[Discuss-gnuradio] Re: usrp fpga possibilities and tvrx specs

[Eric Blossom]

On Mon, Aug 15, 2005 at 08:07:55PM +0200, Martin Dvh wrote:
> Hi,
> Is it possible to tell the usrp to only send 8 or 10 bit samples or only 
> the real part of the signal.
> (Is this at all possible with the current firmware?)

No.  This would require changing the verilog and possibly a bit of
host library code.  The FX2 firmware should not require any mods.

> Or is there any documentation of the blocks in the fpga code and the 
> usb-controller firmware and how to use them.
> I looked at the usrp manual and the usrp sourcecode but it is still not 
> clear to me.

usrp/fpga/toplevel/usrp_std/usrp_std.v is the top level of the verilog
usrp/fpga/sdr_lib/*.v is the library

> background:
> I am working on the TV code and other high-bandwidth blocks and am having 
> usb bandwidth problems.
> (I can't get anything without gaps above 4 MSPS complex 16 bit, even with a 
> straightforward dump to a ramdisk)

That's a problem with your usb host controller, not the software.
We really can do 32MB/sec (8 MS/sec complex) on many modern systems --
primarily those with the USB host controller built into the
motherboard chip set.

> I would like to be able to get only 8 or 10 bit samples over the usb bus or 
> only the real part of the complex signal (or the abs of the complex signal))

Getting just the real part wouldn't take too much hacking and would be
useful for porting the HDTV code too.

> If you know any tricks to get the linux-usb driver to deliver more bandwith 
> then I would also like to hear.
> (I read that only the intel usb2 host-controller can deliver 32 MB/s)

I suspect that pretty much any of the latest motherboard
implementations will handle it, but I don't have data to support this 
hypothesis.

> I have looked in the usrp driver code but did't know where to look.

The formatting of the data is all handled in the FPGA.  The FX2
firmware doesn't even see the bulk data going in and out.  It's DMA'd
to/from the GPIF from/to the USB buffers

> I would also really like to find a copy of specsheets and application notes 
> of the microtune tuner in the tvrx. The pdfs seem to be removed of the 
> microtune site.
> (especially the gain-control and exact (if and second if) filter 
> characteristics information for building a tvrx agc and videofilter)

Here you go:

  http://comsec.com/usrp/microtune/4937-DI5-3x8899-2.pdf
  http://comsec.com/usrp/microtune/NF_tutorial.pdf

Eric