RE: ai, soft channel, and breakpoint table

["Allison, Stephanie" <saa@slac.stanford.edu>]

Hi John, 

> Is it possible to use a breakpoint table in an ai record to 
> convert the output 
> of another ai record (without loss of resolution)?
> 
> I have an ai record for which device support retrieves a 
> floating point value 
> from hardware and puts it directly into the VAL field.
> 
> I would like to use a breakpoint table in a second ai record 
> to convert the 
> reading of the first record - which (as I understand it) 
> would require me to use 
>   a "Raw Soft Channel". Will a "Raw Soft Channel" ai record, 
> in reading a value 
> into RVAL, convert it to an integer (with a loss of resolution)?
> 
> Alternatives?

I don't know about using a second ai record.  In my case, I ended up using a subroutine record - perhaps a bit ugly, probably somebody knows something better:

long yourSub(struct subRecord *psub)
{
  /*
   * Inputs:
   *          A = Your input
   *          B = Breakpoint Table Index
   *     C to G = spares
   *       DPVT = Pointer to Breakpoint Table
   * Outputs:
   *          H = Value from the Breakpoint Table
   *          I = Spare
   *          J = Previous Breakpoint Table Index
   *       DPVT = Pointer to Breakpoint Table
   *          K = Spare
   *          L = Last Breakpoint
   *        VAL = Your output
   */
  short lbrk;  /* Last breakpoint */

    if (psub->j != psub->b)
    {
      psub->j = psub->b;
      psub->dpvt = 0;
    }
    lbrk    = psub->l;
    psub->h = psub->a;
    if (cvtRawToEngBpt(&psub->h, (short)psub->j, 0,
                       &psub->dpvt, &lbrk)) return -1;
    psub->l   = lbrk;
    psub->val = psub->h;
  return 0;
}

Stephanie Allison