[Simh] Adding Codar Q-Timer device to PDP-11 SIMH

[Mark Pizzolato - Info Comm]

On Saturday, April 11, 2015 at 10:45 PM, Alan Frisbie wrote:
> I just booted an RSX system image on SIMH and discovered a
> problem with missing hardware.   My physical PDP-11 system has a
> Codar Q-Timer calendar/clock board.   There is a privileged task
> which reads the date & time and sets it in RSX.   An RT-11
> version also exists.
> 
> What I would like to do is write a SIMH device which emulates
> this board, but uses the host system date & time.   It seems
> pretty easy, but I want to know if anyone has already done something like
> this.

Well, there are other simulators which have time of year clocks that do 'something like' this.  The VAX780 TODR has behavior similar to this and it is implemented in vax780_stddev.c.  The MicroVAX2 has a watch chip which has behavior similar to this and is implemented in vax_watch.c.

Meanwhile, your device is a little strange since there doesn't seem to be a documented register interface to program it.  The programming examples in the documentation at: http://www.bitsavers.org/pdf/codar/Q-Timer_Users_Manual_May84.pdf seem to call a routine in ROM provided on the board to actually interface with the hardware clock.

- Mark