Can micro:bit read while in another while?

Question

so i have got a problem programming micro:bit. I code it in internet page, then download the hex file and transfer it into the micro:bit. On the internet simulator everything works. Apparently when i transfer it to micro:bit code is not working. The code is really simple, it looks something like this.

animation repeats while variable is 0 (this part works perfectly)
A button makes the variable 1, B makes it 2 (this part works)
when variable is not 0, it breaks first animation loop. (this part also works)
then goes to second loop which repeats while variable is NOT 0 (it will never be a 0 because there is no button which makes variable 0) so it repeats for ever (this works)
in second loop, there are 2 more loops. First repeats when the variable is 1, second when the variable is 2. That makes me able to switch between these 2 loops any time i want. (Problem appears here: i am in loop 2 for example, i cant switch to first loop and otherwise.)

All these errors occurs in micro:bit robot, when code is transferred. In internet simulator code works perfectly. Is it possible to do that code in micro:bit, have i reached limit? Or is robot defective? Thanks for answers and inform me if something is not clear.

Matthew Frost · Accepted Answer · 2017-10-17T19:43:38.567

This is of course very hard to debug without seeing any blocks/code as I don't know how you are detecting the buttons being pressed when in the second loop.

However, this may be a scheduling issue due to the way you are changing the variable upon a button being pressed. Perhaps consider restructuring your blocks such that they are more event driven, utilising blocks such as on button A Pressed a bit better, infinite while loops are always best to avoid. Also, maybe consider putting a pause(100) in the while loops.

Hope this helps ;)

Edit:

OP confirmed that the pause(100) worked (see comments of this answer), demonstrating that it was a scheduling problem!

For those who are interested ;)...this is because the CPU is busy executing the while loop and doesn't have time to think about the buttons being pressed. The pause(100) allows the CPU to rest for a bit and not think about the while loop, giving it the time needed to deal with the button press. This is known as Cooperative Scheduling!

You can find out more about Cooperative Scheduling at:

https://www.microbit.co.uk/device/reactive

I added pause(100) in every loop and everything works great. Thanks for solution. — Augustas Mirinas, Oct 13 '17 at 17:16
No problem, glad I could help. See the edit I have made as to why this was happening. — Matthew Frost, Oct 17 '17 at 19:45

score -1 · Answer 2 · answered Oct 10 '17 at 12:49

If your code looks like this, you will never be able to change your state variable. You'll get stuck in one of the inner loops, with no option to change the control variable.:

while (unset):
  Animate
  Check for button
While (set): // Intend to be stuck in this loop forever
  While (one):
    Do first
  While (two):
    Do Second

What you need is to be able to update your state:

...
  While (one):
    Do First
    if (button_b.was_pressed()):
      state = two
...

This still isn't perfect, you might want to think about what happens if the buttons are pressed in 'unusual' sequences. The simulator should be identical, but there might be something unusual about the way that button presses are handled and your code that have broken the simulator. If the simulator really is broken, you'll need to share a testcase with the micro:bit team.

Can micro:bit read while in another while?

2 Answers2