Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Tue, 14 Feb 2012 12:34:20 -0600

Hi Nerses,

On 2012-02-14 Nerses Gevorgyan wrote:
> 
> I'm trying to put into waveform record an array of STRINGs.
> 
> As I understood from waveform code and manual the VAL field is
> a void pointer which should be supplied by user.

Sorry, if that's what the record reference manual says it's wrong.

The prec->val field is never actually used inside the record source code.  
When you the access the VAL field of a waveform record through CA or a 
database link, the data is actually fetched from the prec->bptr field, which 
gets initialized in the first pass of record initialization to a point to a 
buffer that holds NELM values of the type FTVL.  Device support should copy 
its data into this buffer, never modify the prec->bptr field itself.

> For a case of array of STRINGs it could have different organizations. Like:
> 1) elements delimited by NULLes
>      aaa\0bbbbbb\0cc\0...
> 2) each element of array has a fixed length chars and the names then
> padded with NULL-es like below
>      aaa\0\0\0\0\0\0\0bbbbbb\0\0\0\0cc\0\0\0\0\0\0\0\0

When FTVL=STRING the array elements are all MAX_STRING_SIZE=40 characters 
long, thus when NELM=2 the buffer is 80 bytes long and the second string 
element starts at offset 40 into the buffer.

Hope this helps,

- Andrew
-- 
Optimization is the process of taking something that works and
replacing it with something that almost works, but costs less.
-- Roger Needham

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System