Robert Millan wrote:
>
>> + .long 0
>> + .long 1024
>> + .long 768
>> + .long 32
>>
>
> Maybe better to use 640x480 instead? Not everyone has a large display.
>
>
It's only a recommended resolution. Bootloader will use a mode it
chooses. Perhaps we should remove recommended mode fields from the spec
altogether or make them somehow optional
>> /* The bits in the required part of flags field we don't support. */
>> -#define MULTIBOOT_UNSUPPORTED 0x0000fffc
>> +#define MULTIBOOT_UNSUPPORTED 0x0000fff8
>>
>
> Shouldn't this be 0xeffc ? (0xfffc & ~0x1000)
>
>
AOUT_KLUDGE field is 0x10000 and not 0x1000
>> === modified file 'doc/multiboot.texi'
>> --- doc/multiboot.texi 2010-01-01 20:02:24 +0000
>> +++ doc/multiboot.texi 2010-01-02 16:58:33 +0000
>> @@ -479,7 +479,8 @@
>> preferred graphics mode. Note that that is only a @emph{recommended}
>> mode by the OS image. If the mode exists, the boot loader should set
>> it, when the user doesn't specify a mode explicitly. Otherwise, the
>> -boot loader should fall back to a similar mode, if available.
>> +boot loader should fall back to a similar mode, if available. Boot loader
>> +may also choose another mode if it sees fit.
>>
>
> I agree with changing this, but the phrases seem to contradict each other. If
> the mode exists, what should bootloader do?
>
> I suggest we remove from "If the mode exists..." untill
> "...if available", leaving your "Boot loader may also..." only.
>
>
Actually they were contradicting because "should" means that loader may
choose not to follow the rule
>> @@ -488,7 +489,9 @@
>> Contains @samp{0} for linear graphics mode or @samp{1} for
>> EGA-standard text mode. Everything else is reserved for future
>> expansion. Note that the boot loader may set a text mode, even if this
>> -field contains @samp{0}.
>> +field contains @samp{0}. If video adapter doesn't support EGA text mode or
>> +bootloader doesn't know how to initialise this mode it may set video
>> +mode even if field contains @samp{1}
>>
>
> If the EGA option is obsolete/useless, I'd just make it:
>
> Reserved for backward compatibility. Always contains @samp{0}.
>
> and schedule it for removal in next major version.
>
>
It is useful. It allows payload to say: "I'm ok with video mode but
prefer text one"
>> 84 | vbe_interface_off |
>> 86 | vbe_interface_len |
>> +-------------------+
>> +88 | framebuffer_addr | (present if flags[12] is set)
>> +96 | framebuffer_pitch |
>> +100 | framebuffer_width |
>> +104 | framebuffer_height|
>> +108 | framebuffer_bpp |
>> +109 | framebuffer_type |
>> +110-115 | color_info |
>>
>
> Perhaps it would be simpler for us to arrange it so that flags 11 and 12
> can't be used at the same time. We could just say that flag 11 is reserved
> and unused, and then put these declarations in the offset that used to be for
> VBE. IIRC there were no possible sections after VBE, so the Framebuffer
> section size wouldn't be constrained by that.
>
> But if you prefer to keep flag 11 operational, I don't object. I would
> probably object to GRUB implementing it though.
>
>
If payload wants to use VBE it will. I think that providing this
informtion saves payload a trip to real mode. So this way we encourage
saner real-mode-free OS design.
Do you think it would be useful to make flag 12 structure describe EGA
text too? I attach new diff for multiboot.texi. If it's approved it
should be simple to implement in grub2 and example kernel-- Regards Vladimir 'φ-coder/phcoder' Serbinenko
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