HDL Enumerations

If you are like me and have trouble remembering what bits correspond to what setting or action in your code then enumerated types are your best friend.

To create an enumerated type just follow this syntax:

type STATE_TYPE is (IDLE, READ1, READ2, WRITE1, WRITE2);
attribute ENUM_ENCODING: STRING;
attribute ENUM_ENCODING of STATE_TYPE:type is "000 001 010 011 100"; 

This creates a data type called STATE_TYPE that contains the enumerations: IDLE, READ1, READ2, WRITE1, WRITE2

These enumerations use the following encoding respectively: 000, 001, 010, 011, 100

All you have to do to create a signal that uses such an enumerated type is specify STATE_TYPE (or whatever you choose to call it) as the data type in your signal declaration.

Hope this helps.