Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!spool2.mu.edu!news.cs.indiana.edu!msi.umn.edu!noc.MR.NET!gacvx2.gac.edu!gacvx2.gac.edu!scott From: scott@mcs-server.gac.edu (Scott Hess) Newsgroups: comp.sys.amiga Subject: Re: JR-Comm VT100 emulation Message-ID: Date: 4 Jan 91 01:25:39 GMT References: <600@caslon.cs.arizona.edu> <37397@cup.portal.com><647@faatcrl.UUCP> <37439@cup.portal.com> Organization: Gustavus Adolphus College Lines: 32 Nntp-Posting-Host: mcs-server.gac.edu In-reply-to: thad@cup.portal.com's message of 1 Jan 91 00:04:04 GMTLines: 32 In article <37439@cup.portal.com> thad@cup.portal.com (Thad P Floryan) writes: >What baffles me is why it seems to be so difficult for "emulator" writers to >get it right, especially using an MC680x0-family CPU. A real DEC VT100 has a >dinky 8080A CPU, and the Datamedia DT80 uses an 8085 with only a few 4Kx8 >EPROMs; the Datamedia DT80 is actually a better VT100 than DEC's own VT100! >About 8 years ago (1983) I wrote a 100%-compatible VT100-emulator in assembler >which fit in an 8Kx8 EPROM for an MC6803 CPU; just requires a straightforward >fsm (finite-state-machine; state transition matrix; decision table; whatever) >to parse the ESCape codes, branch off to subroutines, and do the right thing. Actually, the amazing compactness of the original is the reason that many emulators are not that good. When programming the original, they had to cram, so many of the functions have bizarre ramifications when combined with others - it's almost like emulating circuits on a CPU. It's not very easy. It took me months to figure out all of the weirdisms, and now my program passes vttest (excepting double-high/wide - due to speed considerations, though I might just forge ahead in a future release). The program runs on NeXTs, though, so it won't help the original poster :-). Another problem with most emulators is that the author cared little for the emulation - rather, the thrust was towards communications. Thus, the author wrote an emulator which communcates fairly decently, but only emulates what s/he needs. Say the author only uses vi . . . -- scott hess scott@gac.edu Independent NeXT Developer GAC Undergrad "Tried anarchy, once. Found it had too many constraints . . ." "Buy `Sweat 'n wit '2 Live Crew'`, a new weight loss program by Richard Simmons . . ."