Bootstrap Idea

[A.F.R. Bain]

On Fri, 12 Sep 1997, Warren Toomey wrote:

> All,
> 	I had an idea about bootstrapping images into PDP-11s, please shoot
> it down! Ok, I don't know much about the -11 hardware, how hard would it
> be to bootstrap as follows:
> 
> 	hand-toggle in a small bit of code, which
> 	sucks in a bigger bootstrap over a serial line, which
> 	then can pull in a disk image over the serial line & write to disk

Well I've started to use this approach allready and have written most of
the code.  My scenario is that I have an 11/34 with one RK05, and no other
operating systems.  I have access to almost unlimited number of PDP-11
serial cards, and other unix boxes.

The PDP 11 is configured with two serial ports, one the standard serial
console, the other a 9600 baud serial line.  These go to the two serial
ports on my PC running (which incendtally runs linux).  First I send a
program (binary) as console emulator instructions to the PDP on the
console line.  This program is basically a hacked version of 
/mdec/tboot.s (TU10 boot) which provides getc() and putc() and other bits
and bobs.  It reads in from console a number (rather than a file name)
which is the length of the program to load.  This is read in from the
second serial port and loaded into memory.  I then jump to this and start 
going.  

So the procedure is (1) Load tboot.s via console (2) load RKF to format
RK-05 (this works fine) (2) load the copy program whose name escapes me at
the moment, and transfer the tape image to the RK-05.  (3) Boot the RK-05.

This seemed to work, and progress was only interupted by the need to move
the PDP-11 from Cambridge to home!  I have copies of all the programs
which need a little finishing off, but I could let people have copies if
they are interested.  Incidentally I assembled the on Supnik's emulator
and then punched them out to the virtual PTP.

In fact I also have a longish document which goes through the entire
process with all the code (and some new comments) to try and explain how
it all works.

All this was done using V5 unix code btw.

>
 > Flaws:	need different bootstraps for different disks 
> 	need different bootstraps for different serial hardware
> 	how to deal with bad blocks?
> 	very slooow
> 
> Other problems: 5th, 6th Edition came as RK05 images. We could probably
> 	build images for different drives.
> 	7th Edition did a mkfs during installation, but I don't know if
> 	bad blocks were ever dealt with.
> 
> Anyway, this solution would allow a simple program + disk images to be
> put on your nearby PC running Linux/whatever, so no tapes or tape drives
> would be required.

It is slow -- but that doesn't matter if you can go somewhere else while
it happens (as long as your RK-05 doesn't catch fire)

Alan


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