Re: [DOC] Debugging early kernel hangs

From: Thorsten Kranzkowski (th@Marvin.DL8BCU.ampr.org)
Date: Sat Sep 23 2000 - 09:02:38 EDT

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    On Sat, Sep 23, 2000 at 09:57:38PM +1100, Keith Owens wrote:
    > On Sat, 23 Sep 2000 12:42:13 +0200,
    > Benjamin Herrenschmidt <bh40@calva.net> wrote:
    > >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.

    my 0.02 EUR
    Thorsten

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    | Thorsten Kranzkowski        Internet: dl8bcu@gmx.net                        |
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