17 Nov
2014
17 Nov
'14
4:14 p.m.
Since I do have a BDV11, am I correct in that I should just leave the aux
switch alone and continue debugging elsewhere?
Thanks!
On Mon, Nov 17, 2014 at 9:35 AM, Noel Chiappa <jnc at mercury.lcs.mit.edu>
wrote:
--
Ben Sinclair
ben at bensinclair.com
From: Ben
Sinclair
I wasn't clear though on the discussion about
the line clock... If my
machine is having problems with the line clock, would I need to do
anything to the aux switch, other than leave it in a certain
position?
Well, I wouldn't call it a 'problem'. The thing is that the 11/03 and 11/23
were, unlike all other PDP-11s, designed with a line clock which _the
software
could not enable/disable_. [*] The only way to turn the LTC on/off on those
machines is with that front-panel switch. When running software which _does
not_ handle line clock interrupts, turning the LTC on will blow the
software
away - it will get an un-handled interrupt. (As happened to you.)
So if you're running code which does not use/handle the LTC (like XXDP,
apparently), turn it off. If you're running something that does want/need
it,
turn it on. (And some software may require that it be _off_ while booting,
and
turned _on_ once the system has started - Unix V6 falls into this
category.)
* Two caveats. First, the 11/23-PLUS _does_ have software control over the
LTC; there's an LTC register on that board; it's only the dual-height 11/23
which does not. Second, the BDV11 card has this really elegant kludge that
basically adds an LTC register to a 11/03 or an 11/23, so on an 11/03 or
11/23
with a BDV11, you can leave the LTC switch on all the time, and the
software
can enable line clock interrupts if it wants them.
Noel