on FPGA simulation

I think you're missing the point. The problems start when part of the design will not (and isn't suppoed to) fit in any FPGA (or even any FPGA supported by the tools you're using). Perhaps you want to have a significant amount of memory. Perhaps so much that you cna't get an FGPA that will hold the logic _and the memory_. No problem in the real hardware, you conenct a memory chip to the FPGA. But a lot of FPGA_specific simulators can't handle that. It gets worse if the external memory is somplex to talk to, like many forms of DRAM. Trying to simulte a DRAM _inside an FPGA_ and have it fial i nthe right ways if the timing is wrong, just so you can simulate the DRAM controller you were designing in the first place is fraught with problems. Then there's the time you wnat to link your PFGA circuit to some external devies. Suppose you're designing a disk controller for a PDP11, anf you want it to use DMA and interrupys. I hardlly think you should try ot desing a UUnibus or Qbvus arbitor in the simulator just so you can test your deisng. And yet many, many, simulators can't handle tie idea of 'If you get this signal form my circuit, then assert this one 100ns later, then wait for my cirucit to assert this...). Or if you have an external device that accepts and produces a bitstream of some kind. Simulating that is always 'fun'. Somebody already mentioned genrating video signals in an FGPA. I don';t know about you, but I can't look at the waveforms going into the DACs (which is waht a ismulator is most likely to show) and see what the image will look like. Of course anythign weith ADCs or DACs is goign to be a problem. -tony