Obsolescence and maintenance of FPGAs for CMS

Discussion started on July 2001 CMS HCAL meeting in FNAL and continued by email.

Main issues on FPGAs for CMS-HCAL:

List of proposed rules:

- The FPGA designs should be documented following this template.
   and published on web servers with a long lifetime (CMS and ATLAS require to store documents in EDMS).
- The FPGAs should be configurable from VME.
- Each FPGA design should include a register with a version number (the documentation must explain how to access this register)
- Code and schematics should be well commented, including the desired behaviour of each design module.

Discussion on the approaches for maintenance

1) "museum of old computers and tools": provide legacy maintenance and keep a computer(s) and the software in cold storage until needed.
Pros: simpler and cheaper,
Cons: risks. Known cases about legacy equipment that didn't come back to life and was unfixable.

2) "pull forward" approach: keep ones application current with the latest release.
Pros: possibility to use state-of-the-art tools.
Cons: requires a lot of effort and discipline. Problems: Known cases of a new version of a tool that gave a synthesied output drastically different from the previous version, with the same input HDL code. New tools often do not support old devices.

3) "on demand" (or "do nothing"): run the files through the latest versions when there really is a need for it. When making modifications, it is likely to re-simulate and also have a hardware testbench to verify everything (in approach 2, you probably won't check the results), so it is sure everything went fine. Problem: new tools often do not support old devices.

There is a design style that minimize the risks of re-synthetasing on a new tool (synchronous design, as least as possible dependent on special Cores or LPMs).

Tullio Grassi -  NOV 2001
Return to my HCAL CMS working page


Date: Wed, 20 Aug 2003 18:45:04 GMT
From: Philip Freidin <philip@fliptronics.com>
Newsgroups: comp.arch.fpga
Subject: Re: Legacy 4005 series and current Xilinx ISE offerings?

On Wed, 20 Aug 2003 17:21:37 GMT, "JoeG" <JoeG@nowhere.net> wrote:
>So are we STUCK with maintaining  an OLD machine with OLD Xilinx XACT
>software ?
>BTW I've already asked my rep, distrib, and Xilinx the same question -- they
>all said you need to keep the OLD XACT software and maintain an old
>Workstation -- again NOT acceptable.

While I have no great solution for the old software, I have a pretty
good solution for old operating systems and old systems to run them
on. I use a fine product called VMWare www.vmware.com . With it
and a few spare gigabytes of disk on my current machine, I maintain
over a dozen different legacy systems, each with the OS of choice
for that legacy sw, and an environment that lets it run. I also
use it for project isolation, for testing out new versions of sw
that I don't trust to run on my "real" machine, and for isolation
of packages that may interfere with each other.

Given the current cost of IDE disks at below $1.00 per gigabyte,
I get a complete, safe, encapsulated, archived computer for less
than a few dollars, and no physical space in my office. In total,
I maintain about 20 such legacy/test/isolation computers in a
80 gigabyte partition (about 50 GB used), for the cost of about

Philip Freidin