Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!cbatt!cbosgd!ucbvax!decvax!mcnc!gbn
From: gbn@mcnc.UUCP (Gary Nifong)
Newsgroups: net.lsi
Subject: SPICE BUG  (Yes really.)
Message-ID: <1579@alvin.mcnc.UUCP>
Date: Fri, 8-Aug-86 14:28:41 EDT
Article-I.D.: alvin.1579
Posted: Fri Aug  8 14:28:41 1986
Date-Received: Sun, 10-Aug-86 19:46:27 EDT
Distribution: net
Organization: Microelectronics Center of NC; RTP, NC
Lines: 53

*
* This is a clarification of the SPICE 2G6 "bug" reported last week and
* a reply to mark@mips.UUCP.
*

*****************************************************************************

>From: mark@mips.UUCP (Mark G. Johnson)

Summary:
	Tests were performed with UNIX Spice 2G6 to see whether
	the specification of "level=2.0" caused Spice to use the
	MOS model for level 1.  The results were that "level=2.0"
	causes Spice to use MOS model level 2.  No bug was found.


	Perhaps the failure to replicate gbn@mcnc's results arises from
	somebody at Berkeley doing "minor revisions" to the major release
	called Spice 2G6.  My tests were performed on virgin Berkeley source
	code (to the best of my knowledge anyway), using a VAX 11/780 running
	UNIX 4.2 BSD.  This copy of Spice 2G6 prints "spice 2g.6   3/15/83" on
	the top line of every output page.
 

******************************************************************************


	I tested Mark's results on a VAX 11/780 running UNIX 4.2 and
found that his tests are correct. I used version "SPICE 2g.6  3/15/83".
The "level=2.0" bug was not valid! So the bug has not been around
forever, I got excited. 


	HOWEVER, the we are running SPICE on a DEC 8600, and the "bug"
is very real. The "bug" appears on two types of machines used here.

	DEC 8600	4.2BSD UNIX   &   4.3BSD UNIX	
	CONVEX C1	4.2BSD Compatible UNIX


	The problem occurs in SPICE in file "mosfet.f" line 114. Where
integer "LEV" is assign the floating point value "VALUE(LOCM +1)".

(line 114)	LEV = VALUE(LOCM +1)

	On the 11/780 the value of "VALUE(LOCM +1)" equals "2.0000000000000000"
and the value of "LEV" equals "2". On the DEC 8600 and the Convex C1
the value of "VALUE(LOCM +1)" equals "1.9999999999999999111" and is truncated
to "1" when assigned to "LEV". So, the problem does exist and designers
should beware. I also remember having bugs similar to this when porting
MCNC's simulator to various 68000 based workstations.

	Gary Nifong, MCNC