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[Discuss-gnuradio] Using USRP from multiple applications simultaneously

From: Harald Welte
Subject: [Discuss-gnuradio] Using USRP from multiple applications simultaneously
Date: Sun, 1 May 2005 20:27:34 +0200
User-agent: mutt-ng 1.5.8-r168i (Debian)


AFAICT, at the moment there is no way to use a single USRP from multiple
application programs at the same time.  This is quite unfortunate, since
you might want to run a transmit and a receive program that are totally
independent (or even two tx and two rx programs).

While browsing through the usrp fx2 firmware and the low-level host-side
code, I learned that there are three seperate usb interfaces which one
endpoint each.  What was the idea of splitting control/in/out to
seperate interfaces? 

Wouldn't it be nice to actually provide multiple interfaces that each
correspond to a certain amount of USRP hardware?  This way each
interface can be claimed by a seperate program.

Seperating it into four interfaces (2rx, 2tx) might be complicated,
since there certainly are shared data structures and functional blocks.

Providing two interfaces (one for each AD9862) should be easier,
since full control over a singe AD9862 would be in one program.

I haven't yet looked at the FPGA verilog, but maybe you can give me some
comments on whether you think

1) this is a good idea (and was planned but never implemented)
2) there are any serious known issues (which?)

If it looks feasible, I would probably be looking into that issue.

I was also thinking of speeding up the USB data transfers by using a
better kernel/userspace interface than libusb (which does
copy_{from,to}_user for every URB).  Something like a mmap()ed
ringbuffer comes to mind, much like the mmap() feature of AF_PACKET or
the PF_RING socket.   But that's probably one of the things that would
be nice and I never find the time to implement...


- Harald Welte <address@hidden>                         http://gnumonks.org/
"Privacy in residential applications is a desirable marketing option."
                                                  (ETSI EN 300 175-7 Ch. A6)

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