two questions: why USB2 instead of USB3 and will there be a multi-nic version at some point?

Hi Pete

Thanks for the reply. I've got absolutely no problem with the hardware decisions you've made, especially considering you're primarily catering for the educational market! I'm sure as costs come down and you start getting more feedback from users you'll probably add new functionality into the next generation of RPi, however for the time being, I think you guys have done a fantastic job.

I'm also looking forward to seeing the latest demo of RISC OS running on an RPi in Wakefield next month, now that would definitely rekindle some fond memories - I just hope I can ressurect my 120MB harddrive from my old Acorn A3010 and retrieve my first few years worth of programming!

One of the design targets for USB 1 was that "standard" chips could drive it. That's why you see software implementations of USB on Atmel ATMEGA8 chips and things like that. The lowest level hardware interface would work at 12Mbps, but then the software wouldn't be able to keep up. But if you design a chip USB1.1 is easy on the hardware level. (the protocols are kind of complicated).

Next there is USB2.0, the "high speed, 480mpbs" variant. This requires slightly special drivers, lower voltages for the core electronics, but with modern processors running 500MHz+ this isn't much of a problem. This is what the broadcom has.

Now upgrading from there to USB3.0 means that the stuff is much more difficult to integrate in an existing chip design. Many chips are either specific USB3.0 chips, or they need a special driver chip. In short not something that is easily bolted onto the broadcom chip that powers the 'rpi.

USB2 is built right into the CPU - USB3 would require additional hardware, and the Raspberry Pi probably couldn't move data fast enough to saturate USB2 anyway.  I think I heard it has something like 60MB/s of bandwidth for ALL the IO, including USB.

I doubt there will ever be a multi NIC version, but there really doesn't need to be when USB hubs and ethernet adaptors are avaliable for $3.99.

I am not sure of the need for a multi nic version. If you want a cheap multi nic system running linux you could just get a cheap router and flash open-wrt on it

You don't need 2 NIC for that. Set it up as as a gateway in a network and teach the kid to play with iptables but I'm not sure linux firewall even works with ARM.

I would also point out that not all USB 3.0 chipsets play "nice" with Linux yet.

I have had bad experiences with the Fresco Logic 1000 series for example.

Probably better to stick with well tried technology at this point.

Thanks for all the info.  I didn't realize that USB3 was so cumbersome to implement.  As to the thoughts on multiple nics, I understand the desire for cheap hardware and to keep the size down, but I don't understand the comments about multi port hubs and cheap ethernet adaptors.  Having a multiport ethernet hub solves nothing when that hub is connected to a single nic since hubs, by design, are dumb and don't understand routing rules (and if you mean a multiport USB hub, I don't know how you would use that as a multinic ethernet device at all).  All traffic on every port of an ethernet hub (and I'm speaking strictly of multiport hubs, not multiport routers/switches) is seen by every other port on that hub and so it's impossible to run multiple ethernet networks on a hub (and defeats the purpose of my thought of having one nice little inexpensive card as a firewall device; adding extra hardware now increases the cost to the point where you might as well pick up, as another poster pointed out, a cheap router flashed with open-wrt or tomato and forgo the PI completely).  You *could*, as another poster mentioned, purchase a USB nic and have two nics that way, which is a possibility but then one of the USB ports is now used as a dedicated port for routing (not an issue if you have a USB hub to connect keyboard and mouse to the other USB port).  Anyway, this discussion has been very informative for me and I appreciate all of the comments.

No, I did mean a USB2.0 hub and USB2.0 ethernet adaptor.  Both are common and cheap.

This is actually how the Model B works internally.  The system-on-a-chip provides one USB2.0 port.  A USB2.0 hub and ethernet adaptor are soldered on to the board.  USB2 is the fastest bus provided by the chip, AFAIK.

All add-on devices have to be USB and share that single 480Mbps half-duplex connection.  That means you have just barely enough bandwidth to max out two full-duplex 10/100 ethernet adaptors.  If you have fast large storage on your USB as well, that would be a point of congestion (but only if all traffic, including hard drive activity, is heavily bidirectional)

Hey Pete,

Thanks for clearing that up, now I personally understand why you did what you did to cut down on the price. Are there any future plans though to create a more full-featured version of the RPi? For those kids who have learned the basics with the RPi, would there then be a more advanced version for the next step for them, and for the community that wants to use them and develop them more than they could with the RPi that is currently out? This would then challenge the kids farther and also stimulate the communities minds about possible developments to the RPi.

Anthony Brown wrote:

 

I am not sure of the need for a multi nic version. If you want a cheap multi nic system running linux you could just get a cheap router and flash open-wrt on it

Yeah. But I pay about $60 for a cheap open-wrt-capable router. And only $35 for the RPi. And with  a router you end up with: Is this thing actually the same as the one that Openwrt runs on?

Anyway, for some time to come, RPi will, with an extra USB-ethernet interface be fast enough to saturate the WAN connection  for most people.