Experimental Physics and
Industrial Control System

[email protected] (Jeff Hill) · Fri, 16 Feb 96 15:23:05 MST

Andy,

> We are using AR to store a large number of waveforms.  The database records define
> the array type (FTVL) as either USHORT or UCHAR.  However, AR converts these to
> type `float' on output to the archive files.  

The unsigned integer types used internally in the database do not currently exist 
in the ca client API. To get around this problem EPICS ioc core informs clients attached to
"unsigned int" fields that the native type is "float". This promotion to a larger
type guards against the loss of information during type conversions.

Johnny Tang at CEBAF has recommended that "unsigned char" and "unsigned short"
should map to a 32 bit integer external type (without loss of information). This 
change is planned for the next release of EPICS.

> On a related subject--I noticed that db_access.h and dbFldTypes.h (in base/include) 
> define the "DBF_" types differently.  After browsing through the base and extensions 
> source code, I found some code includes db_access.h whereas some code includes 
> dbAccess.h, which in turn includes dbFldTypes.h.  Which is correct?

The db/rec/dev support use dbAccess.h and the ca clients use db_access.h. EPICS
guarantees that all release 3.xx clients can communicate with any release 3.xx server.
Sending a new and unexpected type code to an old client would violate this guarantee.
Therefore we are waiting for release 4.xx of EPICS to fix this problem.

Jeff

______________________________________________________________________
Jeffrey O. Hill			Internet	[email protected]
LANL MS H820			Voice		505 665 1831
Los Alamos, NM 87545 USA 	FAX		505 665 5107

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System