Xref: utzoo comp.sys.amiga.emulations:1079 comp.sys.amiga.programmer:4054
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!jarthur!uunet!cbmvax!drysdale
From: drysdale@cbmvax.commodore.com (Scott Drysdale)
Newsgroups: comp.sys.amiga.emulations,comp.sys.amiga.programmer
Subject: Re: MS-DOS emulator for CDTV?
Message-ID: <22031@cbmvax.commodore.com>
Date: 30 May 91 04:25:25 GMT
References: <1239@cbmger.UUCP> <1991May24.021015.27939@news.iastate.edu> <7!Z_4N|@warwick.ac.uk>
Reply-To: drysdale@cbmvax.commodore.com (Scott Drysdale)
Organization: Commodore, West Chester, PA
Lines: 50

In article <7!Z_4N|@warwick.ac.uk> phupp@warwick.ac.uk (S Millington) writes:
>In article <1991May24.021015.27939@news.iastate.edu> xgr39@isuvax.iastate.edu writes:
>
>>   It would be much better to simply modify the Janus software so as to
>>allow Amiga CD-ROM drives to run IBM CD-ROM software when used in conjunction
>>with a BridgeCard.  Allowing an Amiga CD-ROM drive to run MAC CD-ROM
>
>     Get serious. JANUS won't even use the serial port yet!

janus doesn't use the amiga's serial port for two reasons:

	1) the original designers did a silly thing - they decided that
	   software and hardware could share the same interrupt vector
	   for radically different things.  the interrupt they picked
	   was IRQ 3 (software INT 0BH).  that's the COM2: interrupt.
	   imagine the fun when Telix or your favorite PC terminal program
	   grabs the IRQ 3 vector to provide interrupt driven serial i/o.
	   no more janus software (which depends on INT 0BH).

	2) the original designers didn't think very hard when they designed
	   the COM2: emulation hardware in the custom chips (they didn't
	   think very hard when designing the LPT1: emulation either, or
	   the CGA emulation...).  ie, the COM2: emulation hardware does
	   such a poor job that it wasn't worth enabling.

i don't know how pc's deal with CD ROM drives (ie, do they have real
MS-DOS filesystems on them?  is there a special filesystem?  do they
have to fondle the hardware themselves?).  if they did a reasonable
job, it should be possible to intercept the requests from the application
at a suitably high level and direct them to the amiga (much like what
JDISK.SYS does).  the level at which you tap into the connection between
the application and the device should be low enough that you're not
duplicating alot of ms-dos functionality on the amiga side, but high
enough that you're not at the "emulate the hardware registers" level.

>*****************************************************************************
>* Stuart Millington                 * "A Mind Is A Terrible Thing, Remember *
>*  UUCP:...!mcsun!ukc!warwick!phupp * That." - David Bryan, Bon Jovi        *
>* JANET:phupp@uk.ac.warwick.cu      *****************************************
>*    ? :phupp%warwick.ac.uk@nsfnet-relay.ac.uk                              *
>*****************************************************************************

  --Scotty
-- 
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Scott Drysdale           Software Engineer
Commodore Amiga Inc.     UUCP {allegra|burdvax|rutgers|ihnp4}!cbmvax!drysdale
		         PHONE - yes.
"Have you hugged your hog today?"
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