Re: [Discuss-gnuradio] Quick update

[Eric Blossom]

On Thu, Aug 05, 2004 at 11:52:44PM -0500, David Carr wrote:
> Quick update,
> 
> I've figured out the first problem.  Now I guess I need to learn a bit 
> more about this whole interface / alternate interface thing...
> 
> Nextly,
> 
> /test_fusb -iv
> Looking for SSRP...
> found.
> Opening RX interface...
> done.
> transfered 5.37e+08 bytes in 13.3 seconds.  4.045e+07 bytes/sec.  cpu 
> time = 1.39
> 
> 40.45MB/sec !!!!!!??????
> Am I dreaming here?  Also, is the CPU time in seconds?

This could be possible.  Yes, the CPU time is in seconds (DMA is your
friend).  In theory, the USB can do 50+ MB/sec, but the demo firmware
I've seen that got that speed was effectively a nop.  

In our code, the best I've seen is about 32.7 MB/sec, but we're
polling the FPGA to see if it's either got room for a packet from us,
or if it's got a packet for us.  If either of these are true, we set
up a GPIF DMA xfer and wait for it to complete.  We also watch the
FPGA and see if it's indicating overruns or underruns, etc.

> FYI, here's what dmesg says about my USB controller:
> 00:1d.0 USB Controller: Intel Corp. 82801DB (ICH4) USB UHCI #1 (rev 02)
> Other than that, 2.4Ghz Pentium 4, 640MB, Linux version 2.4.26-gentoo-r3
> 
> -DC

Eric