# State Machine that drops samples (Problems with return and consume\_each in general\_work)

**URL:** <https://www.ruby-forum.com/t/state-machine-that-drops-samples-problems-with-return-and-consume-each-in-general-work/242865>\
**Category:** GNU Radio\
**Created:** [August 3, 2015, 9:18pm UTC](https://www.ruby-forum.com/t/state-machine-that-drops-samples-problems-with-return-and-consume-each-in-general-work/242865 "2015-08-03T21:18:24Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![Rafa\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/958977/32.png) [@Rafa\_F](https://www.ruby-forum.com/u/Rafa_F)\
**Post date:** [August 3, 2015, 9:18pm UTC](https://www.ruby-forum.com/t/state-machine-that-drops-samples-problems-with-return-and-consume-each-in-general-work/242865/1 "2015-08-03T21:18:24Z")

</div>

Dear all,

I’m trying to implement a simple state machine to receive bursty data  
and  
write it in a file.

To accomplish this I have created a general block that accepts complex  
samples and has two states:

0 - Just drops data. If one of the samples is 0, go to state 1.

1 - Copy inputs to outputs. If one of the samples is 1, go to state 0.

I will use this block in the future to wrap another more complex signal  
processing block that will generate a proper parameter for state  
transition.

However I’m failing to make even this simple one work. Here’s my  
general\_work:

* * *

```
    for (int i = 0; i < noutput_items; i++) {

      currentState = nextState;

      if(in[i] == std::complex<float> (0,0)){

        if(currentState == 0){
          nextState = 1;
          consume_each(i);
          return 0;

        }

        if(currentState == 1){
          for (int j = 0; j < i; j++) {
            out[j] = in[j];
          }
          nextState = 0;
          consume_each(i);
          return i;
        }

      }

    }

    if (currentState == 0){
      consume_each (noutput_items);
      return 0;
    }

    if (currentState == 1){
      for (int j = 0; j < noutput_items; j++) {
        out[j] = in[j];
      }
      consume_each (noutput_items);
      return noutput_items;
    }

```

* * *

Here’s what it does:

1. Receive new state

2. Checks for state transition condition. If true:

2A) If it’s in state 0: Change state to 1, consume all inputs processed  
so  
far (which makes non-processed inputs to go back to the queue in the  
next  
call of general\_work, correct?) and returns 0 (which is equivalent to  
not  
generating outputs, right?)

2B) If it’s in state 1: Same as 2A, but copy ( i ) inputs to the output  
(number of samples before state transition happens) and returns i  
samples.

1. If the loop ends without any state transition, the same thing that  
happened in 2A) and 2B) is executed, however noutput\_items are  
processed/consumed/returned instead.

I’m testing this block in the attached flow graph, however the generated  
file is blank. Both nextState and currentState are private attributes of  
the block and are initialized in the constructor with 0.

My questions are:

1. Am I misunderstanding the way consume\_each and return works?

2. What should I do with the forecast() function? I cannot guarantee  
that  
any numbers of inputs will actually produce an output.

3. Is this really the best way to accomplish what I want?

Thank you all for your assistance,

---

<div class="post-metadata">

**Author:** ![Felipe\_Domingues](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/91b2a8/32.png) [@Felipe\_Domingues](https://www.ruby-forum.com/u/Felipe_Domingues)\
**Post date:** [August 3, 2015, 10:25pm UTC](https://www.ruby-forum.com/t/state-machine-that-drops-samples-problems-with-return-and-consume-each-in-general-work/242865/2 "2015-08-03T22:25:00Z")

</div>

Dear all,

I was able to fix the problem.

Fist I had forecast set to a big number and vector sink was unable to  
provide such amount of inputs. I changed that to  
ninput\_items\_required[0]=  
noutput\_items, not sure if it’s the correct relation thought. But the  
block  
still didn’t work.

Apparently I was not consuming the item responsible for the state  
transition, so general\_work was in an infinite loop. Changing  
consume\_each(i) to consume\_each(i+1) did the trick.

Finally, for some reason I had to delete the blank file generated by  
past  
iterations of the program manually and a correct one was created. Now I  
don’t need to do that any more, but watch out if you are using Ubuntu  
14.04.

Here is the (apparently) working code:

```
    for (int i = 0; i < noutput_items; i++) {

      currentState = nextState;
      std::cout << noutput_items << std::endl;
      std::cout << "\nin[i]: " << in[i] << std::endl;

      if(in[i] == std::complex<float> (0,0)){

        if(currentState == 0){
          std::cout << "\nstatezero" << std::endl;
          nextState = 1;
          consume_each(i+1);
          return 0;

        }

        if(currentState == 1){
          std::cout << "\nstateone" << std::endl;
          for (int j = 0; j < i; j++) {
            out[j] = in[j];
          }
          nextState = 0;
          consume_each(i+1);
          return i;
        }

      }

    }

    if (currentState == 0){
      std::cout << "\nFinishing loop in state zero" << std::endl;
      consume_each (noutput_items);
      return 0;
    }

    if (currentState == 1){

      for (int j = 0; j < noutput_items; j++) {
        out[j] = in[j];
      }
      consume_each (noutput_items);
      std::cout << "\nnFinishing loop in state one" << std::endl;
      return noutput_items;
    }

```

BTW there was a typo in my original email, both state transitions use  
the  
same condition.

Thank you very much for your attention,