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SubjectRe: [DOC] Debugging early kernel hangs

> > >However, there's still a huge gap between the last progress() message and
> > >availability of the frame buffer device. The simple console has the
> > >advantage of outputing existing printk messages. (basically, it's a
> > >console using prom_printf).
> >
> > Something I forgot to mention about debugging using screen writes. If
> > the problem is caused by incorrect compiler output then even printk can
> > fail. Not because the C code is wrong but because the generated
> > assembler is wrong. Writing direct to screen memory is as simple as it
> > gets and gives the compiler little or no chance to get it wrong.
> How about the possibility to use architecture specific backends? E.g. my
> little Alpha machine has an 8-bit debugging LED port that would be very suited
> for this. Or you could use a parallel port in a similar manner (for those
> vga-less server machines...). Other machines may have a LED system display
> for displaying HEX-digits.
> So when you use an 8-bit value and display it as 2 hex-digits (ok that would
> be 2 assembler insns instead of one..) this kind of devices could be supported
> equally well.

I like this. LEDs on aralel port are very nice debugging device, and having
hooks in kernel for boot-progress indication would be good.


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