Re: [Discuss-gnuradio] external clock question

[Eric Blossom]

On Thu, Nov 30, 2006 at 11:22:05AM -0400, Ryan Seal wrote:
> I am using an external clock, currently at 64 MHz, but will drop to 50 
> MHz so I can place a 30MHz IF signal in the right spot for 
> down-conversion. Here is my question:
> 
> The file usrp_basic.h has the following member:
> 
> long  fpga_master_clock_freq <cid:part1.06060807.00030702@naic.edu> () 
> const { return 64000000; }
> 
> If I want my system to work at 50 MHz, will I need to change this constant? 
> Or add something like:

Yes.

> fpga_master_clock_freq(const long& freq) { master_clock_freq = freq;}

The other code calls fpga_master_clock_freq to determine the master
clock frequency...  FYI, Python doesn't deal well with multiple
functions with the same name, discriminated by argument types.  If you
want to add a method, I suggest calling it set_fpga_master_clock_freq.
You'll have to figure out the earliest place that
fpga_master_clock_freq is called, and ensure that you manage to set it
before somebody reads it.  It may have to be a static method of the
class that can be called before instantiating an instance of the class.

> I am guessing there might be a reason for this being a constant vs. a 
> variable?

The idea was that there was a single place in the code
(fpga_master_clock_freq) that "knew" the actual frequency.

> Thanks,
> Ryan

Eric