UCIR2089DirectionalRecords < P1076

P1076 Web>Vhdl2019CollectedRequirements>InterfaceAndBundleEnhancements>UCIR2089DirectionalRecords (2016-01-21, BrentHahoe) (raw view)EditAttach

---+ IR2089: Directional Records

%TOC%

---++ Description of Problem

For many standard interfaces, for instance a bus, there are input and
signals. Both can be combined into a record type individually, but not
together.  Event though both belong together (e.g. request+address
from master to bus, ack+read_data in reverse direction) , they always
have to be listed separately.  The use of inout for ports is a bad
alternative.

---++ Proposed Resolution

I propose a keyword "reverse" or "backwards" or similar in record
definitions.  If such a record is used in a signal or variable
declaration, it is irrelevant.  However in a port declaration, the
"reversed" record components have the reverse direction.  In the
example it would be:
<sticky><verbatim>
    entity CPU is 
    port(
         bus_master : out Tmybusmaster 
            ...
    );
    
    where Tmybusmaster is declared as 
    
    TYPE Tmybismaster is RECORD
                request : std_logic;
                address : std_logic_vector(31 downto 0);
                ack : BACK std_logic;
                error : BACK std_logic_vector(5 downto 0);       
    END RECORD; 
</verbatim></sticky>

ack and error would be inputs, though they are part of an OUT-record.
The binding in an instantiation is not a problem I think, because we
could as well bind the input and output parts individually.  This is
just "syntactic sugar".

Topic revision: r3 - 2016-01-21 - 11:52:05 - BrentHahoe

P1076