16-bit bootloader support?

16-bit bootloader support?

[Gabe Black]

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So I have a real-time OS named Pharlap that has a 16-bit bootloader that 
ends up switching to 32-bit protected mode and loads the OS.  I think it 
relies on the first sector of the partition being loaded and execution 
simply started - but in real-mode. 

Is there any way to have grub do this (legacy or grub2)?  I tried 
chainloading, but I think that may be loading it in 32-bit mode.  Any 
pointers on what code I would have to modify to create that option for 
grub?

Any help is appreciated.

Thanks,
Gabe Black | National Instruments | System Software | 512.683.8761

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Re: 16-bit bootloader support?

[Felix Zielcke]

Am Mittwoch, den 07.10.2009, 14:26 -0500 schrieb Gabe Black:
> 
> So I have a real-time OS named Pharlap that has a 16-bit bootloader
> that ends up switching to 32-bit protected mode and loads the OS.  I
> think it relies on the first sector of the partition being loaded and
> execution simply started - but in real-mode. 
> 
> Is there any way to have grub do this (legacy or grub2)?  I tried
> chainloading, but I think that may be loading it in 32-bit mode.  Any
> pointers on what code I would have to modify to create that option for
> grub? 
> 
> Any help is appreciated. 
> 

chainloader switches to real mode just before jumping to the loaded
bootsector.
But if that bootloader already loads the OS in 32bit mode then multiboot
may be an option.

-- 
Felix Zielcke
Proud Debian Maintainer and GNU GRUB developer

Re: 16-bit bootloader support?

[Vladimir 'phcoder' Serbinenko]

Gabe Black wrote:
>
> So I have a real-time OS named Pharlap that has a 16-bit bootloader
> that ends up switching to 32-bit protected mode and loads the OS.  I
> think it relies on the first sector of the partition being loaded and
> execution simply started - but in real-mode.
>
Why do you need realmode? Using real mode requires grub2 to use more
code. MAybe booting with multiboot in 32-bit mode would be a better
idea? If you need to do some specific tasks before switching to 32-bit
mode speak about it - adding them to multiboot may be useful.
>Is there any way to have grub do this (legacy or grub2)?  I tried
chainloading, but I think that may be loading it in 32-bit mode.  Any
pointers on what code I would have to modify to >create that option for
grub?
chainloading loads in realmode, even the A20 bug is reenabled if
possible. But I discourage usage of it. Chainloading is as unportable as
you can get.
>
> Any help is appreciated.
>
> Thanks,
> Gabe Black | National Instruments | System Software | 512.683.8761
> ------------------------------------------------------------------------
>
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-- 
Regards
Vladimir 'phcoder' Serbinenko
Personal git repository: http://repo.or.cz/w/grub2/phcoder.git 

Re: 16-bit bootloader support?

[Bogdan]

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Most probably the developers of GRUB will say that this is useless but did anyone think of adding 16-bit protected mode support to the Multiboot specification and to GRUB?

Cheers,
Bogdan



      

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Re: 16-bit bootloader support?

[Vladimir 'phcoder' Serbinenko]

Bogdan wrote:
> Most probably the developers of GRUB will say that this is useless but
> did anyone think of adding 16-bit protected mode support to the
> Multiboot specification and to GRUB?
Which mode do you mean?
protected mode=32-bit mode
You may mean vm8086 mode but it's meant only for compatibility purposes.
As such it's an OS responsibility to set it up when executing legacy code
>
> Cheers,
> Bogdan
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> Grub-devel mailing list
> Grub-devel@gnu.org
> http://lists.gnu.org/mailman/listinfo/grub-devel
>   


-- 
Regards
Vladimir 'phcoder' Serbinenko
Personal git repository: http://repo.or.cz/w/grub2/phcoder.git 

Re: 16-bit bootloader support?

[James Courtier-Dutton]

2009/10/7 Gabe Black <Gabe.Black@ni.com>:
>
> So I have a real-time OS named Pharlap that has a 16-bit bootloader that
> ends up switching to 32-bit protected mode and loads the OS.  I think it
> relies on the first sector of the partition being loaded and execution
> simply started - but in real-mode.
>
> Is there any way to have grub do this (legacy or grub2)?  I tried
> chainloading, but I think that may be loading it in 32-bit mode.  Any
> pointers on what code I would have to modify to create that option for grub?
>
> Any help is appreciated.
>

I don't think grub can work on any CPU below a 80386.
It probably will no work on 8086, 80186 and 80286.

Re: 16-bit bootloader support?

[Bogdan]

Well yes, that's exactly what this discussion was about, wasn't it? :)

Cheers,
Bogdan




----- Original Message ----
From: James Courtier-Dutton <james.dutton@gmail.com>
To: The development of GRUB 2 <grub-devel@gnu.org>
Sent: Fri, October 9, 2009 4:06:45 PM
Subject: Re: 16-bit bootloader support?

2009/10/7 Gabe Black <Gabe.Black@ni.com>:
>
> So I have a real-time OS named Pharlap that has a 16-bit bootloader that
> ends up switching to 32-bit protected mode and loads the OS.  I think it
> relies on the first sector of the partition being loaded and execution
> simply started - but in real-mode.
>
> Is there any way to have grub do this (legacy or grub2)?  I tried
> chainloading, but I think that may be loading it in 32-bit mode.  Any
> pointers on what code I would have to modify to create that option for grub?
>
> Any help is appreciated.
>

I don't think grub can work on any CPU below a 80386.
It probably will no work on 8086, 80186 and 80286.


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