From:	"Thorsten Erdmann" <thorsten DOT erdmann AT gmx DOT de>
Newsgroups:	comp.os.msdos.djgpp
Subject:	More CD ROM problems
Date:	Fri, 25 Aug 2000 19:40:36 +0200
Organization:	AddCom AG
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To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp
Reply-To:	djgpp AT delorie DOT com

Hi,

I want to built a standalone MP3 player which should be able to play from
CD.
For start I will use a PC under DOS/DJGPP, but later it will become a small
68000
system. So I need to program the CDROM directly on hardware level (MSCDEX
doesn't seem to recognize CD changes anyway).

So I tried Hale's ATA driver and it works fine - mostly. First but minor
problem
is the ATAPI Identify command 0x81. As I understand it is a ATA-like
command. But I get no response from the drive. Also the ATA/IDE-Identify
command fails. On harddrives it works.

Now the main problem. How can I determine if a media is in the drive and if
a media change occurred. I want to display an open or closed CD-drive icon
on the player's display. So I need a command which requests the tray status
and the media changed status whithout interferring with a currently running
audio play command.

What I find out is, that in case of media change the next command to the
drive returns an error condition. But I don't think that's the right way to
detect a media change. I think the Mode Sense Command is the right way, but
I don't understand the description of that command in the ATAPI
documentation.

Maybe someone has a code snippet of such a routine. Hope you can help me.

Thank you
Thorsten

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