2 Sep
2021
2 Sep
'21
12:43 a.m.
On Wed, Sep 1, 2021 at 12:07 PM Ron Natalie <ron(a)ronnatalie.com> wrote:
I disagree. TRAP according to the processor handbook
was intended to be
used for what UNIX calls system calls. EMT was the emulator trap used to
simulate other operating systems on the same hardware.
The 1969 PDP-11 Handbook <
http://gordonbell.azurewebsites.net/digital/pdp%2011%20handbook%201969.pdf&…
says on p. 41 (PDF page 49): "[Trap] instructions provide for calls to
emulators, I/O monitors, debugging packages, and user-defined
interpreters", but it does not define "emulators". (The OED has several
citations for this sense of "emulator", but before about 1985 the context
seems to be hardware emulation only.)
Nevertheless, DOS/BATCH-11 (1970-71) already uses EMT as the system call
instruction, and it is clear that TRAP was for user use. At that point,
the only other operating system that could be emulated would be the Paper
Tape Software that I mentioned, which used IOT.
(BTW, RSTS/E's hypervisor would reflect any EMT instruction to the RTS (the
actual or emulated supervisor running in any given process, such as
Basic-Plus, RT-11, RSX-11, or Teco), with the exception of an EMT 377, EMT
377 sequence, which was a syscall to the hypervisor itself.)