Experimental Physics and
Industrial Control System

Ralph Lange <[email protected]> · Fri, 17 Jun 2005 16:18:03 +0200

Marty Kraimer wrote:

The only place we see that V3 epics records need unsigned is for bit

masks.

However there is a big problem with the mask fields in the the mbbXXX

records.

The mask field is 32 bits. How do we handle a 64 bit I/O module?
OK with V4 we can make the mask fields be 64 bits.
But how do we handle a 128 digital I/O module?
Also a 16 bit digital I/O module has many unused bits.

A way to handle this is to make the mask fields an array of octets.

The byte and bit order must still be decided but at least any multiple

of 8 bits can be handled.

I see your line of argumentation and I do like the idea of handling all

bitfield data as arrays of octets. I guess with that trick we can ship

anything around that doesn't need to be used in calculations.

But what about real unsigned numbers? Like results of an ADC conversion

that maps 0-10V to 0-65535 (not that uncommon)? Do we want to use 32bit

integers in all these cases wasting ~50% of the bandwidth on CA? And

wonder why writing a high number through a 32bit int to a 16bit DAC

yields unpredictable results without the client getting an out-of-range

exception? Transport it as an array of octets and reassembling it to an

integer (unsigned or not) on both ends?

If Java was the only language that didn't use unsigned I would be less

willing to adapt to it. But my impression is that the use of unsigned is

coming from C/C++ and getting less popular in more recent languages.

What will be fashionable in 5 years?

Ralph

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System