Date: Sat, 11 Apr 2015 18:00:46 -0700 From: Rui Paulo <rpaulo@me.com> To: freebsd-arch@freebsd.org Cc: Adrian Chadd <adrian@freebsd.org>, "freebsd-embedded@freebsd.org" <embedded@freebsd.org> Subject: Re: using libgpio to bitbang LCDs! Message-ID: <7527478.9HOi23WthO@akita> In-Reply-To: <CAJ-Vmo=n=Lfh_XqkxwAA43jUi7suoPjWV1uSv4VnKNncw3%2BPfw@mail.gmail.com> References: <CAJ-Vmo=n=Lfh_XqkxwAA43jUi7suoPjWV1uSv4VnKNncw3%2BPfw@mail.gmail.com>
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On Saturday 11 April 2015 17:11:47 Adrian Chadd wrote: > Hi! > > I just ported an adafruit LCD driver to FreeBSD. This was a pretty trivial > task: > > * convert C++ to C, which was done primarily to not rely on the > arduino-isms; * use libgpio to bitbang the SPI bus needed to write to the > LCD. > > It worked third time. First was "oh it runs on 5v power and 3.3v > signaling", and I had it hooked up to 3.3. Second was "Oh, I haven't > set the pins to be output pins yet." Third time worked - just slowly. > > However - using libgpio was just pleasant. Get a handle, set the pin > config, set the pins high/low. It was pretty damned wonderful. > > It turns out that to fill the screen with individual pixel writes > takes quite a few seconds pinning my AR9331 CPU doing ~ 190,000 > syscalls a second. Ian's suggested something sensible - a bulk data > ioctl() that can bit bang a series of GPIO pins in the kernel. Ie, one > syscall, a big chunk of data with instructions and timings. Since this is an LCD, you probably want a way to export the GPIO bank via mmap with write-combining enabled. It's not really a safe operation as it could hang the GPIO driver, but it could be useful. > The other interesting thing would be a kind of bulk pin set/get - ie, > instead of doing rmw for one pin at a time, communicate down masks of > pins to do together. I think that's sensible and could be done via a separate (new) ioctl. -- Rui Paulo
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