[ell-i-developers] Re: PWM working for TIM2

  • From: Pekka Nikander <pekka.nikander@xxxxxx>
  • To: ell-i-developers@xxxxxxxxxxxxx
  • Date: Wed, 29 Jan 2014 22:04:17 +0200

>>> To really make the PWM work, still the GPIO alternate functions need to be 
>>> initialized, do I work on that in parallel with the Serial testing?
>> 
>> Please remind me what this was about?
>> 
> Is the setting of the alternate functions:
> 
> https://github.com/Ell-i/Arduino/blob/ell-i/hardware/ell-i/stm32/variants/ellduino_stm32f051/stm32f051_init.c#L321
> 
> Serial sets them in begin routine, but there is not initialization part for 
> analogWrite. The timer is activated, but it can't access the pins.

I see.  I have completely forgotten that we need to not only activate the GPIO 
peripherals in the RCC register, but also to initialise them for analogWrite, 
SPI, and perhaps other functions.  I thought about that back in November but 
alas my memory is too short.  (Or there are too many things I'm trying to 
remember. :-)

Anyway, we have here a small architectural problem.  Architecturally, each GPIO 
pin is a separate entity, and has a separate mode, output type, output speed, 
pull up/down, and alternate function setting.  However, if we just simply 
declare them separately for each pin, we consume quite a lot of memory as we 
would have to define about 6 * 32 bits for each pin.  On the other hand, if we 
define each GPIO register initialisation value, as we've done in the old 
runtime, then the definitions for each pin get dispersed over several lines in 
the source code, which is bad from the modularity and maintenance point of view.

That is, I'd like to use a macro like

DEFINE_GPIO_PIN_INIT(B, 2, INPUT, ..., AF2);

One line for each pin.  

The simple approach would then to generate a simple init record like
   const SystemInitRecordArrayData32NoAddress ... {
        ...
 D32(GPIO_TypeDef, AF[0], GPIO_AFRx_AFRx3_AF2)

However, that would consume excessive memory, as I wrote.

Perhaps we could generate static const values out of the macro, and then 
combine them?  Something like

  ...
  static const __GPIOB_PIN2_AF = GPIO_AFRx_AFRx3_AF2;
  ...
  const SystemInitRecordArrayData32NoAddress ... {
        ...
         D32(GPIO_TypeDef, AF[0],
                __GPIOB_PIN0_AF |
                __GPIOB_PIN1_AF | 
                ...

What do you think?  Would that work?  Could you perhaps try it, Ivan?  Or 
should I?

--Pekka


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