Re: [avrdude-dev] support for bitbanging GPIO lines through /sys/class/gpio

[Radoslav Kolev]

On Mon, Apr 12, 2010 at 12:17 AM, Joerg Wunsch <address@hidden> wrote:
> Well, "quite universal" is a quite relative term here.
>
> Did you consider that AVRDUDE runs on (at least) Win32, Linux, MacOS
> X, Solaris and FreeBSD operating systems?  How many of these do
> implement a sysfs gpio interface?

Yes, guilty - it's Linux only. By universal I meant that the sysfs
GPIO interface is independent of the hardware platform and hopefully
in the future every device that has gpio will expose it through sysfs
in this standard way.

> Are there any
> advantages over the existing implementations, in particular in the
> light of most recent PC hardware configurations not offering any IO
> port that could be bit-banged directly (like a classical printer
> port)?

With rare exceptions I don't think regular desktop/laptop computers
will have any GPIO lines exposed. The useful scenario for this feature
is some embedded (x86, ARM, whatever) system running Linux, which
usually have plenty of GPIO lines available.

Quite often, in such a system besides the main CPU running Linux there
can be an AVR handling some realtime tasks for example. The usual way
would be to connect the AVR to the main CPU via a serial link and
update the AVR software using a bootloader. If you don't have a spare
UART on both the main CPU and the AVR or don't have space for a
bootloader on the AVR flash you can just connect it to four spare GPIO
lines and use this to update the firmware.

Besides GPIOs internal to an embedded processor or SoC this could also
work for GPIO expanders on the I2C or SPI bus or anything else that
implements sysfs gpio interface.

> Also, the best way to submit patches is through the patch tracker
> interface.  Patches submitted by email tend to get lost once the
> discussion about them faded away.

OK. I don't insist that this patch be included in the official
avrdude. I just though to share it here in case someone else finds it
useful.

If you say that its worth to consider including it, even though it's
strictly Linux specific, I will add it to the patch tracker.

Regards,
Rado