12 Mar
2016
12 Mar
'16
12:50 p.m.
On Sat, Mar 12, 2016 at 12:32 PM, Noel Chiappa <jnc at mercury.lcs.mit.edu wrote:
The ISOLTS (Isolated Testing Subsystem) performs CPU diagnostics on
multi-CPU systems.
It dynamically reconfigures Multics to take the one of the CPUs offline and
to reserve a bank of memory in one the SCUs (the memory is still visible to
Multics, but reserved for ISOLTs use). The offline CPU is hung at a 'Delay
until interrupt' instruction. The memory configuration switches are then
set on the offline CPU so that the reserved block of memory appears to that
CPU as a 128K block of memory starting at location 0. ISOSLTS when installs
a bootstrap loader in the reserved memory block, with an entry at the
interrupt handler vector.
ISOLTS sends an interrupt to the offline CPU, the interrupt vector
transfers to the bootstrap loader, which sets a flag in memory indicating
that all of that reconfiguration was done correctly. ISOLTS sees the flag
set, and then starts loading tests into memory and running them by setting
the interrupt vector and interrupting the CPU, and watching memory to see
the test results.
When the tests are done, the CPU configuration switches are set back, the
SCU memory is released, and Multics brings the CPU back online.
I get bloody impressed just watching it on the emulator; doing it in a
production environment must have been spectacular.
-- Charles
Noel
From: Charles
Anthony
The enormous number of configuration switches is
due to the extreme
modularity of the system. ... Each bank could taken out of service
The really amazing thing (considering the vintage) was that that
reconfiguration could be done with the power on, and the system running!
E.g. MIT had a two-CPU three-memory system; at night, they used (while the
system was running!) to take off one of the CPUs and a memory box, bring
them
up as a separate development system, and in the morning, add the 'borrowed'
CPU and memory back onto the main system - without ever shutting the main
system down! People using it at the time could't even tell it had
undergone a
mitosis, and then a merge.