A or B


6 posts
by Lactobacillus » Thu Apr 26, 2012 11:35 am
As far as I know the Ethernet and the USB in model B is connected via one line and the two USB-ports are just a hub.

Is it right that a model A with an external 3x hub and a USB-ethernet should have the same USB and ethernet speed like B?
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by RaTTuS » Thu Apr 26, 2012 11:45 am
yes - in theory though model A's are not yet available

though I do have a use for them
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by Lob0426 » Thu Apr 26, 2012 7:50 pm
Yes you are correct. The model A just routes around the USB hub chip. Depending on the hub it might be faster than the chip (LAN9512) in handling the traffic into the USB. There are a couple of powered hubs that have an Ethernet adapter built into them. The question is what chipsets are supported by the kernel of he software you wish to use. The wiki has some listed. I hope people will be able to expand this list now that some RasPii are out in the world.
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by Techmeology » Fri Apr 27, 2012 2:24 pm
The simple answer is yes, however there are a few caveats:

If you had high bandwidth requirements over both the USB and the Ethernet then a bottleneck might appear sooner than with a dedicated Ethernet port. Ethernet via a USB device might also consume more CPU time.
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by plugwash » Fri Apr 27, 2012 2:37 pm
If the model A was available i'd be very tempted to get one and pair it up with http://cpc.farnell.com/unbrand.....b+ethernet . I've had less issues with the ASIX chipset in that device than with the SMSC chipset used on the Pi and 2 USB ports really isn't enough for my liking (three is the magic number IMO, one for keyboard, one for mouse, one for storage).

I'm also hoping that the PSU that comes with that USB hub with ethernet will be sufficient to power the Pi and some USB devices (it's supposedly rated at 2.5A but I haven't tested if it can actually deliver that while maintaining an acceptable voltage).
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by rew » Sat Apr 28, 2012 11:53 am
Techmeology said:


If you had high bandwidth requirements over both the USB and the Ethernet then a bottleneck might appear sooner than with a dedicated Ethernet port.


What "dedicated ethernet port"? The BCM2835 SOC on the raspberry pi does not have any "bus" except for USB. So the model B has a single chip: two port HUB + LAN soldered on the board. That is how you get two USB ports and Ethernet on the model B.

Adding a hub and an USB-Ethernet dongle on the model A is exactly the same as the Ethernet and hub on the model B.

The only differences are:


  • Model B has a LAN9512 hub/Ethernet chip. You can choose your hub and Ethernet chip if you start with a model A.

  • The lan9512 on the model B works, you'll have to check if whatever you choose works on the model A.

  • Whatever you choose on the model A might have slightly higher or lower performance than the lan 9512 on the model B.  


So: Some plusses some minusses. You choose.
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