On Feb 8 2005, 11:30, Jerome H. Fine wrote:
> >Pete Turnbull wrote:
>
> >Depends on what's at location zero. You could try entering a copy
of
> >the normal RX02 bootstrap code at location 1000 and stepping through
it
> >to see what happens and where it goes wrong.
> While there are published bootstraps which can
> be entered starting at 1000, as far as I know,
> the hardware boot code in and EPROM reads block zero
> of any device into memory starting at address zero.
> After that, the PDP-11 starts execution at location
> zero. Thus any bootstrap entered using ODT starting
> at location 1000 will be different from a bootstrap
> read from the floppy.
I wasn't talking about the bootstrap that's read off the floppy; that's
the second-stage bootstrap. The first stage is what's in the boot ROM,
and it's a version of that which can be entered at 1000 (or 10000 in
the case of at most of the tape boots). It then loads the first block
off the floppy into location zero and clears the PC so it continues by
executing the just-loaded second-stage boot at location zero.
So in other words, Sellam could enter a manual bootstrap which emulates
what the bootstrap on the controller does. The main reasons to do that
are that you can see more easiliy what's happening because third-party
cards often don't have an accessible chunk of code that can be
single-stepped.
--
Pete Peter Turnbull
Network Manager
University of York
Received on Tue Feb 08 2005 - 13:01:37 GMT