Re: problem about Channel Archiver

[Andrew Johnson <anj@aps.anl.gov>]

Rolf Keitel wrote:
> Doesn't the record processing on an output record call the
> dset->init_record routine during record initialization?
> Isn't it the device support's responsibility to read back an initial
> value from the hardware and stuff it into the rval field?

Yes, there is no read() routine for an output device support; it's the 
device support's init_record() that is responsible for doing the initial 
value readback from the hardware into RVAL if it can, (or into VAL and 
returning 2 instead of 0).

> If you set PINI to YES and the device support does not provide an
> initial rval value, the record is processed after database
> initialization, and would write 0 to the hardware, irrespective of what
> the hardware currently holds?

Unless the record has a constant value set in the DOL field (which does 
not require OMSL=closed_loop), or you have an initHook() to a save-restore 
routine that saved the old VAL before reboot and has already restored it. 
 It also depends whether 0.0 is inside the DRVL/DRVH limits; if not, IVOA 
and IVOV may also control what happens, and the simulation fields too.


However in general, you probably only want to set PINI on an output record 
if the device support can do the hardware value read in init_record(), if 
you have a save-restore initHook() routine, or if the record is in 
closed-loop mode and you can calculate what its initial value should be.

- Andrew
--
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the sunset you made last night.  That was really cool. - Caro