Anyone use HDL as design tool for PCBs?

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Hi,
   Does anyone out there in usenet-land know of tools to let you design
Printed Circuit Boards with VHDL? I'm ready to switch from schematic entry,
I want portability! (And all the other good reasons I switched from
schematic entry for my FPGA designs) Anyone use a PCB layout tool that
accepts EDIF files? I see there are translator tools. Anyone ready to share
their experiences, pitfalls et cetera?
        thanks for reading, Syms.



Re: Anyone use HDL as design tool for PCBs?

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Features like pin swapping, gate swapping and cross probing will only
work with a tightly integrated pcb and "source" toolset.

I suspect you would lose this with an HDL front end, although they do
seem possible in theory.


Frankly, the thought of designing a switchmode power supply using an
HDL scares me.  Designing a microstrip filter using an HDL seems nigh
on impossible.
(Hint: both these applications require careful layout, which is
something that can be more easily expressed with a graphical entry
tool.)

Regards,
Allan.

Re: Anyone use HDL as design tool for PCBs?
Hi Allan,

I tend to agree with your opinions. I just wanted to add that PCB layout
tools that generate VHDL/Verilog netlists are very useful for system level
simulation. Obviously this is not the information the original post was
attempting to obtain but I wanted to throw it out there for others to
contemplate.

Matt


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Re: Anyone use HDL as design tool for PCBs?

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Matt, it is true that they are useful for system level simulation. But
the way of the development is IMO just the opposite: _first_ you do a
simulation, also on system level, _after this_ you design your chips and
board. For the system level simulation you need a HDL entity, like
¨Board¨ that connects the HDL Units representing the chips. You can do
this by the Testbench unit, but IMO it is a better approach to separate
the testbench and board functions. And you are there: you have a ¨Board¨
HDL that contains all inter-chip connections, it would be perfect to use
this for PCB Netlist generation.

I made already a try with this, but did not succeed.

Janos Ero


Re: Anyone use HDL as design tool for PCBs?
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Janos --  agreed on the system simulation up front.


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Agreement here as well. However I am not talking about Board = Testbench.
Let me clarify. :-) "Board" is what I am talking about. Here testbench
instantiates the "board" which instantiates "chips", resistors, capacitors,
connectors etc. The tools generate "Board" from either a schematic capture
tool or more importantly, the PCB tools. The reason I would prefer PCB tools
is that if there are problems in the layout these could be detected in the
simulation. All of this is automated to reduce human error. The things that
you can catch are those things that DRC normally doesn't catch like
incorrectly wired connectors and components.

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I am talking about the opposite approach. PCB netlist is used to generate
"Board".

-- Matt






Re: Anyone use HDL as design tool for PCBs?
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Hi Allen,
    Thanks for the reply! The tool I use at the moment, ORCAD, has separate
layout and schematic entry bits. So, I agree that layout, i.e. drawing the
traces, makes no sense in VHDL. However, the schematic entry is a pain in
the @rse, after all it's just wiring up components to each other. You end up
typing in lots of attributes anyway, part numbers, value, package size, pcb
footprint. Seems to me that the physical wiring of the parts is perfectly
feasible in HDL, and I can use Perl scripts to speed things along, like I do
with VHDL for my FPGA innards designs. Maybe for some things like a SMPS, a
diagram is very useful, perhaps necessary. However, for connecting a DRAM to
a FPGA, the picture adds very little if anything. Some kind of hybrid is
called for, like we already can do with logic inside FPGAs.
    Also, I would expect a HDL to be just as good at pin-swapping / gate
swapping, but, once again, I agree that layout remains inherently graphical.
As you point out the geometry of the traces is vital, and often forms part
of the circuit.

    Anyway, back to ORCAD!
            cheers, Syms.



Re: Anyone use HDL as design tool for PCBs?
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I agree completely with you about the advantage of HDL for "schematic
capture".  Typically when you design a digital circuit you are making
lists of bus names that connect to pin names or numbers... you just do
this graphically rather than in an editor.  This is actually more work
of course, than just making the list as text.  But most people are
"comfortable" with schematics.  The advantages of using schematic with
layout really comes from the shared library rather than any inherent
feature of schematic capture.  

I remember a coworker who was telling me about a project from "hell" he
had worked on at his last job.  He inherited the work from a designer
who had left and the docs were text lists of pins to nets, NO
schematic!  This guy could not work that way and ended up doing very
poorly on that project.  

Besides, isn't a schematic a nice thing to look at?  Well, maybe not...

Would you be willing to write your design in a PCB program's netlist
format?  If you pick one that is popular (like PADS), it is portable in
that most packages will import it.  

--

Rick "rickman" Collins

snipped-for-privacy@XYarius.com
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Re: Anyone use HDL as design tool for PCBs?
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I agree completely.  Keeping track of 300+ FPGA user I/O pins is hard
enough in a spreadsheet or HDL.  It's pretty much impossible on a schematic.
Integrating the FPGA design and board design also has to be a Good Thing.

        - Larry   [who would s/VHDL/Verilog/g in the above]

Re: Anyone use HDL as design tool for PCBs?
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 You are actually looking for a hybrid - as you say R's and C's do not
HDL well.

 The NETLIST formats of most PCB systems is quite simple, and some
import many
variants.

 Better packages allow you to MERGE and CHECK netlists (ie split
imports), so you
could create a Analog Schematic + Block structure/IC number in
Schematic (to keep BOM correct) and then move to HDL for digital
interconnects.

 If the device ( eg U1 TQFP100 ) is already imported via the SCH leg,
all your HDL->NET has to do is handle the PinNumber -- NetName
collections.

 That should not be too hard for someone used to scripts.

 You can also go backwards - eg after PINSWAP, a PCB script can create
the
PIN - Name list in the HDL format, for manual paste.

 -jg

How do you keep layout info in VHDL?
I was always considering VHDL as behaviur/logic (netlist on functional
gates) specification language. There are no means to add more detales
required at PCB layout abstraction layer. VHDL has no means to describe
placement, traces and device packages. I'm I missing missing something?



Re: How do you keep layout info in VHDL?
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In principle, all this information could be stored in VHDL
attributes.  Attributes were designed for precisely this reason -
attaching information to a VHDL object that makes no sense in
VHDL, but must be passed to other tools.  In practice, however,
the result would be a disgusting mess.

Stick with a decent schematic package that can generate
a VHDL netlist.  Use that VHDL netlist for your pre-layout
functional simulations, and use the conventional
schematic-to-PCB tools for layout.
--
Jonathan Bromley, Consultant

DOULOS - Developing Design Know-how
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Re: How do you keep layout info in VHDL?
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I think the part you are missing is that Symon wants to replace the
schematic portion of the PCB layout software. I does not look to me like
he was talking about replacing the layout portion. Maybe some people put
layout info on the schematic, but I think most do not.

--
My real email is akamail.com@dclark (or something like that).


Re: How do you keep layout info in VHDL?
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Thanks Duane, you've got it exactly! I re-read my OP and can see I wasn't
too clear! (Ah, the perils of posting at the end of a busy and frustrating
day!!) I've posted again to try to clarify what I'm banging on about.
Cheers, Syms.



Re: How do you keep layout info in VHDL?
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I agree that the "netlist capture" portion of
PCB schematic capture could be more easily done
with vhdl or verilog. I like to look at
a schematic too, but let's have the machine
draw it!

Most large digital components have a free
vendor-supplied BSDL file that could be
converted to an entity with a script.

All of the architectures could be null
for the purpose of netlist capture.

The top_pcb.vhd file would be formatted
like a testbench with all of the
signal (wire) declarations, entity
instances, and port maps.

A simulation compile could find
unintended shorts and opens, and
a viewer could display a schematic
for checking wires and entity instances.

A script could process top_pcb.vhd
to create a netlist compatible
with PADS, Allegro etc for layout.

The top_pcb.vhd file could be used
again when the fpgas code is complete
for a board level digital simulation.


  -- Mike Treseler






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