[Discuss-gnuradio] usrp2 master clock modifications

[Juha Vierinen]

Hi,

I tought I'd share some experiences with running the usrp2 system
clock with something else than 100 MHz  (so I can google it when I
forget).

Matt suggested that I could remove the 100 MHz oscillator and input my
own external clock instead. The VCTCXO was easy to remove, and I put a
1 Vpp sample clock in the place of pin 3. Another option would have
been to buy a VCTCXO with another frequency, but I just thought this
would be more straightforward.

I also modified the following places:

firmware/microblaze/lib/memory_map.h:#define MASTER_CLK_RATE 100000000
firmware/microblaze/divisors.py:master_clk = 100e6
lib/usrp/usrp2/usrp2_iface.cpp:    double get_master_clock_freq(void){

and flashed the firmware after compiling.

I initially tried with a 60 MHz clock. The, but I couldn't get the
sampling to start. I then tried 80 MHz with better success. The seems
to work ok, but I'm still in the process of verifying it.

juha

On Mon, Aug 16, 2010 at 16:35, Matt Ettus <address@hidden> wrote:

> The USRP2 can ran at other clock frequencies, but only by removing the clock
> on the board.  The oscillator on there is a CVHD-950 and it is available in
> a bunch of other frequencies in the range you are looking for, including:
>
> 67.5 MHz
> 70
> 74.1758
> 74.25
> 76.8
> 80 MHz
>
> You can also use the 122.88 MHz version and set the clock gen chip to divide
> by 2, to give you 61.44.
>
> See here for ordering:
>
> http://www.mouser.com/Search/Refine.aspx?Keyword=cvhd-950
>
> You can't make the reference clock appear on the output except by board
> mods.  If you are in a hurry and can't get a new oscillator chip, you can
> remove the oscillator and input an external signal.
>
> Matt
>