RE: Linux boot code

["Hua Zhong" <hzhong@cisco.com>]

How It Works: 
DOS Floppy Disk Boot Sector

http://www.ata-atapi.com/hiwdos.htm#T8

> -----Original Message-----
> From: linux-kernel-owner@vger.kernel.org 
> [mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Koala GNU
> Sent: Tuesday, July 15, 2003 2:18 AM
> To: Riley Williams; linux-kernel
> Subject: Re: Linux boot code
> 
> 
> Hi, Riley,
> 
> thanks for your reply.
> 
> I noticed the native boot code for floppy is not supported 
> any more. In 
> fact in the current code display a message and reboot the 
> machine after 
> the press of a key.
> 
> But I am interested on how the old native boot code worked.
> 
> Do you know if there is a particular reason why the boot 
> sector is moved 
> to 0x9000:0 (excuse me if I repeat the question, but I need 
> help on this)?
> 
> I hope someone else can point me a site where is reported the 
> format of 
> the floppy parameter table at address 0x0:0x78.
> 
> Thanks in advance and excuse me for this other post.
> 
> Riley Williams wrote:
> 
> >Hi.
> >
> > > I am looking at the boot code in bootsect.S and I have some doubt.
> > > I tried to search the answers to my questions on
> > > marc.theaimsgroup.com and on Google but I haven't found them.
> >
> >I know nothing about the former site, so can't comment thereon.
> >
> > > Probably these are newbie question but I'll appreciate if someone
> > > of you help me.
> >
> >I'll do what I can.
> >
> > > 1) In the bootsect code the first thing that is done is to copy
> > >    the boot sector to 0x90000 and move the program count to
> > >    0x9000, go. Why it is necessary move the code there? Is it not
> > >    possible continue the process from 0x7C00?
> >
> >Following moving the boot code there, the next step is to load the
> >kernel image, either from 0x10000 (64k) or from 1M upwards, this
> >being dependent on various factors. However, the boot sector holds
> >several flags whose values are important AFTER the kernel image has
> >been loaded, so is moved out the way first.
> >
> > > 2) Another step is to move the parameters table from 0x78:0 to
> > >    0x9000:0x4000-12. What are the info contained in this table?
> > >    Can you send me a link to a site that specify these info?
> > >    Without these info I am not able to understand these three
> > >    line of code
> > >
> > >        movb    $36, 0x4(%di)           # patch sector count
> > >        movw    %di, %fs:(%bx)
> > >        movw    %es, %fs:2(%bx)
> >
> >That area of memory contains parameters configured by the BIOS of
> >the machine in question. I would suspect it's the parameters for
> >the floppy drives, and the code that follows is presumably that
> >used to determine how many sectors per track the floppy in /dev/fd0
> >actually has.
> >
> > > Thanks in advance for your help
> >
> >No problem.
> >
> >Best wishes from Riley.
> >---
> > * Nothing as pretty as a smile, nothing as ugly as a frown.
> >
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