More PDP 11 hacking (help!)

From: Vintage Computer Festival <>
Date: Tue Feb 8 14:17:48 2005

On Tue, 8 Feb 2005, Pete Turnbull wrote:

> 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.

One of the manuals I pulled off of bitsavers (can't remember what it was
for) has a bootstrap I can type in. I guess I'll try that if it comes to
it so I can single-step through it, but I think my problems are much more
simpler to solve.

I tried booting from many different disks which all purported to be RT-11
system disks. However, I don't know their condition, I don't know if the
labelling is misleading, and I certainly can't tell for sure if they were
single or double density. Some had directories printed out and pasted to
the disk sleeve which indicated they were double density, but I noticed
that they didn't necessarily match what would be on a bootable system

Anyway, will get a chance to play around with it more tonight (maybe).

Sellam Ismail                                        Vintage Computer Festival
International Man of Intrigue and Danger      
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Received on Tue Feb 08 2005 - 14:17:48 GMT

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