[En-Nut-Discussion] Unified GPIO implementation

[Thiago A. Corrêa]

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