More PDP 11 hacking (help!)

From: Vintage Computer Festival <>
Date: Tue Feb 8 13:06:05 2005

On Tue, 8 Feb 2005, Pete Turnbull wrote:

> > But now are new woes: when I type in "DY" to boot off the DY drive
> the
> > system pauses for a split second and then dumps into ODT with 165426.
> > Looking at that address shows that there's no code there.
> No code, as in ODT gives an error (prints a "?" and a carriage return)
> or it's zeros?

No code as in the memory contents are the default at power up (alternating
between 0 and 177777, I think(.

> > However, one thing I noticed is that now, location 0 now has code!
> Yah!
> > Or at least, something is there. If I clear the first dozen or so
> words
> > and then reboot, the zeroes are overwritten. The weird thing is that
> I
> > don't see the drive light going on or the head relay engaging.
> Apart from the lack of drive activity (LED flash and the clunk from
> head relay) it sounds like you haven't got a bootable disk. Or that
> you have, but it's for a different controller (a DX-bootable disk will
> not boot on a DY, nor vice-versa).

I considered that. I'll hopefully be getting a known good RT11 "DY" boot
disk tonight.

> > I've tried the system with both the DSD and RXV21 controllers with
> two
> > different sets of drives and I basically get the same results.
> > No matter whether I boot with DY or DY0 or DY1, it always breaks into
> > at 165426.
> 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. Did you know that you can
> type "P" instead of "G" to make the processor restart at the last-used
> address, without resetting the bus and devices on it, and that you can
> do this with the HALT switch on, so it single-steps? So if enter a
> manual bootstrap at 1000, set the HALT switch, type "1000G" and then
> keep typing "P" you'll single-step through the code starting at 1000.

Yes, I was aware of that but I'm not sure how useful it would be to me at
this point since I'm not versed (yet) in PDP 11 machine lagnuage and
wouldn't know what I should be looking for.

Sellam Ismail                                        Vintage Computer Festival
International Man of Intrigue and Danger      
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Received on Tue Feb 08 2005 - 13:06:05 GMT

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