Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!cs.utexas.edu!yale!mintaka!olivea!tymix!tardis!jms
From: jms@tardis.Tymnet.COM (Joe Smith)
Newsgroups: comp.sys.amiga.tech
Subject: Re: What's the details of the Boot Proceedure?
Keywords: BootBlock, exec, floppy, disassemble
Message-ID: <1181@tardis.Tymnet.COM>
Date: 14 Aug 90 07:32:07 GMT
References: <1990Jul28.175504.8763@csmil.umich.edu>
Reply-To: jms@tardis.Tymnet.COM (Joe Smith)
Organization: BT Tymnet, San Jose, CA
Lines: 37

In article <1990Jul28.175504.8763@csmil.umich.edu> chymes@fribourg.csmil.umich.edu (Charles Hymes) writes:
>I am trying to figure out what is going on with the boot code of
>several programs, including the standard AmigaDos bootblock.
>I need to know:
> (A) Exactly what byte does the code start running at? The RKM 1.3 says
>	"location 12" but is that in decimal or Hex? Some code seems to
>	alreald have run some stuff before the code at 12, decimal starts.
>	Also, what is in that word after the bootblock checksum?

The RKM also refers to devs/bootblock.h, which says:
	struct BootBlock {
		UBYTE bb_id[4];	   /* 'D','O','S','\0' or 'D','O','S','\1' */
		LONG  bb_chksum;   /* checksum */
		LONG  bb_dosblock; /* reserved for DOS patch */
	}  /* These are bytes 0-11, execution starts with byte 12 (decimal) */

> (B) What do the 68k registers contain when the boot block code is loaded
>	and run? Especially the Address registers, Particulary A6.

A1 points to an I/O request to the trackdisk.device, no other registers are
specified in the RKM.  Because the the code returns, A7 can be assumed to
be a valid stack pointer.  Don't know about A6.

> (C) Where is the bootblock loaded into? The RKM 1.3 manual says that
>	it is arbitrary, but two of the first lines in the boot code on
>	one autobooting disk are:
>		PHA $10?? ( I dont remember these two addresses)
>		PHA $2???

PHA is an opcode for a 6502 processor (Commodore-64), not a 68000 (Amiga).
Looks like you're using the wrong disassembler.  The 68000 does handle
position independent code.
-- 
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