Subject: Re: bootstrapping
To: None <firstname.lastname@example.org>
From: Bertram Barth <email@example.com>
Date: 06/09/1995 11:22:18
> You don't happen to know what it would take to get your readrom routines
> to write, would you? I am hoping that changing $33 (read logical block)
> to whatever write logical block is, might do the trick.
Yes, Yes and No! :-)
$32/$33 toggles read/write. But the problem is that these ROM-based
routines are bound to the controller which was used to boot from.
ROM-based VMB initializes some fields in the RPB e.g. controller's
physical address, unit-number, device-type, pointer to controller-
dependent io-routines and some more. Since to ROM-based routines
use the information stored in RPB to access the device, it's only
possible to access devices on exactly this controller.
Thus it's e.g. possible to boot from floppy and write the contents
of the floppy to any device (disk/floppy) attached to the same
controller by toggling read/write and unit-numbers in RPB.
But I found no way to to access devices on a different controller.