Yes, I'm using the $150 board sold by Xilinx and Digilent. The XC3S500E seems to have just enough logic and memory for this application, but the starter kit power supplies aren't very clean when you're digitizing signals in the low HF range. I'Il use custom hardware with linear regulators when I have a complete modem running on the starter kit.
We have similar ideas on the overall architecture. The Spartan-3E seems to be about 25% faster than the Spartan-3 and Xilinx now supplies FFT IP that uses only 2 block RAMs for a 512-point FFT. Consequently, you can do more with an inexpensive FPGA. Since I've always been interested in CPU architecture, I spent a lot of time on the soft CPU and need to move on with the rest of the project. It's just so easy to tweak the Verilog code and try different architecures and instruction sets. Much easier than my first experience in the early 1970's with MSI TTL. 73, John KD6OZH ----- Original Message ----- From: Paul L Schmidt, K9PS To: digitalradio@yahoogroups.com Sent: Monday, August 04, 2008 23:15 UTC Subject: Re: [digitalradio] Has anyone looked into FPGA-based digital modes? I hadn't thought of trying a high-speed VHF/UHF modem :) Maybe that's because I live away from what most people call civilization and there aren't many VHF/UHF signals around here. I'd figured on using a CPU personality for overall control, and doing the "work" in hardware. Is the Spartan-3E starter kit (Digilent/Xilinx) the one you're using? 73, - ps John B. Stephensen wrote: > The ADC and DAC are certainly adequate for audio so it will work. > > I've been interested in VHF and UHF high-speed modems so I have > a starter kit outfitted with a high-speed ADC and DAC that plug into J3. > So far I've tested the DDS and am in the middle of testing the second > version of a 16-bit soft MCU. After that, I have a lot of Verilog code > imported from a Spartan-3 project and converted from ISE 7 to ISE > 10 that needs to be integrated and tested. That should eventualy result > in an OFDM modem that operates at up to 2 Mbps. Real-time signal > processing is done in dedicated modules for filtering, FFT and CORDIC, > but in this design the soft processor is to handle everything between > the FFT and the Ethernet port. Think of it as an Intersil HSP50214 plus > an FFT and MCU in one FPGA. > > The soft MCU would probably be enough to process 8 ksps audio for a > modem as it has a MAC instruction. 3 or 4 would fit in an XC3S500E. > > 73, > > John > KD6OZH
