F;	
    F   : execute_F;
    execute_A : {$display("execute_A");};
    execute_B : {$display("execute_B");};
    execute_C : {$display("execute_C");};
    execute_D : {$display("execute_D");};
    execute_E : {$display("execute_E");};
    execute_F : {$display("execute_F");};
endsequence
endtask

initial begin
  my_test;
end
endmodule

Regards,
Mohit