Re: How to debug kernel before there is no printk mechanism?

[Vicente Feito <vicente.feito@gmail.com>]

Video memory is at b800:0000, for humans 0x0000b800, not at 0x000b8000


On Wednesday 30 March 2005 04:47 pm, linux-os wrote:
> On Wed, 30 Mar 2005, krishna wrote:
> > Hi all,
> >
> > How can one debug kernel before there is no printk mechanism in kernel.
> >
> > Regards,
> > Krishna Chaitanya
>
> Write directly to screen memory at 0x000b8000, or write to the
> RS-232C UART while polling the TX buf empty bit, or just write
> bits that mean something to you out the printer port.
>
> Screen - memory is 16-bit words with the high-word being
> an attibute byte. FYI 0x07 is a good B&W byte. You can
> initialize a pointer to it as:
>
> unsigned short *screen = 0xc00b8000; Since low memory
> is always mapped, the above cheat will work. The 0xc0000000
> is PAGE_OFFSET.
>
> An early '486 was brought up into a 32-bit protected-mode
> (non linux) operating system using these debugging methods.
> The first time I got to see some symbol written to the
> screen in protected-mode marked the start of a week-end-
> long party. Have fun!
>
> Cheers,
> Dick Johnson
> Penguin : Linux version 2.6.11 on an i686 machine (5537.79 BogoMips).
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