[Info-vax] Timer resolution for sys$setimr() ?

[Arne Vajhøj]

On 12/4/2024 10:01 AM, Arne Vajhøj wrote:
> On 12/4/2024 8:37 AM, Simon Clubley wrote:
>> What is the actual resolution of timer events queued using the
>> sys$setimr() system service ?
>>
>> NOTE: this is about when the timer becomes eligible to fire, not when
>> it actually does, given that VMS is not a hard RTOS.
>>
>> The base VMS time format is in 100ns units, but I couldn't see anything
>> about the units actually used when firing timer events. Is it the same
>> as the hopeless terminal driver timeouts, or is it 100ns, or is it
>> something in between ?
> 
> IDS VMS Alpha 1.5 (30 years old!) says:
> 
> <quote>
...
> </quote>
> 
> which I read as if that on Alpha then VMS checks for SYS$SETIMR
> AST's to queue every 1 millisecond.
> 
> No guarantees when the AST's will actually run.
> 
> And some things may have changed in newer VMS versions and
> newer hardware.

https://hunter.goatley.com/writing-vms-privileged-code/part-v-timer-queues/

has a lot of details.

But is about the same age as the old IDS.

Arne