The purpose of Lola is to statically describe the structure and function of hardware components and of the connections between them. A Lola text is composed ofdeclarations andstatements. It describesdigital electronics hardware on thelogic gate level in the form ofsignal assignments. Signals are combined usingoperators and assigned to other signals. Signals and the respective assignments can be grouped together intodata types. An instance of a type is a hardware component. Types can be composed of instances of other types, thereby supporting ahierarchical design style and they can begeneric, e.g., parametrizable with theword width of a circuit.
All of the concepts mentioned above are demonstrated in the following example of a circuit for adding binary data. First, a fundamental building block (TYPE Cell) is defined, then thisCell is used to declare a cascade of word-width 8, and finally theCells are connected to each other. TheMODULE Adder defined in this example can serve as a building block on a higher level of the design hierarchy.
MODULEAdder;TYPECell;(* Composite Type *)INx,y,ci:BIT;(* input signals *)OUTz,co:BIT;(* output signals *)BEGINz:=x-y-ci;co:=x*y+x*ci+y*ci;ENDCell;CONSTN:=8;INX,Y:[N]BIT;ci:BIT;(* input signals *)OUTZ:[N]BIT;co:BIT;(* output signals *)VARS:[N]Cell;(* composite type instances *)BEGINS.0(X.0,Y.0,ci);(* inputs in cell 0 *)FORi:=1..N-1DOS.i(X.i,Y.i,S[i-1].co);(* inputs in cell i *)END;FORi:=0..N-1DOZ.i:=S.i.z;END;co:=S.7.co;ENDAdder.
Wirth describes Lola from a user's perspective in his bookDigital Circuit Design. A complementary view on the details of the Lola compiler's implementation can be found in Wirth's technical reportLola System Notes. An overview of the whole system of tools for digital design is the technical reportTools for Digital Circuit Design using FPGAs (containing a copy of the report on the language LolaLola: An Object-Oriented Logic Description Language).
