Why is the pause function not activating?

I don't understand why this code isn't pausing normally. I'll run this section of the script and it'll speed through without pausing, and then I'll type in the same parts of the code piece-by-piece into the command window and pause WILL work.

Short background on the code: I'm controlling two simple servos using Arduino packages.

stepTime = goalTime/(length(invPath(:,1))-1)  % This value is about 0.5
lastq = qStart;

step = 0;
tic
for i=1:length(invPath(:,1)) 
    step = step + 1;

      % Simultaneously Map on Plot
      simMoveRR(.03,lastq,qend,base,L1,L2);  % This plots the results to mock the robot.
      lastq = qend;           

      %Send Command to Arduino; ServoInputVal converts degree input to 0-1 value.
      writePosition(s1, ServoInputVal(rad2deg(invPath(i,1)),s1InputRange,s1ArmRange));
      pause(stepTime/2); % Doesn't work
      writePosition(s2, ServoInputVal(rad2deg(invPath(i,2)),s2InputRange,s2ArmRange)); 
      pause(stepTime/2); % Doesn't work
      toc

      if mod(step,20)==0;  % An attempt to pause the code to review the position. 
          pause             % This doesn't work either.
      end
  end

EDIT: fixed mod input ; still doesn't explain problem with pause. I'm running MATLAB R2016a

Answer 1

[Stephen23]

The reason is because

mod(step,20)

will never output the value 20, and so your comparison

mod(step,20)==20

will never be true. You need to review how the modulo function is defined. Or simply try it yourself:

>> mod(15:25,20)
ans =
    15    16    17    18    19     0     1     2     3     4     5

Do you see any 20's in the output?

To make it work, perhaps either of these will do what you want:

   mod(step,20)==19
   mod(step,20)==0

[Stephen23]

Grant Jones's "Answer" moved here:

Opps, thank you. I didn't see that. BUT it still doesn't explain why the other pause functions aren't pausing. There should be a pause for 1/4 second (stepTime/2) @ line 15 and 17.

[Stephen23]

@Grant Jones: 1/4 of a second is rather quick... I am not sure it would be very noticeable, especially in between writePosition calls which are probably quite slow. Please show what this displays:

disp(stepTime)

[Grant Jones]

Not in a place to run the script at the moment, but stepTime equals 0.5 . I checked this yesterday to be sure.

I agree that it's not that noticeable in a single iteration, but I'm watching the 'toc' output and I'm completing iterations in the FOR loop at about 10Hz which is ~5x too fast.

Thanks for the support so far.

[Jan]

 stepTime = goalTime/(length(invPath(:,1))-1)  % This value is about 0.5

Perhaps this is a wrong assumption? Test this:

disp(stepTime / 2)
tic
pause(stepTime/2); % Doesn't work - sure?
toc

Note: Prefer size(invPath,1) instead of length(invPath(:,1)).

Answer 2

[John BG]

Hi Grant Jones

this is John BG <mailto:[e-mail] [e-mail]>

step is a built in function

Apparently, from the help file it looks like it has to be called with at least 2 arguments, for instance

step(obj,1)

Yet when one keys in just step, MATLAB returns

   step
   Here is an example of how the function step works:
   Consider a randomly generated stable Transfer Function Model:
   of the form G(s)=num(s)/den(s):

num =

           0   -0.1022    0.0316    0.1934   -0.1795    0.1620

.

MATLAB even generates a default damping plot

.

So why don't you try to rename your variable step to something else?

.

if you find this answer useful would you please be so kind to consider marking my answer as Accepted Answer?

To any other reader, if you find this answer useful please consider clicking on the thumbs-up vote link

thanks in advance

John BG

<mailto:[e-mail] [e-mail]>

[Jan]

Shadowing the built-in step function is not the problem here.

Answer 3

[Divyabharathi V]

Try this command before using pause in your code

pause on;

[Stephen23]

+1 Well spotted. Also

pause('query')

to get the current status.

Answer 4

[John BG]

Hi Grant Jones

this is John BG <mailto:[e-mail] [e-mail]>

Again, pause is a MATLAB command, shouldn't you be sending the pause wrapped in a Send-To-Arduino command?

When you say that the pause works, keying in single lines, isn't it that you are pausing the MATLAB application, that in turn pauses the connection to the Arduino, so so it looks as if working, but it isn't really?

When you run the script, the lines containing pause commands, are they really sent to your board?

.

[Walter Roberson]

"shouldn't you be sending the pause wrapped in a Send-To-Arduino command?"

No. It is not the arduino that needs to be paused. Positioning control commands are being sent by MATLAB, and the arduino needs to react to them, and then after a brief time MATLAB needs to send a different command.

It would probably be possible to rewrite portions of the work as an Arduino sketch that received data from MATLAB and executed the appropriate I/O commands, but that is not necessary.