Messages in this thread | | | Date | Wed, 30 Mar 2005 13:09:51 -0500 (EST) | From | linux-os <> | Subject | Re: How to debug kernel before there is no printk mechanism? |
| |
On Wed, 30 Mar 2005, Vicente Feito wrote:
> Video memory is at b800:0000, for humans 0x0000b800, not at 0x000b8000 >
Wrong. "real-mode" can use a segment address of b800, that doesn't work in protected mode. A segment address of b800:0000 is never under any conditions 0000b800.
FYI, a real-mode segment is a 16-byte entity, therefore there are many segment:offset combinations that can get you to 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/ >
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/
| |