From: Martin Dvh <[EMAIL PROTECTED]>
To: Clark Pope <[EMAIL PROTECTED]>, gnuradio mailing list
<discuss-gnuradio@gnu.org>
Subject: Re: [Discuss-gnuradio] Run USRP at alternate clock frequency?
Date: Fri, 07 Apr 2006 00:06:55 +0200
Clark Pope wrote:
Update on status:
I purchased a 44 Mhz oscillator from digi-key (p/n 300-7254-1-ND,
CSX750FJC44) for $3.38. The first attempt to remove the USRP 64 MHz
failed miserably with a pen iron. I purchased a heat gun from digi-key
(MA1008-ND) for $52, set it to the 1000 degree setting and the old
oscillator came up in about 10 seconds. Installed the new oscillator and
checked the 44 MHz clock with a scope.
I then tried to run my customized dbs application that records 8-bit I/Q
data to a file for me from any of the 802.11b channels. Got all zeros in
the data. Then remembered eric told me to change the clock in
db_dbs_rx.py.
My code is a little older than current but here's my mods in
gr-usrp/src/db_dbs_rx.py:
1. change line 88 from
self.refclk_divisor = 16
to
self.refclk_divisor = 11
2. change line 108 from
return 64e6/self.refclk_divisor
to
return 44e6/self.refclk_divisor
then in /gr-usrp I did
make clean
make
make check
make install
Reran my custom dbs program and it worked fine EXCEPT:
The default decimation is 4 so I'm recording at 11 megasamples per second.
(oddly enough I'm still able to demodulate my 802.11b packets fine even
though the chip rate is 11 mcps!?) When I try a decimation rate of 2 I get
the message:
Will you be sharing this code?
I think more people will be interested in doing 802.11b.
I plan to but probably later this year. Right now I'm collecting on linux,
then processing on windows, and then running some utilities to get the
packets into ethereal. My goal is to have a single net interface under linux
that looks like any other.
I'd like to start an open source project on this maybe on sourceforge, but
I've heard mixed experiences. Any suggestions on a host is appreciated.
usrp_standard_rx::set_dim_rate: rate must be EVEN and in [4,256]
I am using the std_4rx_0tx.rbf fpga design. Is the min decimation really
4?
If necessary I will go modify that fpga to just have a halfband so I can
record at 22 complex megasamples per second which is enough bandwidth to
support 802.11a/g. Can't beat more bandwidth at less power.:)
It will be interesting to see if you will be able to get complex 8 bit
samples over the bus with decimation 2.
This will be 44 Mbyte/sec over the usb bus. This is within the theoretical
limits of usb2 but until now I have not heard of anybody being able to
sustain more then 32 Mbyte/sec over the bus using the usrp.
I will try today.
Greetings,
martin
Thanks,
Clark
From: Eric Blossom <[EMAIL PROTECTED]>
To: Clark Pope <[EMAIL PROTECTED]>
CC: discuss-gnuradio@gnu.org
Subject: Re: [Discuss-gnuradio] Run USRP at alternate clock frequency?
Date: Fri, 10 Mar 2006 13:48:52 -0800
On Fri, Mar 10, 2006 at 11:21:08AM -0500, Clark Pope wrote:
>
> I would like to run my USRP off a 44 MHz clock instead of the 64 MHz
clock
> that is currently used. A couple reasons:
> 1. the 64MHz rate exceeds the USB bandwidth even with byte-wide
samples
> (64*8 = 512 mbps)
> 2. 44 MHz works much better for the wlan signals I'm after
>
> So the questions are:
> 1. can I generate a 44Mhz clock from the 64 MHz or do I have to change
the
> crystal?
You need to change the crystal.
You'll also need to change the definition of
/*!
* \brief return frequency of master oscillator on USRP
*/
long fpga_master_clock_freq () const { return 64000000; }
in usrp_basic.h The rest of the code should follow, though I haven't
tested it. YMMV, patches welcome ;)
> 2. If I change over to 44 MHz will everything else still work?
Especially
> the dbs and flex2400 boards?
Not sure about those. Paging Matt Ettus, paging Matt Ettus...
Eric
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