Re: Manipulating time in records

[Dirk Zimoch <dirk.zimoch@psi.ch>]

Hi Franck,

If you want to use only one value, you can reach 1e-6 second precision 
with a double (e.g. seconds since 1970 or since 1990 as long as you 
count less than 142 years). Is that enough?

If you really need 1e-9 second precision, there is no way around 64 bit 
precision, e.g. 2 longout records. Don't worry about signed or unsigned 
long. You only need to count to 0x3b9ac9ff nanoseconds and 31 bits for 
the seconds is enough for 68 years. (Well, fusion energy should last for 
longer than 68 years, but that's an issue for later.)

Dirk

Di Maio Franck wrote:
> Dear EPICS advanced
>
> An issue that I guess has been encountered in other labs already.
>
> A typical ITER use case:
>
> "Do A at time T", 
> - T: a setting controllable by PV(s),
> - A: an action implemented by a record triggered by an event occurring at time T.
>
> We are implementing this use case with a module that receives time over PTP, so the time shall be expressed with nano-second resolution.
>
> So we need:
> - one unsigned int32 for seconds
> - one (unsigned or not) int32 for fraction of second expressed as nano-seconds.
> Same as time-stamp (TS), right?
>
> Maybe 2 longout but I am not sure if UINT32 is OK with longout.
> In addition, we'll have "pulse time", with a specific time origin, so maybe also sub or calc records to convert between relative and absolute time.
>
> We'll appreciate advices on the records to be used... Good or bad ideas/experiences welcome.
>
> Thanks in advance!
>
> Franck