[HECnet] TOPS-10 D-Day, DECnet failure on November 9th is less than six days away --> 10-nov-2021

[Thomas DeBellis]

Is that KDP link something that is on the 2020, then?  We only had KL's, 
so anything like that would have gone through a DN20.

I am not wholly surprised that VENTI:: needed a reboot; recall that we 
are clamping the value in T1 to 65,535 Julian half-days, so anything 
that is playing with that or otherwise paying attention is going to see 
a monotonically increasing value that got pretty large wrap around to 
something close to the smallest possible value (maybe even zero).

For the seconds remainder in T2, if this goes negative, then the same 
thing will happen (a clamp to 1 second), but since that is only 
monotonic by day, this shouldn't matter.

However, the code ignores T3 (the number of milliseconds), but if T2 
goes negative, then so will T3. This suggests that T3 needs to be 
clamped, as well.  The following code is a potential fix:

    At label NMXTIM + 9 lines, (Decimal) change

             IDIVI T3,JIFSEC         ;CONVERT TO NUMBER OF MILLISECONDS.

             SKIPL T2                ;MAKE SURE WE HAVE A POSITIVE
    NUMBER OF SECONDS

             TDNE T1,[XWD -1,600000] ;MAKE SURE NO DATE OVERFLOW

      To:

             IDIVI T3,JIFSEC         ;CONVERT TO NUMBER OF MILLISECONDS.

             MOVMS T3                ;Ensure milliseconds are always
    positive

             MOVMS T2                ;Ensure seconds are always positive

             TDZA T1,[XWD -1,600000] ;Ensure no Julian half day overflow

The assumption here is still that the result in T1, T2 and T3 is only 
being used for logging which may not be correct.
> ------------------------------------------------------------------------
> On 11/9/21 9:03 PM, Robert Armstrong wrote:
>
> >VENTI:: is offline, so I hope our patch didn't take it out of 
> commission...
>
> Well that’s interesting.  The system is still running, but the KDP 
> link has dropped for some unexplained reason.  There are no STOPCODEs 
> nor any other error message on the console; just a steady stream of 
> hourly status reports going back a couple of days.
>
> I rebooted it and the KDP link came up immediately, and DECnet appears 
> to be working again.
>
>   Don’t know.  There may be some other glitch that occurs when the 
> time rolls over.
>
> Bob
>
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