[En-Nut-Discussion] Unified GPIO implementation

[Thiago A. Corrêa]

Hi,


    I've just created a branch ugpio (unified gpio) to commit changes
related to the Wiki specs.
    Already added the mandatory and optional constants with some
sensible defaults to include/dev/gpio.h
    Having defaults in gpio.h also lets us keep the Doxygen tags in
just one file.

Kind Regards,
   Thiago A. Correa


On Wed, Oct 20, 2010 at 6:23 AM,  <uprinz2 at netscape.net> wrote:
> Hi!
>
>
> I fully agree. STM32 does support PullDown too for inputs.
>
>
> I'll check the wiki and update it.
>
>
> Best regards
> Ulrich
>
>
> -----Original Message-----
> From: Thiago A. Corrêa <thiago.correa at gmail.com>
> To: Ethernut User Chat (English) <en-nut-discussion at egnite.de>
> Sent: Wed, Oct 20, 2010 4:46 am
> Subject: Re: [En-Nut-Discussion] Unified GPIO implementation
>
>
> Hi All,
>
> About the wiki article, in the part it says:
>
> The obsolete definitions:
>
> #define GPIO_CFG_MULTIDRIVE  Enable Open-Drain: This should default as
> PushPull can break the chip if enabled by accident.
>
> It is dangerous to have PushPull as default with GPIO_CFG_OUTPUT. If
> one uses the examples with a slightly different board it might kill
> the hardware. So default should be Open-Drain or Weak Pullup if the
> CPU supports that. If PushPull is supported it must be set by reason
> and under programmers control.
>
> ---
>
> Actually, I think the PushPull is the one that is not available on
> most platforms. AVR32 and AVR 8 bits both have weak pull ups refered
> as simply pull up, and in the case of AVR32 there is a open-drain
> enable register.
>
> I think we should then have a definition where PushPull must always be
> explicitly enabled, never default. And output should be open-drain if
> the CPU supports that. Therefore remove the "Weak pullup" case from
> the specification, as it's simply GPIO_CFG_PULLUP and it's dealt with
> as a flag of it's own if the user wants it enabled.
>
> Based on that, I'm making the changes as this:
>
>    if (flags & GPIO_CFG_OUTPUT) {
>        gpio_port->oders = mask;
>        /* Unless specified, outputs default open-drain in Nut/OS */
>        if(flags & ~GPIO_CFG_PULLUP)
>            gpio_port->odmers = mask;
>        else
>            gpio_port->odmerc = mask;
>    } else {
>        gpio_port->oderc = mask;
>    }
>
> ODMER is the register to enable Open Drain mode in AVR32.
>
> Also, if you assume that PushPull is the special case, than this part
> should also be modified:
>
> #define GPIO_CFG_PUSHPULL    AVR: Enable Pullup, ARM/Cortex: Enable
> strong pull-up.
> #define GPIO_CFG_PULLUP      Enable Pullup.
>
>
> to
>
> #define GPIO_CFG_PULLUP        Enable (weak) Pullup, (AVR, AVR32, ARM/Cortex).
> #define GPIO_CFG_PUSHPULL    Enable strong pull-up if available (ex.
> ARM/Cortex), otherwise it's just #define GPIO_CFG_PUSHPULL
> GPIO_CFG_PULLUP
>
> One other thing, we might need an GPIO_CFG_PULLDOWN as well. Looks
> like there are AVR32 parts with this feature judging from the Atmel
> Software Framework source code in the repository.
>
> Kind Regards,
>     Thiago A. Correa
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