[TUHS] kernel boots kernel in 1977

[Luther Johnson]

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 at chopps.org
> <mailto:chopps at 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 at ultimate.com <mailto:phil at ultimate.com>> writes:
>
>     > 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
>     the high
>     > 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.
>

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