Re: [Discuss-gnuradio] HDTV and the USRP

[John Gilmore]

> Wasn't one of the major requirements of the USRP to be able to handle
> [HDTV in real time]?

No.  The main requirement of the USRP was to make hardware that ordinary
people can buy and plug in, which is at least as capable as the $1200
PCI boards that were used in our early work (including the HDTV decoding).

The USRP is quite a bit more capable than the PCI board, will offer
better integration (with band-specific daughter boards and tuners, and
use with laptops), at a similar or lower price.  The catch is that it
has less bandwidth back to the host, because it uses USB2 rather than
PCI.  We're focusing first on making the USRP shippable for more
generic uses.  We didn't even want to get into the huge time sink of
designing and shipping hardware, but nobody else was building decent
cheap high speed A/D and D/A interfaces, so we succumbed to the
temptation.

It may be possible to reprogram the FPGA to process enough of the HDTV
signal that the data can be pulled back across the USB2 bus and the
remainder of the processing can be done in the host.  We'd love it if
*you* wanted to contribute work toward making the USRP work on HDTV
signals.  At the moment, evolution of the core GNU Radio
multithreading & USRP code has broken the old HDTV modules, even if
you have the old PCI board.  Fixing them to use the new interface
would be a good first step, if you want to help.

(GNU Radio's HDTV recording capability that we built last year did not
work in realtime; it took 40 seconds of computation to decode every
second of HDTV into an MPEG transport stream.  It also pushed data
thru the PCI bus so fast that it tickled bugs in some common
motherboard chip sets.  But we created open source code that can
reliably, if slowly, demodulate HDTV data streams.  This code can
later be used as a model for faster HDTV decoders, either in hardware
or in software.  Even if FCC gets away with outlawing open HDTV
hardware for the benefit of monopolists, this software cannot be
censored, either legally or practically.  (Archive and publish a copy
of it outside the US, if you're reading this from outside the US,
please!)  As hardware capabilities advance, it will become more and
more usable worldwide, even in repressive countries such as the USSA.)

If you just want to record HDTV, there are several cheap, dedicated
cards available for this purpose.  Buy them this year!  Next year the
FCC has mandated (if the courts don't overturn it) that any such cards
must enforce Hollywood copy-prevention crap (i.e. they won't give you
a plaintext digital signal).  See EFF's "Digital Television Liberation
Front" for details on the regs, and on the cards and software that
work today and will continue to work next year:

  http://www.eff.org/broadcastflag/

        John Gilmore