Developing your first pyb module:

[SwimDude0614]

Hello all. I am going to document, as best I can, creating my first hardware pyb module. The end-result will be a CAN bus since there is currently no implementation in pyb and I would like to use it.

I make *NO* promises as to the usefulness or accuracy of any information given below. As I type this now, I have only just started creating my first module, so what you will read are not the words of an experienced micropython developer but simply someone thinking out loud as he stumbles his way through it.

I am relying on the more experienced members here to correct me where I go wrong and hopefully add some helpful tips along the way.

The work can be found on the wiki here: http://wiki.micropython.org/Creating-Pyb-Modules
and I hope we can get some good discussion and questions going on here. I know I'll have lots of ???s along the way!

[dhylands]

Hello all. I am going to document, as best I can, creating my first hardware pyb module. The end-result will be a CAN bus since there is currently no implementation in pyb and I would like to use it.

When I'm all done, I will try and compile this into a useful and indexed PDF (or another format? who knows). We'll see how much motivation I have left by the end of it.

I'd recommend creating a Wiki page. This can then be edited/updated by others.
http://wiki.micropython.org/Home

[SwimDude0614]

Oh wow... now I feel truly stupid. To the wiki I go...

[SwimDude0614]

Can a moderator/admin delete all the reserved posts? I'd like to keep the thread around for questions/discussion though

[dhylands]

Can a moderator/admin delete all the reserved posts? I'd like to keep the thread around for questions/discussion though

Done

[SwimDude0614]

Here we go with the questions!

What is the first member of _mp_obj_type_t? It reads:

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struct _mp_obj_type_t {
    mp_obj_base_t base;
   ....
   ...
};

Poking through the definitions and its usage makes it look like recursive definitions? I'm certainly confused what is happening and why.

[dhylands]

Here we go with the questions!

What is the first member of _mp_obj_type_t? It reads:

Code: Select all

struct _mp_obj_type_t {
    mp_obj_base_t base;
   ....
   ...
};

Poking through the definitions and its usage makes it look like recursive definitions? I'm certainly confused what is happening and why.

Every object in python has a type. base describes that type. A type itself will often have base set to mp_type_type which corresponds to the python type 'type'.

For example: https://github.com/micropython/micropyt ... /led.c#L53 this declares an instance of the pyb_led_type. The pyb_led_type itself: https://github.com/micropython/micropyt ... led.c#L292 is a type, and its an instance of mp_type_type.

In python:

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>>> led = pyb.LED(1)
>>> type(led)
<class 'LED'>
>>> type(type(led))
<class 'type'>
>>> type(pyb.LED)
<class 'type'>

[dhylands]

Looking at the example you posted on your wiki page, you've got:

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const mp_obj_type_t pyb_saab_type = { {&mp_type_type } };

Now lets suppose that you want to have a statically declared object of the type pyb_saab_type. Since you didn't post your type, I'll make one up, that just stores the year of the saab.

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typedef struct {
    mp_obj_base_t base;
    machine_uint_t year;
} pyb_saab_obj_t;

Now you could go ahead and declare some static instances of this like so:

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const pyb_saab_obj_t first_car  = {
    { &pyb_saab_type },
    1997
};

Now, let's create a print function for your saab object:

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void saab_obj_print(void (*print)(void *env, const char *fmt, ...), void *env, mp_obj_t self_in, mp_print_kind_t kind) {
    pyb_saab_obj_t *self = self_in;
    print(env, "<SAAB year %lu>", self->year);
}

And a function to dynamically allocate some new ones:

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STATIC mp_obj_t saab_obj_make_new(mp_obj_t type_in, uint n_args, uint n_kw, const mp_obj_t *args) {
    mp_arg_check_num(n_args, n_kw, 1, 1, false);
    // get year
    machine_uint_t year = mp_obj_get_int(args[0]);

    pyb_saab_obj_t *self = m_new_obj(pyb_saab_obj_t);
    self->base.type = type_in;
    self->year = year;

    return o;
}

and lets create a function to return that statically allocated object:

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STATIC mp_obj_t saab_first_car(void) {
    return (mp_obj_t)&first_car;
}

I'll leave the rest (tying this all together) to you for now.

[SwimDude0614]

That stuff is gold, thank you! Most of that I've done and was going to type up tonight, but the dynamically allocated object was something I hadn't yet figured out (and really wanted).

[SwimDude0614]

Didn't get much further tonight, but I did improve on the format a lot and added a bit of content. Should be much easier to read going forward. Work will be very minimal for the next several days. I have plans this weekend and preparations to make (Anyone here familiar with TSD rally?! )