Is there an easy way to pass machine object (e.g. PWM) of a port into user C module?

[by1e11]

Hi, we are trying to develop an external C module on esp32, starting from the cppexample user module example. We successfully built the the custom firmware, things are all good until we started to use the hardware PWM peripheral. What we expected to implement is to initialize a PWM from python and pass the pwm object to a C function to use in the C module. I searched a lot, but found few information about this topic. Any suggestion or guidance is appreciated. Thanks

[shariltumin]

To pass a pwm object from Python to C, you basically do this:

machine_pwm_obj_t *self = MP_OBJ_TO_PTR(args[0]);

The file ports/esp32/machine_pwm.c is where the machine_pwm_obj_t is defined for a specific port (here esp32).

The file micropython/extmod/machine_pwm.c defines the methods to be used in MicroPython.

for example,

// PWM.freq([value])
static mp_obj_t machine_pwm_freq(size_t n_args, const mp_obj_t *args) {
    machine_pwm_obj_t *self = MP_OBJ_TO_PTR(args[0]);
    if (n_args == 1) {
        // Get frequency.
        return mp_machine_pwm_freq_get(self);
    } else {
        // Set the frequency.
        mp_int_t freq = mp_obj_get_int(args[1]);
        mp_machine_pwm_freq_set(self, freq);
        return mp_const_none;
    }
}
static MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(machine_pwm_freq_obj, 1, 2, machine_p
wm_freq); 

This is what get called when you do:

freq = pwm.freq()

[by1e11]

Hi @shariltumin, thanks for the reply, that's exactly what I expected to implement. Then the question is how could I include and link the functions in micropython/extmod/machine_pwm.c, say allowing me to call for example self->mp_machine_pwm_freq_set() from my C function. I noticed there is no public header exposed for machine_pwm.c, I tried to make my own to expose some needed functions, but failed in the linking step. I guess I should make some modifications on the make files?

[shariltumin]

I wrote a short tutorial that might be helpful. You can find it at https://github.com/shariltumin/c-module-tutorial-micropython

[by1e11]

That's a great tutorial, I'll give it a try. Thanks