Using the C API?

[hjf]

Could anyone provide me with a small working example of what's discussed here? https://www.kickstarter.com/projects/21 ... sts/679050

Just a simple "Hello World!" function in C that I can call from Python, and the opposite as well.

Thanks!

[dhylands]

Here's a simple sample I put on a github branch:
https://github.com/dhylands/micropython ... 0d64ef7172

Here's the output from running it:

Code: Select all

>>> import c_sample
>>> def foo():
...     print('foo called')
... 
>>> c_sample.set_callback(foo)
>>> c_sample.call_callback()
foo called

And all of the peripherals are essentially similar. Look at things like stmhal/modpyb.c, or stmhal/timer.c (which has an example of calling python from C code).

[hjf]

Thanks a lot!

[hjf]

I tried to base on your code to make a small function but I just can't seem to make it work.

I redefined your C function as:

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STATIC mp_obj_t c_sample_call_callback(void) {
    vstr_t vstr;
    vstr_init_fixed_buf(&vstr, 32, "some_string");

    mp_obj_t obj = mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
    return mp_call_function_1(MP_STATE_PORT(c_sample_callback_obj),obj);

}

and the Python session looks like:

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MicroPython 84405ef-dirty on 2016-02-29; linux version
Use Ctrl-D to exit, Ctrl-E for paste mode
>>> def a(b):
...     print(b)
...
...
...
>>> import c_sample
>>> c_sample.set_callback(a)
>>> c_sample.call_callback
<function>

What am I doing wrong?

[dhylands]

You're missing the parenthesis when you're trying to call the call_callback function. Instead of

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>>> c_sample.call_callback

you should be using

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>>> c_sample.call_callback()

[hjf]

You're missing the parenthesis when you're trying to call the call_callback function

Ah yes. Also known as the "don't try to program when it's 1AM and your eyes can't even focus on the screen"

But now I get this:

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>>> c_sample.call_callback()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
MemoryError: memory allocation failed, allocating 1 bytes

[dhylands]

You're misuing vstr. In particular, the vstr passed into mp_obj_new_str_from_vstr needs to be heap allocated.

You could use:

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STATIC mp_obj_t c_sample_call_callback(void) {
    mp_obj_t obj = mp_obj_new_str("some_string", strlen("some_string"), false);
    return mp_call_function_1(MP_STATE_PORT(c_sample_callback_obj), obj);
}

You'll need to also add a #include <string.h>. This produces:

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>>> def foo(b):
...     print(b)
... 
>>> import c_sample
>>> c_sample.set_callback(foo)
>>> c_sample.call_callback()
some_string
>>> 

If you wanted ot use a vstr, you'd need to do something like:

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STATIC mp_obj_t c_sample_call_callback(void) {
    vstr_t vstr;
    vstr_init_len(&vstr, strlen("some_string"));
    strcpy(vstr.buf, "some_string");
    mp_obj_t obj = mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
    return mp_call_function_1(MP_STATE_PORT(c_sample_callback_obj), obj);
} 

which produces:

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>>> def foo(b):
...     print(b)
... 
>>> import c_sample
>>> c_sample.set_callback(b)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'b' is not defined
>>> c_sample.set_callback(foo)
>>> c_sample.call_callback()
b'some_string'

mp_obj_t obj = mp_obj_new_str("some_string", strlen("some_string"), false);

[cduran]

Could I add more C callbacks without modifying mpconfigport.h?

[dhylands]

Could I add more C callbacks without modifying mpconfigport.h?

You only need to modify mpconfigport.h to add the module. Once the module has been added you can add as many methods to the module that you want by just modifying c_sample.c (or whatever you call your module).

By convention, I probably should have called the source modsample.c.

[cduran]

Could I add more C callbacks without modifying mpconfigport.h?

You only need to modify mpconfigport.h to add the module. Once the module has been added you can add as many methods to the module that you want by just modifying c_sample.c (or whatever you call your module).

By convention, I probably should have called the source modsample.c.

Wouldn't I also have to add the new callbacks to qstrdefsport.h?