Messages in this thread | | | Date | Wed, 30 Mar 2005 11:47:18 -0500 (EST) | From | linux-os <> | Subject | Re: How to debug kernel before there is no printk mechanism? |
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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!
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