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RE: [N8VEM-S100:1465] S-100 board reorders

Hi Bill!  Thanks!  I use KiCAD for schematic capture and PCB layout.  I use FreeRouting.net for the PCB trace routing and optimization.  All of the PCB design information *including the tool chain* is completely open source/free software except for FreeRouting.net which is *free to use* but not open source/free software.


The general PCB design process is to design a schematic for your design (CPU board, IO board, etc) and capture it in KiCAD.  Make sure it has all the compatible connections and passes Electrical Rules Check.  Then generate a network file of all the connections, assign footprints to the parts, and then layout the PCB. 


I layout the PCBs to minimize the overall length of connections and minimize the number of vias.  Basically that’s just grouping like components in a circuit together.  For example, start with the bus interface and place what components are directly connected to it, then which are connected to those, and so on.  Sometimes I start with the CPU and work outwards but generally speaking it is a balance between the core component (IO device or CPU) and the bus interface.


The trace route optimization can take days to months depending on the design and how rigorously it is optimized.  The time required scales exponentially with circuit complexity.  For example a simple circuit like the SCSI-1 to IDE/SD bridge will only take days for robust optimization.  However the S-100 68K V3 CPU board has been redesigned multiple times and has been in trace route optimization for more than two years.


Trace route optimization is a different process than hand routing or autorouting the PCB traces.  Optimization starts with a completed PCB trace route and seeks new alternative routes to shorten overall trace length and the number of vias.  I can usually get an unoptimized PCB trace routed by hand or by autorouter in a day or so. 


The problem with unoptimized PCB trace layouts, even manual ones, is they generate some very long and complex trace lengths that can screw up timing.  Trying to debug an unoptimized PCB layout is much more difficult since it is so hard to separate logical problems from trace related anomalies.  I usually do a mix of manual and autorouted PCB trace layouts.


As a related side issue, there is a major limitation IMO to free/open source hobbyist PCB design because FreeRouting.net is free to use but not Free/Open Source software.  Without a PCB autorouter we are left with only manual PCB routing and manual optimization.  There have been multiple requests to the FreeRouting.net author to open up his code but due to pre-existing commercial licensing relationships that is just not possible.  That’s not a criticism of FreeRouting.net and I appreciate all they’ve done but it is still a huge issue for hobbyist PCB design projects.


If you or anyone else is interested in helping the hobbyist PCB design community, please consider contributing effort to the QAutorouter project.  It is porting the gEDA autorouter code into a standalone tool set builders can use to manually trace route, autoroute, and optimize PCB traces.  Mike Sharkey (on this list) is the main author.  Strategically, this is the most important hobbyist project any builder could be working on since it lays the foundation for a completely free/open source EDA toolset which would benefit *all* projects.  This is a pure software development issue and a great opportunity to make a lasting contribution.




Thanks and have a nice day!

Andrew Lynch


From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Bill Dromgoole
Sent: Sunday, February 24, 2013 2:21 PM
To: n8vem...@googlegroups.com
Subject: Re: [N8VEM-S100:1465] S-100 board reorders


I have a slightly off topic question for you.

I have never made a PC board or trace routed or optimized a board.

Could you explain the process?

How do you start with chip placement? What software do you use? Is this a professional version or is it something a hobbyist could get freely. What kind of computer is the board designed on, is it vintage?

How long does optimization take to complete? It seems like it takes weeks or months to complete. Is this run on a modern computer? Is optimization different that trace routing or is it just the final step of the process?


I know that's a lot of questions but you did ask "Questions?".

Thanks for all your work.




----- Original Message -----

Sent: Sunday, February 24, 2013 12:17 PM

Subject: [N8VEM-S100:1455] S-100 board reorders



Well I was hoping to get the S-100 68K and S-100 80286 CPU board PCBs ordered next but they are not cooperating.  The S-100 68K CPU board is nearly complete and should be done soon.  It has taken much longer than I expected though.  I would like it to complete trace route optimization before ordering PCBs.

In the meantime, I am thinking we could make another round of S-100 board reorders.  What I am thinking is the S-100 IDE V2 PCBs are always popular and so are the S-100 buffered prototyping board PCBs.  I would like to do another round of those and hopefully while they are settling the S-100 68K CPU and the S-100 80286 CPU boards will complete or at least get “close enough”


Another idea is the S-100 bus terminator board.  Basically there are 10 builders willing to get these boards “as is” which is the full sized PCB with some prototyping area.  Nothing fancy but useful for terminating a legacy S-100 backplane.  However these have *NOT* been prototyped so there is some additional risk.  I think it is minor though since the S-100 backplane has this exact circuit and it works fine.


Ideas?  Thoughts?  Comments?  Questions?  All welcome!  Please lets discuss what the next steps should be.  Thanks and have a nice day!

Andrew Lynch

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