Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Thu, 10 Mar 2016 11:56:26 -0600

Hi Gennaro,

On 03/10/2016 08:29 AM, [email protected] wrote:
> 
> but I cannot give a value to mbbo greater than (2^16)-1
> (e.g. the value of a 32-bit register)

The VAL field of an MBBO record doesn't have to be copied directly to
the raw hardware output, the record type provides a way to use more
bits, see below for details. If you really want direct access to the
output bits though you should consider using a longout record instead,
which I think will also work with Mark's Asyn device support and
asynMask syntax.

The MBBO record can use the VAL field as index to choose one of the xxVL
fields whose value is then sent to the hardware. For example when
mbbo.VAL is 1 (which maps to the choice string from the ONST field), the
hardware gets the value from the ONVL field. If you don't set any of the
xxVL fields though the record just copies the VAL field to the output,
which is probably the behaviour you've been seeing.

As Mark Rivers has explained those xxVL fields are 32 bits wide, so you
can send any combination of bits you like. The only limitation is that
you can usually only specify up to 16 different bit-patterns that can be
used by a single mbbo record since there are only 16 sets of choice
fields, but that is because Channel Access only supports ENUM types with
up to 16 choices. There are ways to extend that but they involve
combining several records.

HTH,

- Andrew

-- 
There are only two hard problems in distributed systems:
  2. Exactly-once delivery
  1. Guaranteed order of messages
  2. Exactly-once delivery
 -- Mathias Verraes

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System