Re: Netboot not detected by system with PCI SCSI host adapter

[Mike Hammer <mike-hammer@usa.net>]

Hello there,

I've rebuilt the netbootrom using the option to *not* search for boot
disks and now Netboot has the chance to boot from the network past
the SCSI boot device.  I guess i would like to clarify my understanding
of INT18H and IN19H once and for all.

>From the documentation that describes these interrupts, it seems INT18H
and INT19H are both sort of used for the same purpose, which is to allow
a bootable device (either bootable disk drive or network adapter with
on-board bootrom) to get boot'ed by the system ROM BIOS.  If Netboot
only uses INT18H then it will *only* get called by the system ROM BIOS
when there's no bootable disk available.  Only time the Netboot's INT18H
will get called is if there's not bootable disk installed in the system.
The odd thing is that my SCSI device was *not* a bootable disk, i.e.
there is no boot partition on it yet (i have not done fdisk and marked
a primary boot partition).  Maybe the SCSI ROM BIOS is posting to the
system of bootable device being present regardless.  

Anyways, by not using INT18H and rather INT19H, Netboot can be not
part of that exclusive chained list of system bootable/bootloader devices.
Thus last one to get chained into this list is the winner and
considered as system bootloader device.

So looks like the system ROM BIOS uses the INT19H first and if it
finds that there's no bootable device in this chain then it will
call down to INT18H.

PS. In regards to my past postings on testing of Netboot 0.9.0d version,
    i could send you two SBC's (Single Board Computer) where one has
    Realtek 8029AS right on the main board and the other having Realtek
    8139A embedded.  If you think this would help in your development and
    work toward future releases, just let me know and i'll FedEx it 
    right to you.  I would need your address though.

    I haven't really had chance to look at Netboot 0.9.0d release
    since i posted couple of the questions which the responses i got from
    the listserv wasn't really helpful in solving the issues.

PSS. Previously i have posted the block0 froma typical Windows 95 (MSDOS7)
     boot floppy.  Is this helpful in adapting mknbi-dos to support
     generating ramdisk from a file as opposed to from floppy?

Regards,

-mh

At 12:48 PM 3/8/99 GMT, you wrote:
>Hello,
>
>Mike Hammer <mike-hammer@usa.net> wrote:
>> Upon booting the sysstem, i can see on the screen that PCI SCSI controller
>> BIOS is displaying its banner message with etc but soon as that's complete,
>> i don't see the Netboot message at all.  As if Netboot has been completely
>> bypassed by either system BIOS or SCSI controller BIOS.
>> [...]
>> So i guess i'm wondering why is that the presence of PCI SCSI adapter
>> BIOS causes Netboot to get not called by the system BIOS?  Or am i seeing
>> a limitation with Netboot in dealing with other add-in adapter BIOS's in
>> the same system?
>
>Do you have a bootable disk connected to the SCSI adapter? If so, and you
>selected interrupt 18h handling during generation of the bootrom the BIOS
>will always load the operating system from the boot disk instead of calling
>netboot. In that case, you have to answer the makerom question "Do you want
>the BIOS to look for boot disks?" with "no", so that interrupt 19h will be
>used. Of course, it's still possible that the SCSI BIOS also redirects
>interrupt 19h after the netboot bootrom has done so. In that case, you
>should place the netboot bootrom on a ROM address higher than the SCSI
>BIOS, so that the bootrom initialization gets called after that of the
>SCSI BIOS and has a chance to redirect the interrupt properly. However,
>if you are using a farily new system with a BBS compliant BIOS I recommend
>to use version 0.9.0d of netboot, as it has full BBS support.
>
>gero.
>
>-- 
>Someone's been mean to you! Tell me who it is, so I can punch him tastefully.
>  - Ralph Bakshi's Mighty Mouse
>--
>Gero Kuhlmann, Hannover     0511/6497525 (Voice)        gero@gkminix.han.de
>===========================================================================
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