The problem I'm facing is closely related to this: https://electronics.stackexchange.com/a/540545/238188 . I found I could not simulate a T Flip-Flop without a reset on Multisim Live.
I found that I could not get a T Flip-Flop without a reset to simulate in SystemVerilog either, but I could get a JK Flip-Flop without a reset to simulate. This is because I can set a JK Flip-Flop to a known state using J = 0, K = 1 or K = 1, J = 0.
The design code:
module t_ff(input logic t, clk, output logic q, q_bar); parameter HOLD = 1'b0, TOGGLE = 1'b1; always_ff @(posedge clk) case (t) HOLD: q <= q; TOGGLE: q <= ~q; default: q <= 1'bz; endcase assign q_bar = ~q; endmodule
I tried using
bit in the testbench, but that did not work either (just as I expected). I understand that a reset is important for a Flip-Flop in IC Design, but can't we build a Flip-Flop without a reset? I think the T Flip-Flop can be used without a reset in applications when the input for the flip-flop comes from another digital circuit.
I also came across this question and answer: Is there a right way of implementing a T flip flop in verilog wrt using reset signal?
But that answer does not mention what should be done if we don't use a reset.
My question arises from this conversation I had with user "Elliot Alderson"
@ElliotAlderson if you design a T Flip-Flop where the only inputs are T and the clock, then there is no way to set the output to a known state in simulation that supports 'X'. Further reading: sutherland-hdl.com/papers/… – Shashank V M Jan 3 at 16:32
@ShashankVM I think you can, with an initial block in Verilog for example. Sutherland writes very useful papers...did you read the first sentence of the second paragraph in Section 7? – Elliot Alderson Jan 3 at 17:42 (Why can't I make flip-flops in logic simulators?)
"Elliot Alderson" says we can use an initial block to set the output to a known state. I followed that comment and read the section of that paper by Sutherland. I found it seems possible according to the paper, but how is it done?
Link to the paper: https://sutherland-hdl.com/papers/2013-DVCon_In-love-with-my-X_paper.pdf
How is this problem handled in Gate-level simulations?