On Mon, Dec 1, 2014 at 4:59 AM, Dan Egli <[email protected]> wrote:
> I was thinking of various uses one could put a Raspberry Pi to, and a
> question occurred to me. I know the Model B (and B+) have an Ethernet port
> built in. Has anyone ever seen a shield, or other method (besides USB) of
> including an additional port on the Pi? I know that the GPIO pins will
> allow you to do a lot via shields and/or expansion boards connected via
> ribbon cable, but I don't know if there's a good way of linking the GPIO
> pins to the pins to the pins of an Ethernet controller (or Fast Ethernet or
> whatever). Does anyone know of such a device? If so, does it work with the
> standard Raspbian distro? I know there are "Ethernet shields" for Arduino,
> but then I'd have to write a heck of a lot more code to do the same thing
> as I can accomplish with Raspbian on the Pi and a board that provides an
> extra Ethernet port. Not to mention how much slower an Arduino is compared
> to the CPU on the RPi.
What are you intending to do with an extra Ethernet port on a RPi?
IIRC, the onboard Ethernet is connected via USB in the first place,
which is a bit unfortunate because the RPi USB support is not great
due to poor USB hardware that requires a lot of stuff that's normally
implemented in hardware to be implemented in the driver instead. This
makes the Ethernet not-particularly-fast and putting a bunch of
data-heavy peripherals on the USB bus can lead to issues. In fact,
most of the hardware on the RPi is pretty lame, except for the video
core. If you look at a "map" of the die, the vast majority of the
real-estate is dedicated to the video system, a tiny square is devoted
to the old ARM core, and the other peripherals are pretty much
invisible. This is NOT the SoC you're looking for if you want to do
anything that requires horsepower besides whatever codecs they supply
for the video core. I mean, it's a lot faster CPU-wise than a typical
Arduino, but that's not saying much.
This makes RPi a really poor candidate for a router, so I'd start
looking elsewhere if that's what you were planning. And for most other
multi-port Ethernet uses, it's probably cheaper and better to hook
your RPi up to a switch instead of trying to add more Ethernet ports
to it.
As to Arduino Ethernet shields, they're really Ethernet+TCP/IP
Shields. They present a serial interface to the Arduino along with a
command set that you use to program the TCP/IP parameters you want to
use. The chip on the shield is basically another microcontroller that
handles all the network protocols, so it's very much *not* a regular
Ethernet interface and wouldn't show up as "eth1" or whatever on your
RPi if you got them physically interfaced. Again, this is not going to
be a very high-performance interface.
--Levi
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