Re: More than 16 enumerations mbbi / mbbo

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

On Thursday, July 26, 2012, Hinko Kocevar wrote:
> While developing writing Asyn device driver support for our products
> running on Linux OS, we were faced with the need to support more than 16
> enumeration values that are to be represented using mbbi / mbbo records.
> 
> I'm looking for solutions to this problem. We are trying to stay within
> EPICS base provided record types as much as possible, but we have no
> problems to include additional EPICS extensions to out soft IOC in order
> to gain record support. Last resort would be to provide a new record
> type.

Writing a new record type with, say, 32 choices based on the existing 16-
choices versions wouldn't be hard. The problem is that the result won't be 
very useful because CA (Channel Access) limits the number of choices for 
type DBR_XXX_ENUM to 16 which is hard coded in the protocol (see 
db_access.h). So, for instance, a menu button in an operator panel would not 
see all 32 choices but only the first 16; and so on.

A possible work-around would be to somehow split the choices into smaller 
(related) groups, then provide a 'master' mbbi/o for the choice of the 
group, and separate mbbi/o for chosing inside the groups.

Cheers
Ben

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