Experimental Physics and
Industrial Control System

Di Maio Franck <[email protected]> · Wed, 15 Feb 2012 16:26:49 +0100

Dear all

Just to share a worry, get corrections if I am wrong & ideas if any.

ITER will run 20+ years or more, so we shall avoid the 2038 limit encountered by time representation that use SIGNED 32 bits integer for seconds (cf. http://en.wikipedia.org/wiki/Unix_time).

My understanding is that while time stamps are signed 32 bits integer (+ a second integer for nanoseconds fraction) it should be OK ....up to 2106 (1970+136y).

But to program a "future time event" via CA beyond 2038, no way to use an integer for seconds (cannot have better than a signed 32 bits integer). So one has to use at least one double.

Many variants are possible. With a mantissa of 52 bits (IEEE-64 floats), one could in theory use seconds fractions up to 20 bits (microseconds) but I expect it is not as simple as that. Anyway, we also need nanoseconds so we'll split the time in 2 parts (ex: base + delay).

The device support use 64 bits for time in nanos and our OS is Linux x86_64 bits so no other limits.

I'll appreciate comments from EPICS freaks having face similar questions.

Cheers,
Franck

Franck Di Maio
CODAC System Designer
CODAC Section

ITER Organization, Building 519/027, CHD, Control System Division
Route de Vinon sur Verdon - 13115 St Paul Lez Durance - France
Phone: +33 4 42 17 64 05

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System