Re: Writing data using channel access link as well as caput, into wavefrom record

[Benjamin Franksen <benjamin.franksen@helmholtz-berlin.de>]

On Wednesday, March 26, 2014 16:06:15 Ganesh Jangir wrote:
>  There are two records t1, t2 in two different ioc on separate linux
> machines. IOC 2
>
>   record(waveform, t2) {
>    field(INP, "t1 CPP")
>    field(NELM, "16000")
>    field(FTVL, "CHAR")
>  }
>
>  IOC 1
>  record(waveform, t1) {
>    field(NELM, "16000")
>    field(FTVL, "CHAR")
>  }
>
>   t2 need to get data from t1, as well as Using caput -S t2 (ONE at a
> time).  [ganesh@01HW183138 ~]$ caput -S t1 abcd
> [...]
>  How to stop t2, from reading value from t1 when some one is doing
> caput -S t2

EPICS doesn't make this easy but it's doable by patching the waveform
record support. Here is a brief outline:

* in the dbd file, make the VAL field special(SPC_MOD).
* add an extra field (say, WRVL, type UCHAR) for internal use so record
  support can remember that someone wrote to the VAL field
* add a special method (if one doesn't exist yet, else add a case for
  VAL to the existing one)
* in this special handling for the VAL field, remember that VAL was
  written (set wrvl=1)
* change the process method so that it reads from INP (via device
  support's read method) only if WRVL is zero, else reset WRVL to zero.

(Others will undoubtedly tell you how to solve your problem w/o changing
the existing record support by adding a number of additional records...)

Cheers
Ben

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