9 Nov
2017
9 Nov
'17
3:27 a.m.
From: Ron Natalie
We actually still had some real DEC DH's on our
system.
...
At least the DZ doesn't loop on the ready bit like the kernel printf
This reminds me of something I recall reading about John McNamara (designer of
the DH11) admitting that he'd screwed up a bit in the DH design; IIRC it was
that if you set the input silo alarm (interrupt) level to something greater
than 1 character, and someone types one character, and then nothing
else... you never get an input interrupt!
(Which is why some Unix DH driver which sets the silo alarm level > 1 - to get
more efficient processing by reducing the number of interrupts _if possible_ -
has to call a 'input characters ready from the DH' routine in the clock
interrupt code.)
IIRC McNamara said he should have included a timeout, so that if the silo
count was non-zero,and stayed that way for a while, it should have caused
a timeout, and an interrupt.
I was just looking for this, but couldn't find it. I thought it was here:
http://woffordwitch.com/McNamaraDH11.asp
but it doesn't seem to be. Does anyone recall seeing this anywhere, and if so,
where? Web search engines didn't turn anything up, alas...
Noel