Re: [Xylo-SDR] Architecture review

[Lyle Johnson <kk7p@wavecable.com>]

> A FPGA can make a DSP look like a sick puppy, that is one reason I 
> recently bought a Spartan 3 1000K board, 24 multipliers in hardware 
> built in. I looked for examples and found a 4096 point FFT using 
> floating point in 7.6 microseconds, is that fast enough? We would not 
> need it anywhere that fast so we could cut back on the hardware usage.

FPGA-based DSP is useful for certain applications where lots of speed is 
needed for a straightforward algorithm, like the FFT you cite. 
Real-time video filters, etc., are fertile ground for FPGA-based DSP.

But it is very difficult to fit into the same FPGA -- running at the 
same time -- a denoiser, adjustable filters for SSB and CW, a Tx 
equalizer, impulse noise blanker, SAM tracking demodulator...

A general-purpose DSP is useful for applications that require a bit less 
raw horsepower but great flexibility in the algorithms being performed.

A good example is the SDR-1000.  The DSP being done in the code running 
on the PC would likely be be a nightmare in an FPGA, unless you created 
a "soft" programmable DSP inside the FPGA, but that's cheating...

I create designs with DSPs and FPGAs, and use both extensively.  Each 
has its place -- I want to be sure there is a place in the "not Xylo no 
acronyms sorta universal widget box" being discussed, even if that place 
is never occupied :-)

73,

Lyle KK7P