Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Thu, 18 May 2017 11:11:46 -0500

Hi Will,

On 05/17/2017 08:43 AM, [email protected] wrote:
> I am working on synchronising the timestamp on an IOC with a timestamp
> register on an FPGA. I need access to the 32 bit fixed point nanoseconds
> word that makes up the lower half of the EPICS timestamp. Using the
> “Soft Timestamp” I can only get the value as a floating point number
> (using ai) or a string (using stringin).

> Is there a way of getting it in the fixed point format I want? As I
> understand it “Soft Timestamp” only works with ai and stringin records.
> Ideally I’d like support for longin records as well.
> 
> record(ai,"$(SYS)-EVR:EventTimestamp"){
>           field(DTYP,"Soft Timestamp")
>           field(TSEL,"$(SYS)-EVR:Event-14-SP.TIME")
> }
>  
> The record is processed by a forward link from "$(SYS)-EVR:Event-14-SP”

If you aren't too bothered about performance (i.e. this won't be
happening at high speed) then you can get the nanoseconds value from the
timestamop by using the stringin device support with a "%f" conversion
specifier, then fetch the resulting string as an integer (say with a
longin record).

If you need higher performance (i.e. don't want to round-trip through
the string representation), I would use a subroutine record with say the
INPA link pointing to the $(SYS)-EVR:Event-14-SP record and in the
subroutine do something like this:

    epicsTimeStamp tick;

    if (!dbGetTimeStamp(&prec->lnka, &tick)) {
        prec->val = (double) tick.nsec;
        return 0;
    }
    return -1; /* Raise SOFT_ALARM, BRSV */

This will fetch the timestamp from the record that INPA is pointing to
and set the VAL field of the subroutine to the nanoseconds field of that
timestamp.

HTH,

- Andrew

-- 
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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System