Date: Mon, 2 Mar 2015 20:30:58 +0100 From: Milan Obuch <freebsd-arm@dino.sk> To: Luiz Otavio O Souza <lists.br@gmail.com> Cc: freebsd-arm@freebsd.org Subject: Re: Raspberry Pi with PiTFT - some GPIO weirdness Message-ID: <20150302203058.0d44266b@zeta.dino.sk> In-Reply-To: <CAB=2f8wv9X%2B-=AwBf-_6-Pzc49icWU7KV%2BU0t_qr=uX45BjbXw@mail.gmail.com> References: <20150228111852.15affe31@zeta.dino.sk> <20150228193658.6c872779@B85M-HD3-0.alogt.com> <20150228142424.6fed0ecf@zeta.dino.sk> <CAB=2f8wv9X%2B-=AwBf-_6-Pzc49icWU7KV%2BU0t_qr=uX45BjbXw@mail.gmail.com>
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On Sat, 28 Feb 2015 15:43:30 -0300
Luiz Otavio O Souza <lists.br@gmail.com> wrote:
> On 28 February 2015 at 10:24, Milan Obuch wrote:
> > On Sat, 28 Feb 2015 19:36:58 +0800
> > Erich Dollansky wrote:
> >
> >> Hi,
> >>
> >> On Sat, 28 Feb 2015 11:18:52 +0100
> >> Milan Obuch <freebsd-arm@dino.sk> wrote:
> >>
> >> > today I found some time to play a bit with my little display
> >> > attached to Rasoberry Pi, and I decided to test buttons connected
> >> > to GPIO, as this should work on FreeBSD already. According docs,
> >> > buttons are connected to GPIO lines 23, 22, 21 and 18, leftmost
> >> > first.
> >> >
> >> > Using basic 'gpioctl -f /dev/gpioc0 -lv' command I found only
> >> > first one, on line 23, reacts. It has value 1 normally and 0
> >> > when pressed.
> >> >
> >> you must setup the pins as inputs first before using them as
> >> inputs. I would not rely on any defaults.
> >>
> >> Erich
> >
> > According available docs, all GPIO are set to input mode after
> > reset. This seems not to be the case, but that's not my point. What
> > was a bit of surprise for me was even 'gpioctl -f /dev/gpioc0 -l'
> > tells those pins are in input mode ('pin nn<IN>'), it did not work.
> > And fact that even after power disconnect the state remains the
> > same is even more weird.
> >
> > Anyway, I accept the necessity for setup, the question is, where
> > should these setup instruction go.
> >
> > Regards,
> > Milan
>
> The GPIO driver do not touch the pin settings at boot, there are a few
> things like the LAN reset (GPIO pin 6) where we hope the loader is
> doing the right thing.
>
> Only a few drivers are checking and making sure that the pins they use
> have the right settings at boot.
>
> What I see from PiTFT schematics is that the push buttons doesn't have
> any pull-ups resistors, so it must rely on RPi settings.
>
> Please try the following (set the pin as input with pull-up enabled):
>
> gpioctl -c 18 in pu
> gpioctl -c 21 in pu # or 27 for rev. 2
> gpioctl -c 22 in pu
> gpioctl -c 23 in pu
>
> HTH,
> Luiz
So, with some experimenting I can confirm this works. And after looking
a bit more into available docs I understand it better - even the
behavior which surprised me a bit.
In BCM2835 ARM peripherals, page 100, GPIO pull-up/down register,
second paragraph, second sentence: GPIO pull-ups are maintained even in
power down mode when the core is off.
So nothing unclear anymore, it just takes a bit of time to find all
relevant information bits.
Regards,
Milan
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