[TUHS] DH11 flaw Was: pre-more pager?

Noel Chiappa jnc at mercury.lcs.mit.edu
Thu Nov 9 07:27:53 AEST 2017


    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


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