Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!samsung!munnari.oz.au!bruce!cechew
From: cechew@bruce.cs.monash.OZ.AU (Earl Chew)
Newsgroups: comp.os.minix
Subject: Re: Shoelace, Boot sector, Partition sector
Message-ID: <3308@bruce.cs.monash.OZ.AU>
Date: 5 Nov 90 00:04:32 GMT
References: <35159@nigel.ee.udel.edu> <3301@bruce.cs.monash.OZ.AU> <609@escom.com>
Organization: Monash Uni. Computer Science, Australia
Lines: 24

In <609@escom.com> al@escom.com (Al Donaldson) writes:

>Anyway, the convention used by bootsec.s and loader.x is:
>| Before booting the 2nd stage loader:
>| --> set BX = starting cylinder number of partition
>| --> set SI = partition table entry (relative to 0)
>| --> directly set segment registers (DS, ES, SS) to zero
>| --> set up return so 2nd stage starts at CS:AX = 0:7C00

Setting DS=ES=SS:SI to point at the partition table seems like a good idea just
to be on the safe side.

CS:AX = 0:0x7c00 seems unnecessary to me. The code in the boot sector shouldn't
be relying on how it got invoked (except for the parameter passing).

Relying on BX = cylinder number seems strange. Besides, you don't gain much if
the partition starts in the middle of a cylinder. Passing the parameter table
pointer (and drive number) is sufficient.

Earl
-- 
Earl Chew, Dept of Computer Science, Monash University, Australia 3168
EMAIL: cechew@bruce.cs.monash.edu.au PHONE: 03 5655447 FAX: 03 5655146
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