Hi,
On Thu, 2004-10-28 at 13:25 -0700, Eric Blossom wrote:
> We built an FX2 based software radio peripheral and we routinely
> sustain 32MB/sec in either direction. CPU consumption is minimal --
> on the order of 5% of a 1.4 GHz Pentium M. We did it all in user
> space using libusb, with an added layer on top that does "fast usb" by
> keeping multiple URBs in flight using usbdevice_fs.
>
> You can find all the code including the firmware and the fast usb
> library (fusb*.{h,cc}) at ftp://ftp.gnu.org/pub/gnu/gnuradio/usrp-0.5.tar.gz
I had a look at the fusb* stuff in your usrp-0.5.tar code and I have
some questions:
1. looks like every byte transfered with your "fast usb" lib is
memcopied at least two times: in your fusb*.cc code and in the usbfs
kernel code, right? Meaning worrying about sg-list "optimized" drivers
is sort of unnecessary...
2. with your "bypassing" of the libusb by accessing the fd inside the
usb_dev_handle and queuing multiple urbs at once, you do what Johannes
meant by
> We can go even further by using multiple URBs and queuing
> them, but libusb doesn't currently do that.
?
3. if I would use your fusb* code in a proprietary app, I would clearly
violate the GPL, right?
4. would it be possible to somehow migrate your fusb code/ideas into
libusb (changing from GPL to LGPL), thereby allowing me to profit from
that code? I would be glad to help here (my only option is to write
yet-another kernel driver :-/). Maybe this could be combined with what
Duncan Sands just posted, namely to use sg-lists to avoid the
unnecessary memcopies to further increase performance?
Thanks,
Axel
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