I need to build a sort of a simple video processor to drive a TFT LCD screen in an embedded system. The plan is to use a small and cheap FPGA with some memory. Low cost is very important, so fast SRAM is not an option.
I want to test the concept on an off-the-shelf board before making my own, so I got the Spartan 3E "starter kit" that comes with DDR SDRAM. Unfortunately I can't make the memory work using the core generator. Most likely I'm not doing something right, but maybe there is some problem with the hardware.
While searching for info on SDRAM interfacing I got an impression that the DDR SDRAM is very difficult to use and the board layout is very critical. For my application 133 MHZ DDR is a heck of an overkill as I only need to read 16 bits of consecutive data at 50 MHz (burst) max.
So regular SDRAM is probably a better choice. I'm also using Micron SDRAM elsewhere on my device (with the PXA255 CPU).
Looking for a board with built in SDRAM I came across the $150 Altera DE1. Traditionally I used X more than A, but those were CPLDs rather than FPGAs. The data sheet looks promising. Only 2 power voltages. Same cost (Cyclone 2 vs. Spartan 3e).
There is also PSRAM as an option and a Digilent board with S3e and PSRAM, but it is more expensive than plain SDRAM by far.
My volume is about 10,000 a year. I figure about $5 for FPGA and $1.5 for SDRAM (8 MB). PSRAM is more like $5.
Am I missing something? I'd like to hear opinions before making the next move.
Thanks.
-Alex.