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Re: [Discuss-gnuradio] d_usb_data_rate

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] d_usb_data_rate
Date: Wed, 18 Jan 2006 23:14:53 -0800
User-agent: Mutt/1.5.6i

On Wed, Jan 18, 2006 at 05:56:02PM -0700, David R. Palchak wrote:
> I noticed that the usrp_basic constructor initializes a
> member variable called d_usb_data_rate to a value of
> 16,000,000 (host/usrp_basic.cc:109).  The comment on the
> line simply says "// SWAG".  What does this comment mean? 

Scientific Wild-Assed Guess

> How was the value of 16M chosen?

It's a typical value, 1/2 of our best case.

> It is possible to increase this value and thereby boost the maximum
> throughput to the USRP?

No.  This value is used only to figure out how often to poll for under
and overrun events.  It's set to the "right answer", by calls to
set_interp_rate and set_decim_rate in the derived classes,
usrp_standard_tx and usrp_standard_rx.  The default provided in the
constructor is used in the event that somebody else derives a new
class from usrp_basic and forgets to call set_usb_data_rate.

The call has to be made from the derived classes, usrp_standard_* and
not usrp_basic, because usrp_basic has no clue as to the signal
processing algorithms implemented in the FPGA, while usrp_standard_* do.


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