Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!mcsun!unido!fauern!fauern!csbrod
From: csbrod@medusa.informatik.uni-erlangen.de (Claus Brod )
Newsgroups: comp.sys.atari.st
Subject: Re: STE investigation/ docs discussion [large!]
Keywords: Atari, STE
Message-ID: <2708@medusa.informatik.uni-erlangen.de>
Date: 7 May 90 15:50:19 GMT
References: <20.Apr.90.15:37:24.A100D0@UK.AC.SALF.D> <1990Apr25.135925.22367@newcastle.ac.uk> <2178@atari.UUCP> <37990@brunix.UUCP> <2180@atari.UUCP> <4119@infmx.UUCP> <43725@iuvax.cs.indiana.edu> <1990May2.113400.1884@newcastle.ac.uk>
Organization: CSD, University of Erlangen, W-Germany
Lines: 28

J.Derrick@newcastle.ac.uk (J. Derrick) writes:

>The BIOS and XBIOS trap handlers appear much the same as before, but there seems
>to be an extra XBIOS call $40. This seems to look at $FF8A00, and check for a
>bus error. Its purpose is unknown.

XBIOS(64) has been there since TOS 1.2 and is used to detect the blitter status and turn it on or off. It has been documented officially. Looking at $FF8A00
in a non-blitter ST causes a bus error, while a ST with the blitter installed
doesn't mind. This way, you can detect the blitter chip.

>Going through the initialsation stuff, the code is also mostly as before.
>Memory clearence is now faster, with a few extra writes in the loop. To support
>the new hardware, code has been added, notably around $E002C4. The DMA sound is
>initialised [$FF8900] and the tone control acessed via the microwire bus
>[$FF8922,4]. There seem to be a number of new system variables, for instanve
>look at $980 onwards. These locations come complete with text names: _VDO,
>_MCH, SND, _SWI. _SND is set up according to $FF9200, which after a bit of
>experimentation turned out to be the new joystick ports. Again this is for
>information only- their pupose is unknown.

The things you found at $980 onwards aren't new system variables. ATARI
calls it the 'cookie jar', and it is used by TOS and programs to notify
other programs that they were there and they have done something to the
system. All cookies starting with _ are reserved for ATARI, and they
use them to publish machine data to other programs (CPU type, shifter
type etc.).

Claus Brod