19 Sep
2024
19 Sep
'24
12:52 a.m.
Even better were DG Novas with core memory, just turn the machine off,
come back in the morning, turn on the machine, pick up where you left off :)
On 09/18/2024 03:38 PM, ron minnich wrote:
Interesting about the amiga. I'm assuming their
firmware zeros memory
on reset, so you have to do handoff from kernel to kernel, not via a
reset and so on?
What was particularly nice about the V6/PDP-11 case: we were able to
yank reset, which let us cleanly reset/disable devices, because
everything was in memory when we got back. I miss the simplicity of
the old machines.
On Wed, Sep 18, 2024 at 3:07 PM Christian Hopps <chopps(a)chopps.org
<mailto:chopps@chopps.org>> wrote:
We had/have this functionality in the Amiga port of NetBSD.
It is implemented as `/dev/reload` device and you copy a kernel
image to it. In locore.s there's code that copies the kernel image
over top of the running kernel and then restarts. I believe for it
to work nothing below the copy code in locore.s can change :)
Thanks,
Chris.
Phil Budne <phil(a)ultimate.com <mailto:phil@ultimate.com>> writes:
the high
ron minnich wrote:
> But I'm wondering: is Ed's work in 1977 the first "kernel boots
kernel" or
was there
something before?
There was! The PDP-7 UNIX listings contain a program trysys.s
https://github.com/DoctorWkt/pdp7-unix/blob/master/src/sys/trysys.s
that reboots the system by reading a.out into user memory (in 4K of core), then copies it to low memory and
jumping to the entry
point. The name suggests its original intended use was to test
a new
system (kernel).
P.S.
Normal bootable system images seem to have been stored in reserved
tracks of the (fixed head) disk (that are inacessible via system
calls):
https://github.com/DoctorWkt/pdp7-unix/blob/master/src/sys/maksys.s
reads a.out and uses I/O instructions to write it out.
P.P.S.
Accordingly, I put together a "paper tape" for booting the system:
https://github.com/DoctorWkt/pdp7-unix/blob/master/src/other/pbboot.s
P.P.P.S.
The system (kernel) is 3K words, the last 1K of low memory
used for the character table for the vector graphics controller.
The definitions for the table are compiled by
https://github.com/DoctorWkt/pdp7-unix/blob/master/src/cmd/cas.s
from definition file
https://github.com/DoctorWkt/pdp7-unix/blob/master/src/sys/cas.in
(after, ISTR, figuring out the ordering of the listing pages!)
I don't think we ever figured out how the initial character table
is loaded into core. One thing that was missing from the table
was the dispatch array, which I recreated:
https://github.com/DoctorWkt/pdp7-unix/blob/master/src/other/chrtbl.s
The system (kernel) could be built for a "cold start", reloading the
disk (prone to head crashes?) from paper tape? But I don't think
anyone ever reconstructed the procedure for rebuilding a disk
that way.
The disk was two sided, and the running system only used one side:
https://github.com/DoctorWkt/pdp7-unix/blob/master/src/cmd/dsksav.s
https://github.com/DoctorWkt/pdp7-unix/blob/master/src/cmd/dskres.s
appear to be programs to save and restore the filesystem from the
"other" side of the disk.