[Open-graphics] PCIe know-how?

[James Richard Tyrer]

Daniel Rozsnyó wrote:
> OGP does not do PCIe (yet). Only PCI and PCI-X.
> 
> Anyway, for your instrument I would suggest interfacing it to USB2 if 
> you can offload the processing to dsp/fpga, but that won't be under 
> $100. For such a price you can get an ADC and a PCIe interface, but then 
> you will have troubles with processing the 500+ MB/s of data in realtime 
> on the PC's CPU..

I don't think that it would need to process this much data per second. 
A spectrum analyzer, like a digital oscilloscope, does not deal with 
real time data but rather with a periodic signal.  To be more specific, 
a digital oscilloscope displays a periodic signal on the screen and the 
refresh scans rather slowly from left to right.

Actually, a spectrum analyzer is *only* software that takes as input the 
digitized output of a digital scope.  The software can either use the 
FFT or can obtain the Fourier coefficients by numerical integration. 
The only difference in the hardware is that it would be best if the scan 
frequency could vary to display exactly one cycle -- which means a 
variable sample clock and a PLL.

So the question is whether you can make a good PC card digital 
oscilloscope for $100.00.  You need an oscillator, frequency divider, 
PLL, sample & hold, and DAC as well as the PCIe interface.  I seriously 
doubt that this is possible for $100.00 but it does depend on the 
maximum input frequency you wish to use, sample rate, and the accuracy 
(and number of bits) needed.  Actually, you can spend over $100. on a 
good DAC

-- 
JRT