Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version P 1.00 3/01/86; site pucc.BITNET
Path: utzoo!watmath!clyde!burl!ulysses!allegra!princeton!puvax2!pucc.BITNET!6101695
From: 6101695@pucc.BITNET (Raymond Chen)
Newsgroups: net.micro.apple
Subject: Re: ROM to RAM
Message-ID: <566@pucc.BITNET>
Date: Sun, 18-May-86 11:28:39 EDT
Article-I.D.: pucc.566
Posted: Sun May 18 11:28:39 1986
Date-Received: Fri, 23-May-86 04:35:06 EDT
References: <203@neoucom.UUCP> <3440@reed.UUCP>
Reply-To: 6101695@pucc.BITNET
Distribution: net
Organization: Princeton University Computing Center
Lines: 66

>  DOS links into BASIC's "charget" routine.
Well, sort of.  DOS actually links into KSW, which is a part of the
system, not BASIC.  This explains how DOS can operate from within
the monitor or from Integer BASIC.  (Integer BASIC does not have a
CHARGET routine.)  KSW is not a subroutine.  KSW is a vector which
resides at $38/$39 (zero page).  It is referenced by KEYIN
($FD0C) which is the "official" way of getting characters from the
keyboard.  DOS doesn't worry too much about KSW.  The only reasons
it bothers to trap input is so that (a) it can act upon DOS commands
typed directly at the keyboard (like CATALOG), (b) it can
feed INPUT statements when you are reading from the disk
(with OPEN file, READ file) and (c) it can feed GETLN (the "official"
line input routine) when you are EXECing a file.
  Actually, most of DOS's work is done by its vector into CSW.
CSW is yet another vector (at $36/$37) which is called by COUT,
the "official" Character OUTput routine.)  It is there that DOS
sniffs for a RETURN followed by Ctrl-D.
 
> The other way to extend function is with the "&" function . . .
I have found the Apple PugetSound Program Library Exchange
(the people who put out Call -APPLE) publication "All About
Applesoft" to be very handy, especially the section on Applesoft
internal entry points.
 
> DOS is very tenacious about giving up control.
> . . .  I've found the best way to take over control from DOS is
>to attack DOS itself.
I recommend the "official" method of installing custom routines:
1. Install your routine as if DOS didn't exist.
2. Call $03EA.
$03EA (DOSCONN) connects DOS to your routine by copying the CSW and
KSW vectors into the DOS table at $AA53/AA54 and $AA55/AA56.
If you want to disconnect DOS completely, just put $FDF0 into CSW
and $FD1B into KSW, and DON'T call DOSCONN.  Warning:  Once DOS
is disconnected, you can't do things like CATALOG and such.  If
you want to reconnect DOS, just call $03EA.  (CALL 1002 from BASIC)
 
>You can use this:
>
>        10 FOR I=13*4096 to 65535
>        20 POKE I,PEEK(I)
>        30 NEXT
>
>to move the ROM version to RAM.
It may work, but it is excruciatingly slow.  My method:
1. Drop into the monitor (CALL -151)
2. C081 C081 (This write-enables the bank-switched RAM, but does
              not read-enable it.  If it were read-enabled, the
              system would hang, since there is nothing there to
              read.)
3. D000<D000.FFFFM (This is the monitor equivalent of the BASIC
                    program.)
4. C083 C083  (This write- and read-enables the RAM.  You can now
               deal with it as you please.)
5. make modifications
6. C080 (This write-protects but read-enables the RAM.  Doing this
         makes your newly-modified RAM look like ROM.)
7. ctrl-c (to return to BASIC, if you haven't clobbered it.)
 
If you really want to know, all you really have to copy is the
range F800.FFFF if you are willing to go without BASIC.
 
Please pardon my verbose Pavlovian response.  I'll try not to do it
again.
 
Raymond Chen (6101695@PUCC)  "Don't look at me.  I'm new here."