Messages in this thread | | | From | Vicente Feito <> | Subject | Re: How to debug kernel before there is no printk mechanism? | Date | Wed, 30 Mar 2005 14:54:41 +0000 |
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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). > Notice : All mail here is now cached for review by Dictator Bush. > 98.36% of all statistics are fiction. > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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