Re: [Discuss-gnuradio] Attaching 2 USRP sets to one PC

[Eric Blossom]

On Fri, Jan 26, 2007 at 06:49:54PM +0100, Raphaël Jacquot wrote:
> Eric Blossom wrote:
> >On Fri, Jan 26, 2007 at 11:23:17AM -0600, Michael Ford wrote:
> >>I feel like I've seen this question asked before, but is it possible to
> >>attach two USRP boards to the same PC, and transmit between the two?
> >>
> >>-Michael Ford-
> >
> >Yes it is.
> >
> >The first argument to the usrp constructor, which, says which one you
> >want to open (0, 1, ...).  The interpretation of "which" is OS and libusb
> >dependent and is kind of vague.  Last time I checked, I believe that
> >it was a function of the order that the devices were connected.
> >
> >Another approach is to open each one, then check the serial number to
> >see if it's the one you want.
> >
> >  s = u.serial_number()   # returns a string
> >
> >Also note that the total USB bandwidth of the system (on the order of
> >32MB/s) is shared by all attached devices.
> 
> unless you connect each to a separate port on the machine
> in which case, you have a full bandwidth for each.

In almost all machines I have seen to date, there is a single EHCI
host controller that connects to all ports on the machine.  The
bandwidth limit is the sum across all ports connected to a given EHCI
controller.  (The one exception I have seen is a dual processor
Opteron motherboard based on an nVidia nForce4 chipset.  It
effectively has two southbridge chips, each of which contains a USB
EHCI controller, SATA, etc).

You can determine how many ECHI controllers your machine has by
examining the output of lspci:

  address@hidden ~]$ lspci | grep -i usb
  00:1d.0 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI #1 
(rev 02)
  00:1d.1 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI #2 
(rev 02)
  00:1d.2 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI #3 
(rev 02)
  00:1d.3 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI #4 
(rev 02)
  00:1d.7 USB Controller: Intel Corporation 82801G (ICH7 Family) USB2 EHCI 
Controller (rev 02)

One EHCI controller and 4 associated UHCI controllers.

Eric