Re: [Discuss-gnuradio] USRP E100 Product Announcement

[Matt Ettus]

On 11/23/2010 07:53 AM, Douglas Geiger wrote:
> What sort of connection exists between the Overo and the rest of the
> system (e.g. is this using USB, high speed serial, etc.?)? In
> particular what sort of bandwidth is possible from the
> ADC->FPGA->Gumstix. Obviously the larger FPGA allows for some extra
> signal processing to be done before the gumstix,

We use the General Purpose Memory Controller (GPMC) bus which is a 
parallel memory bus.  We have written a kernel module device driver for 
it, which the UHD talks to.

As for bandwidth, we currently get about 20 MB/s, which gives you about 
4-5 MHz of RF bandwidth at 16 bit samples.  This has not been optimized 
at all, so I wouldn't be surprised to get 50% more with a bit of tuning, 
but I can't promise anything.

The other thing to keep in mind is what you do with these samples in the 
Overo.  While the OMAP3 is a very capable processor, its performance is 
nothing like today's laptop computer.  If you are pushing high data 
rates, to really get the most out of the system you'll want to migrate 
some processing to either the FPGA or to the C64x+ DSP.

> but does the gumstix
> then see the mainboard as an USRP1-like source (i.e. 16-bit samples @
> 8MS/s), or is the bandwidth/bits-per-sample easily adjustable?

You would instantiate a UHD source and/or sink in your code, and so it 
would look like any of our other devices.  Using other sample sizes, 
like 8 bits per sample is possible, but will take a little bit of FPGA 
tweaking.  The nice thing is that because we are using a common FPGA and 
driver base across the USRP2, USRP N210, and USRP E100, the same tweaks 
will work across all of them.

Matt