Re: Looking for a VHDL forum or individual help

From: André Fachat <>
Date: Fri, 20 Aug 2010 23:27:38 +0200
Message-ID: <>
Also may be interesting for you:

I am using Xilinx' ISE Webkit 11.1 for the normal VHDL development. It is the only one I know so I cannot compare, but, well, it works.

But what I found really useful: I am keeping my VHDL ghdl (GNU vhdl compiler) compliant (i.e. not using specific Xilinx features) and use ghdl to simulate the VHDL and watch the results with gtkwave. This way I can check my designs even before programming them into the hardware, which speeds up turn-around times a lot.
(I haven't gotten to do actual simulation with ISE Webkit so far though, if you have any pointers, might be worth a try)

For the simulation I am writing additional VHDL that simulates a workbench, i.e. mostly a stripped down version of the actual computer the programmable part is in. I am using free6502 as CPU core for example. Although it is not cycle-exact, it provides me a "good enough for me" alternative for the VHDL debugging.

I write this because just now I have actually found a bug in my pet816 card - just by trying to make the VHDL workbench more exact (for details: I have a hardware address comparator connected to the slow bus, but in the VHDL I assumed it being on the fast bus, which gave strange effects - you could poke the CPU card into a specific state, but not back afterwards. I found the problem when I had to write the VHDL code for the address comparator emulation and suddenly had to think about which bus it uses. a few minutes later the bug was fixed... :-)

I'm writing something up about this for the next release of the PET 65816 card, which should - now as this bug is fixed - hopefully happen this weekend


-------- Original-Nachricht --------
> Datum: Thu, 19 Aug 2010 21:15:11 +0200
> Von: "André Fachat" <>
> An:
> Betreff: Re: Looking for a VHDL forum or individual help

> I'm reading "The Designer's Guide to VHDL" as well. Although, the book has
> a few centimeters in thickness, and my bookmark still counts only
> millimeters :-)
> But I've already jumped ahead and looked for (and found) stuff I needed in
> my project. So far I think it's ok.
> André

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