Re: Wrong timestamps in vax test results

BSD uses a bias of (1<<28) for TODR to see if it has a reasonable value, 
otherwise it complains.

-- R

Den 2026-04-11 kl. 17:29, skrev Johnny Billquist:
> Yeah, it's the TODR I was thinking about.
> Possibly 0 if power lost, or not "working", which is a clear 
> indication that time isn't available.
>
> However, if it is non-zero, we don't really know much. It will wrap 
> after approx 497 days. What happens then is unclear. Some machines 
> might stop the counter, others just keep counting. If power have been 
> lost, TODR might be zero, or might just be some low value. VARM 
> recommends that a system sets it to something like a month in, so that 
> it can be obvious if power was lost. However, that is only true if the 
> system as not been powered off more than one year, otherwise, even if 
> that counter is powered the whole time, you have no idea what time it is.
>
> And yes, some machines don't even have a TODR. So this also becomes a 
> question of what machine is emulated. But the majority of all VAXen 
> have a TODR. Ones that don't: uVAX I, uVAX II, 8800, CVAX and VVAX.
>
> But the "preposterous value" is just a subjective value that NetBSD 
> triggers on. There are no "obvious" preposterous values.
>
>   Johnny
>
> On 2026-04-11 15:41, Mouse wrote:
>>> You need to set the clock, using ntp, or a command, or whatever.
>>> VAXen in general do not have an external clock that tells absolute
>>> time.  There is a clock that runs when power is off, but it only
>>> keeps track of time for about a year before it wraps (it's a simple
>>> counter).
>>
>> Don't both of those depend on the particular VAX in question? The one
>> I know best (the KA630) does have a clock chip that keeps absolute
>> time (but with one-second resolution), and I'm fairly sure it doesn't
>> have any "simple counter" clock that runs when power is off - are you
>> talking about the TODR?  It can be subsetted out and even if present
>> may not have battery backup; even if it does, the battery backup often
>> won't last anything like a year (the "year" probably comes from the
>> TODR wraparound time, which is between 497 and 498 days).
>> EL-00032-00-decStd32_Jan90 says
>>
>>        The counter has an optional battery back-up  power supply  
>> sufficient
>>        for  at  least  100 hours of operation, [...]
>>                                         [...].  If the battery has 
>> failed, so
>>        that time is not accurate, then the register is cleared upon 
>> power-up.
>>
>> and also says the MicroVAX-II TODR "Reads as zero, ignores writes".
>> EK-KA630-UG-001 (pages 4-3 and 4-4) agrees, describing the TODR as
>> "read as 0, no operation (NOP) on write".
>>
>> Not that I expect SIMH's KA630 to be popular as a test machine; if
>> nothing else, if the simulation is accurate it's limited to 16M of RAM.
>>
>> /~\ The ASCII                  Mouse
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