1 Reply Latest reply on Aug 12, 2020 1:00 PM by ChRe_4711096

    Simple arbiter not triggering a mockup coprocessor (PWM timer)


      I'm trying to design a simple arbiter that cycles through 4 enable signals that come from 4 different internal sources:

      • the enable signals are multiplexed with a selection index (sel_out[1:0])
      • if the selected enable signal is high, the selection index is kept stable and a coprocessor is triggered (cp_start) to start working for the selected enable source
      • the arbiter then waits for a pulse on cp_done before counting is resumed on sel_out

      Anmerkung 2020-08-12 134256.png

      • State_0 was inserted to avoid an off-by-one error on sel_out
      • sel_int is used to output sel_out
      • cp_done is generated by checking if the state machine is in that state:

      Anmerkung 2020-08-12 134522.png

      For now I'm using a one-shot timer to roughly mimic the coprocessor's behavior. cp_start starts the timer, and the timer's overflow output signals cp_done:

      Anmerkung 2020-08-12 134756.png

      Apparently the timer is never started, so the arbiter never receives a "done" pulse. Incrementing the selection index and keeping it stable once the button is pressed seems to work. Where am I making a mistake here?


      Also, is there a more efficient way to achieve the desired behavior?


      The project is attached.

        • 1. Re: Simple arbiter not triggering a mockup coprocessor (PWM timer)

          It seems to be a problem with the PWM timer. I created a small datapath based dummy coprocessor which

          • waits for a start trigger
          • counts down from 100 to zero
          • generates an output trigger

          Anmerkung 2020-08-12 214953.png


          and with that, the arbiter waits for the coprocessor to complete its task, and then resumes cycling through the en inputs. What my dev board now does is

          • flash the green LED every time sel_out==0
          • on the press of the button: sel_out cycling is stopped when sel_out==0, so green LED stays on
          • red LED turns on for a second while the coprocessor is busy
          • resume cycling (flashing green LED)


          The now working project is attached, but the question why the PWM timer was not starting (see initial post) still remains.