On 13 Sep 2006 at 21:08, David Laight wrote:

> On Wed, Sep 13, 2006 at 05:17:01PM +0100, Peter Hardman wrote:
> > 
> > NetBSD appears to install OK, but when I try to boot (pointing the BIOS
> > to the correct drive with the BIOS boot menu) I get:
> >  
> > NetBSD MBR boot
> > Error no operating system
> 
> That error message is output after the mbr code (ie the code in sector
> 0 of the disk) has read the first sector of the partition (sector 63),
> and discovered that either:
> - the first byte read is a zero
> or
> - the last two bytes aren't 0x55,0xaa
> which usually mean that there isn't any code there.
> 
> Geometry issues are unlikely to be an issue (the BIOS can't be THAT broken!).
> However if 'hexdump -C -n512 -s63b /dev/rwd1d' reports valid code, maybe
> the BIOS is broken!

The cd doesn't have hexdump, and mounting the /usr slice and running from 
there, (or from hexdump on a floppy)  hexdump fails with a syntax error - I guess it 
must need something else beside the executable. I'll look into it later.
> 
> You might find that the mbr_ext bootcode (which always does LBA reads)
> avoids any issued with the bios reading the wrong sector with CHS reads.
> OTOH the mbr code you are using verifies that the geometry reported by
> the bios converts the CHS value to in the mbr entry to the LBA value.
> 
mbr_ext can't find the OS either...

I need to get hexdump working. I'll have to put the IDE drive back tomorrow and 
run hexdump from there. I've not got into that level of detail yet. Its a nifty tool- you 
can read the all the gory details in the mbr (or I could if my brain could dig out it's 
386 machine code reference :)

regards,

Regards,
> 	David
> 
> -- 
> David Laight: david@l8s.co.uk
> 

Peter Hardman
Breeder of Shetland sheep and cattle