PDP OS Boot Sequence: WAS Re: RK05/RL02 Boot Sequence

From: Jerome H. Fine <jhfinexgs2_at_compsys.to>
Date: Wed Jul 7 13:59:05 2004

>Paul Koning wrote:

> >>>>> "Megan" == Megan <mbg_at_theworld.com> writes:
> Megan> Typically, for the -11's, the first block (block 0) of the
> Megan> device is loaded at address 0. The DEC bootblock standard
> Megan> calls for the first word to be a 5 (reset) and the second to
> Megan> be a branch to the rest of the code (so that locations 4/6 and
> Megan> 10/12 at a minimum are free for non-existent memory and
> Megan> illegal instruction traps).
> That doesn't match what I learned (or what's in RSTS 10.1). The reset
> in location 0 was an old convention. But when a real boot block
> standard appeared, it said that 0 had to be a NOP, and 2 a branch to
> the setup code. Also, there had to be a "Szeto ID area" just before
> the branch target.

Jerome Fine replies:

This is what I just found for RT-11:

For V01-15 (1973), there is a "JMP addr" instruction at
location zero. The VECTORs at 60, 60 and 100 are
also used. I checked both the DecTape and RK05
device drivers.

By V02.B (1975), there was a "NOP" at location zero
followed by a "BR addr" instruction. The VECTORs
at 60, 64 and 100 are NOT used. This usage is maintained
for ALL subsequent versions of RT-11 running on a PDP-11
using RK05 or RL02 device drivers (when available). I assume
that all other device drives would be the same.

> As a special case, PRO boot devices must have a HALT (0) in word 0 --
> obviously the ROM boot transfers control to 2 and not 0 as on other
> PDP11s.

Starting with V05.03 of RT-11 from 1985 (a few earlier versions
may also support the PRO hardware), I set up a BOOT image
for a PRO device driver by:
COPY/BOOT:DZ dev:RT11FB.SYS dev:
I then checked the boot code in block zero of dev: and found
NO differences at all (except for the code specific for "DZ").
There was a "NOP" in location zero followed by a "BR addr"
instruction. VECTORs 60, 64 and 100 were all zeros.

Somewhere (very buried, but might be found if it was essential),
I have a bootable RX50 floppy that I tested on a PRO350 about
5 years (probably longer) ago.

If there are any more questions, please ask.

Sincerely yours,

Jerome Fine
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Received on Wed Jul 07 2004 - 13:59:05 BST

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