SA0161: Unpacked structure in packed structure

Function	Determines unpacked structures that are used in packed structures.
Reason	The compiler normally places an unpacked structure on an address that allows aligned access to all elements within the structure. If you create this structure in a packed structure, aligned access is no longer possible, and access to an element in the unpacked structure can lead to a misalignment exception at runtime.
Importance	High

Sample:

The structure ST_SingleDataRecord is packed but contains instances of the unpacked structures ST_4Byte and ST_9Byte. This results in a SA0161 error message.

{attribute 'pack_mode' := '1'}
TYPE ST_SingleDataRecord :
STRUCT
    st9Byte          : ST_9Byte; // => SA0161 
    st4Byte          : ST_4Byte; // => SA0161 
    n1               : UDINT; 
    n2               : UDINT; 
    n3               : UDINT; 
    n4               : UDINT;
END_STRUCT
END_TYPE

Structure ST_9Byte:

TYPE ST_9Byte :
STRUCT
    nRotorSlots      : USINT;
    nMaxCurrent      : UINT;
    nVelocity        : USINT;
    nAcceleration    : UINT;
    nDeceleration    : UINT;
    nDirectionChange : USINT;
END_STRUCT
END_TYPE

Structure ST_4Byte:

TYPE ST_4Byte :
STRUCT
    fDummy           : REAL;
END_STRUCT
END_TYPE