[Simh] Simh Digest, Vol 35, Issue 12

Galen Tackett gtackett at yahoo.com
Fri Oct 20 18:26:30 EDT 2006


Mark Pizzolato wrote:

> The best you can do is to try hard to get the clock stuff "right",
> but since most folks will be running on non-dedicated hardware, there
> will always be quite variable drift.  The same problem exists in the
> various PC emulation/Virtual environments today.  MS Virtual PC, and
> MS Virtual Server, and VMWare all have special "software" packages
> that you install in the simulated computer's OS which talk to the
> simulator directly to facilitate proper time keeping, mouse tracking,
> etc.  Anternatively, I've run a standard NTP based cron job which
> syncs the simulated system's clock to an outside source every 10
> minutes.
>
How about a simh pseudo-device of some kind from which could be read 
the host system's time in some [simh-]standardized format? At first 
guess it doesn't seem like it would need to do much else. Then someone 
could write whatever bit of code the hosted OS would need to read that 
and do whatever to sync the clock. On systems with NTP or something of 
that sort (DECnet-Plus's DECdts comes to mind) this could conceivably 
be integrated with the time synchronization mechanism these provide.

VMS is my hosted OS. I've forgotten far too much about VMS privileged 
code to volunteer to take on a driver or other privileged code--it's 
been a good 15 years or more since I coded at that level on VMS. But I 
have some C code, based on the sample provided with DECdts, that could 
probably be modified to implement a DECdts time provider, once the 
driver was taken care of.

Somehow I suspect that running DECnet-Plus on a simulated VAX, hosted 
on a 433 MHz PowerMac G4, might not be too pleasant, however...

Galen Tackett




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