umtrx fpga internal clocking

Josh Blum josh at joshknows.com
Wed Apr 9 17:43:25 UTC 2014



On 04/09/2014 03:17 AM, Andrew Karpenkov wrote:
> Josh,
> I'm glad that I answered on most of yours questions. If you need some more
> information, don't hesitate to contact with me.
> 
> 104MHz fifo bus in -> cross clock fifo to 26 MHz -> vita tx deframer ->
>> paced tx dsp -> out to dac
>> in from adc -> paced rx dsp -> vita rx deframer -> cross clock fifo to
>> 104 MHz -> 104 MHz fifo bus out
> 
> 
> According to your idea. I think that this is fine, but are you're sure that
> 26MHz is enough for DSP calculations? In N2x0 DSP clock frequency was twice
> higher than CPU clock.
> 

Well technically, the DSP only needs to run as fast as the ADC/DAC
sample rate. In the current UMTRX design, the DSP calculations
themselves are running at 13 MHz. I'm only suggesting moving the VITA
framer/deframer into the same clock domain as the DSP units (26MHz). The
actual buffering, packet routing, fifo muxing, that sort of stuff will
stay in the 104MHz clock domain (it has to be faster because of
buffering/sending ethernet packets). And the CPU/ZPU/wishbone clock is
independent, and really only for low speed communications -- I would
simply keep this at 52 Mhz, but in fact, its clock rate isnt really
critical.

-josh




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