Re: [Discuss-gnuradio] different decimation rates on one USRP

[Brent M. Ledvina]

On Sep 4, 2007, at 2:11 PM, Matt Ettus wrote:

Brent M. Ledvina wrote:

Hi,

I am running into a USB bandwidth issue. I'm sampling data

simultaneously from 2 daughter boards at a decimation rate of 10. This

produces 2*6.4 MS/s * 4 bytes/I and Q sample = 48 MB/s.

Actually, the correct calculation of data rate is:

6.4 MS/s * 2 * 2 = 25.6MB/s

One factor of 2 is for I and Q.  The other is for 2 bytes per sample,

since 16 bit samples are sent over the USB.  They are converted to

floats on the host computer.

So, for two daughter boards, I'd expect twice your calculation: 51.2 MB/s. 

My application requires one board to have a decimation rate of 10, but

the other can have a decimation rate of ~30. My understanding of the

USRP is that you cannot easily (i.e. in software) use different

decimation rates for different daughter boards on the same USRP. My

questions are: 1.) Is this easy to do at the FPGA level? 2.) Has

anyone tried this before?

It is not possible with the default FPGA build to use different rates

for 2 RX streams.  The TX and RX can have different rates though.

In your judgement, how challenging is it to modify the FPGA build? I could tolerate hardwired decimation rates.

Matt

-----------------------------------------------

Prof. Brent M. Ledvina

Assistant Professor

Space @ Virginia Tech

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