I built a very similar circuit using an Altera FPGA and a 100MHz SDRAM with good results. To keep things easy, I did a couple of things. One, I kept the signals to the SDRAM as short as possible (around an inch long, in most cases). Second, I made sure that the clock that the SDRAM controller sees and the clock of the SDRAM have minimal skew. I did this by running the original clock into the FPGA and then running it out 2 pins. One went to the SDRAMs and the other went back into the FPGA, but the etch length was the same as the length that went to the SDRAMs. Then, I used a PLL in the FPGA to "look" at the arriving clock and skew it (which are really the output clocks) to match the clock of the SDRAM controller. That way, I could be sure that the clock that the SDRAM sees and the clock of the controller were the same. Without that, it's very hard to meet all the max/min setup and hold times of the SDRAM and SDRAM contoller.
Steve DJ Delorie wrote: >> That's what I'd do. At the sort of volumes you and I work with it's >> a lot cheaper to use a FPGA big enough to include >> chipscope/signaltap even in the full design than to allow for an LA >> hookup. >> > > I'm limited to QFP packages, though. I picked the 3A family for some > reason, ah, power - the 3A doesn't need a 2.5v interface block. > I haven't tried synthesizing into the 3A yet to see how much space I'm > using. > > >> Why not just use chipscope? I thought you could get that for free >> these days (although admittedly I use Altera mainly for free Signaltap >> myself). >> > > Well, if chipscope is freely downloadable, I'm OK with that. > > >> Hard to believe the LA expects signals that fast without active probes. >> > > Well, I said Ms/s, not MHz. It's mostly useful for measuring skew and > jitter relative to other pins. I usually run at one of the slower > speeds, as the LA's compression doesn't work at the fastest speed. > > > _______________________________________________ > geda-user mailing list > [email protected] > http://www.seul.org/cgi-bin/mailman/listinfo/geda-user > > _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
