[clug] Rescuing old motherboards the hard way

Paul Wayper paulway at mabula.net
Thu Jun 24 06:18:42 MDT 2010

Hash: SHA1

On 06/24/2010 05:05 PM, Daniel Pittman wrote:
> Can you attach a VGA output, or a regular or USB keyboard for input?  That
> might be more robust than trying to talk over the usually insanely quirky
> serial console support. :/

Haven't tried the USB keyboard, but the VGA output is actually unsoldered
jumpers and unpopulated chip fanouts on the board.  So I don't think I'll be
getting actual display from it.  A pity, as having to put up with the Phoenix
BIOS's emulation of a screen display over 9600 baud terminal is painful.

> That should be pretty much the last stage of BIOS before it does hand-over to
> the boot loader, so ... maybe it doesn't like your boot loader?

That's the theory.

> Er, and make sure you have a partition flagged as bootable, since some BIOS
> implementations hate not having one.  Maybe even try pretending it is an MSDOS
> partition of some sort in the BIOS type flag?

I took one of the disks, put it in a different machine, installed Linux on it,
and then put the disk back where it came from.  No boot.

> Failing anything else, extract the MBR from the original image, disassemble
> it, and see what the heck it is doing differently?  They code at that level is
> pretty much straight forward.  You can even inject little BIOS interactions
> easily enough if you want to try and debug it printf style.

It's been long enough since I have hacked 8086 assembler that I don't really
look forward to the prospect.  And this is somewhat of a low priority.

> I have had a few implementations that recognize ESC-A for control-A in the
> serial console ... and more than a few controller extension BIOS
> implementations that bypass the BIOS bits that the serial console hooks, look
> directly at hardware, and just don't work with the serial console at all.

Definitely an indication that plugging a USB keyboard in might help.

Have fun,

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