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Re: [Discuss-gnuradio] Question on DDC/USB interface
From: |
Eric Blossom |
Subject: |
Re: [Discuss-gnuradio] Question on DDC/USB interface |
Date: |
Thu, 5 May 2005 12:24:18 -0700 |
User-agent: |
Mutt/1.5.6i |
On Wed, May 04, 2005 at 10:21:07AM -0400, Anastasopoulos Achilleas wrote:
> How are the 4 complex streams out of the 4 DDCs multiplexed into the USB
> port?
Depending on the nchannels setting you either get 1, 2 or (someday 4)
DDC outputs muxed onto the USB.
Assume that the DDCs are numbered 0, 1, 2, 3.
* If you select one channel, you get only the output of DDC 0
* If you select two channels you get one complex sample from DDC 0,
followed by one complex sample from DDC 1, etc
* If you select four channels you the one complex sample from DDC 0,
one from DDC 1, one from DDC 2, one from DDC 3, etc.
> If the 4 ADCs sample at 64MSps, and each of the DDC's is downsampling by
> N, then there are 4 complex streams of 64/N MSps waiting to be transfered
> through the USB port.
> How do we control (if we can control) which of the 4 is transfered ?
See above.
Note that you control which A/D's are routed to the DDC inputs using
the mux control word. See usrp_standard.h for docs.
Eric