I really banged my head on this one: I was sure I had set up all registers correctly, and still I got complete garbage at the output. Or, as some investigation showed, everything worked OK, only the PLL didn’t seem to do anything: The VCO was stuck at its lowest possible frequency (which depended on [...]
I simulate models outside of the Xilinx’ IDE (known as ISE), since the simulation is textual anyhow. Besides, running regression tests without being sure the simulation settings are repeated exactly is a good way to waste time every time the mouse clicks without our full awareness. Anyhow, my problem was that I instantiated a Xilinx [...]
OK, so the board designer just sent me an updated schematics of the design. Are there any changes? Comparing the schematics itself is hopeless. So I’ll compare the PCAD netfiles (those with a .NET extension). I mean, they are simple text files, after all. The problem is that Orcad feels free to change the order [...]
Having a pretty large state machine, I wanted the states enumerated automatically. Or at least not do the counting by hand. I mean, doing it once is maybe bearable, but what if I’ll want to insert a new state in the future? So what I was after is something like module main_state #(parameter ST_start = [...]
The problem Sometimes software packages require setting some environment variables for its proper execution. When these variables clearly have no effect on any other applications in the system, that’s fine. When they want to manipulate some sensitive variables, which other applications may depend on, that’s a whole different story. When it’s a single executable, the [...]
Introduction I’m using Xilinx’ MiG 1.7.3 for running DDR2 memories on a Virtex-4 FPGA. It didn’t take me long to realize that the controller never finishes initialization. The problem is that I had no idea of why, and as far as I know, no documentation to refer to in my attempts to understand where the [...]
The whole story began when I decided to be kind enough to tell the Xilinx tools (ISE 9.2 in my case) that the Virtex-4 I’m targeting is a grown-up. Stepping 2, to be precise. I added CONFIG STEPPING = “2″; to the UCF file. It must have been one of those moments where I believed [...]
(…or why the Verilog-emacs AUTOARG is redundant) In Verilog, I never understood why port declarations appear both in the module declaration, and then immediately afterwards, along with the wires and registers. I mean, if the ports in the module declaration are always deducible from what follows immediately, why is the language forcing me to write [...]
Surprise, surprise! When porting a design from Spartan-3 to Virtex-4, I discovered that many registers, which were correctly placed in the IOB in the Spartan-3, fell off into fabric-placed flip-flops. Which is very bad news, since keeping the registers in the IOB isn’t just a matter of better timing, but rather repeatable timing, which is [...]
The problem: NGDBUILD tells you it can’t find a net or instance given in the UCF file. It’s likely that the synthesizer changed the names, sometimes slightly and sometimes beyond recognition. You need these names to define a timing group, for example, but how do you know them? Normally, I would get the net and [...]
