[Microbit-Python] Pulsing I/O pins

[Nigel Kendrick]

Agreed on both counts (timing and bytecode) - just keeping things simple!

On 10 June 2016 at 12:47, Radomir Dopieralski <microbit at sheep.art.pl> wrote:

> I'm not sure this is a good way to time things. It may change
> arbitrarily with updates or even depending on the version of compiler
> you use to compile the micropython code...
>
> Comments will not have any effect, because Micropython is not, in fact,
> an "interpreted" language in the sense that BASIC was. It is compiled
> into bytecode, that is then executed on a virtual machine. Comments get
> removed in the compilation step.
>
> On Fri, 10 Jun 2016 12:37:36 +0100
> Nigel Kendrick <nigel.kendrick at gmail.com> wrote:
>
> > Hi folks,
> >
> > I had to take some timing measurements so I thought I'd share just in
> > case it's of use:
> >
> > For those without access to a 'scope (or who can't be bothered to
> > drag it out!), if you toggle an I/O pin by writing something like
> > this in the Block Editor:
> >
> > digital write 0 to pin P2
> > digital write 1 to pin P2
> > digital write 0 to pin P2
> >
> > You get a pulse with a 5uS duration.
> >
> > Adding extra 'high' stages adds 5uS per stage - example:
> >
> > digital write 0 to pin P2
> > digital write 1 to pin P2
> > digital write 1 to pin P2
> > digital write 0 to pin P2
> >
> > Gives a 10uS pulse and so on.
> >
> > Repeating the same experiment in micropython, things are slower
> > because the language is interpreted:
> >
> > from microbit import *
> >
> > pin2.write_digital(0)
> >
> > while True:
> >     pin2.write_digital(1)
> >     pin2.write_digital(0)
> >     sleep(1)
> > # End of while loop
>
> https://bitbucket.org/thesheep/micropython-ili9341/src/4fe3cd28006e171eec16aff9e7cbae8ed394f88d/ili9341.py?fileviewer=file-view-default#ili9341.py-142:157
> >
> > 1 x pin2.write_digital(1) = 68uS
> >
> > 2 x pin2.write_digital(1) = 136uS
> >
> > etc.
> >
> > You could stretch the timing using loops - and above 1mS you could
> > pause/sleep - but just repeating the pin writes seems more controlled
> > and easier to work out.
> >
> > I tried padding the highs with comments - eg:
> >
> > while True:
> >     pin2.write_digital(1)
> >     #
> >     #
> >     pin2.write_digital(0)
> >     sleep(1)
> > # End of while loop
> >
> > but the difference, if anything, was negligible.
> >
> > -- Nigel
>
>
>
> --
> Radomir Dopieralski
>
> --
> Radomir Dopieralski
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