[Microbit-Python] error code?... :(020

Mon Sep 28 01:30:56 CEST 2015

That looks nice!

From: ben at raspberrypi.org
Date: Fri, 25 Sep 2015 21:43:58 +0100
To: microbit at python.org
Subject: Re: [Microbit-Python] error code?... :(020

If anyone's interested, we just added a nifty callback feature into gpiozero (the kid friendly GPIO lib for Raspberry Pi I'm working on).

Example usage:

button = Button(2)  # gpio pin 2
led = LED(3)  # gpio pin 3

button.when_pressed = led.on
button.when_released = led.off

See the code here: https://github.com/RPi-Distro/python-gpiozero/blob/master/gpiozero/input_devices.py

All credit to the genius that is Dave Jones.
Ben

---

Ben Nuttall
Education Developer Advocate
Raspberry Pi Foundation
www.raspberrypi.org

UK registered charity 1129409

On 25 September 2015 at 14:50, Damien George <damien.p.george at gmail.com> wrote:
Regarding the event queue.  This is something that's implemented in

the underlying DAL, it's nothing to do with MicroPython.

There is a message bus and events can be posted to the message bus,

with a timestamp.  You can attach arbitrary C/C++ functions to be

called when an event is posted.

For example, with the buttons, when the button state changes then

events are generated.  The buttons have software debouncing and also

timing to see how long they have been pressed.  The events are:

- button high transition

- button low transition

- button click

- button long press

- button held

Events will remain on the queue until the handler is run.  Since the

threading scheme of the DAL is cooperative your code must yield for

the events to be processed.  This is likely to change very soon so

that events handlers are executed preemptively (on an interrupt).

Currently in the MicroPython bindings to the DAL we don't use these

events.  We simply return the current state of the button (high or

low) as read on the button GPIO.

But probably it's a good idea to use these events so that you can

react to a "click" without sitting in a tight polling loop.

The difficult thing will be to make a clean API that doesn't require

the user to know/understand events or preemption, and doesn't require

them to yield or make sure the queue doesn't overflow.

We could try something like:

button.is_held() # simply get the state of the GPIO as it currently does

button.was_clicked() # return true if the button was clicked since the

last call to this function; resets the state to false

button.was_long_clicked() # same as above, but for long click

We anyway need a similar set of concepts for gestures (eg

gesture.did_fall(), gesture.was_shaken()).

Thoughts?

On Fri, Sep 25, 2015 at 2:09 AM, Alan <alainjackson at hotmail.com> wrote:

>

> I've just been writing myself an event queue for button pushes etc... maybe

> that's not necessary if there already is one, if it's accessible.

>

> Cheers,

>

> Alan

> ________________________________

> To: microbit at python.org

> From: larry at hastings.org

> Date: Thu, 24 Sep 2015 14:17:17 +0100

> Subject: Re: [Microbit-Python] error code?... :(020

>

>

>

> I wish to understand this more.  Micropython has an internal,

> hidden-from-view, event queue?  How do I examine and interact with it?

>

> I thought button_a.is_pressed() was polling; is it watching for button

> events on this event queue?  Does that imply that I can get delayed /

> buffered button presses?

>

> In general how do I keep the event queue from filling?

>

>

> /arry

>

> On 09/23/2015 01:54 PM, Damien George wrote:

>

> Hi Alan,

>

> Error code 020 is "out of memory".

>

> The problem is as you guessed: there is an event put on the event

> queue each time the button is pressed.  To clear this queue your code

> needs to "yield".  You can do this by putting sleep(1) in your loop.

>

> This is totally unexpected behaviour and I'll work out how to fix it

> (Ie your code should just work).

>

> Cheers,

> Damien.

>

>

>

> On Wed, Sep 23, 2015 at 4:02 AM, Alan <alainjackson at hotmail.com> wrote:

>

> Error code update.

>

> I'm consistently getting the ":( 020" code after 42 button presses (of any

> combination of buttons A and B).

>

> Is there a button click buffer that's overflowing somewhere? If there is I

> can't see a method on the microbit API to clear it.

>

> Cheers,

>

> Alan

>

> ________________________________

> From: alainjackson at hotmail.com

> To: microbit at python.org

> Date: Wed, 23 Sep 2015 00:28:51 +0000

> Subject: [Microbit-Python] error code?... :(020

>

>

> Hi,

>

> I wrote a small program to draw on the LED matrix, but after setting a few

> LEDs on I get what looks like an error message on the LEDs:

>

> ":(020"

>

> (Frowny-face zero two zero)

>

> It just keeps repeating that and my program stops but there's no stack trace

> on the python repl.

>

> Is that a built in hardware error code or something? Has anyone else seen

> that?

>

> Here's my program:

>

> ====8<====

>

> from microbit import *

>

> index = 0

>

> while True:

>     if button_a.is_pressed():

>         x = index % 5

>         y = int(index / 5)

>         display.image.set_pixel_value(x,y,

> not(display.image.get_pixel_value(x,y)))

>

>     if button_b.is_pressed():

>         index = (index + 1) % 25

>

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