View source for Lola (computing)

{{Short description|Hardware description language}}
{{for|the music performance streaming system|LoLa (software)}}
{{Use dmy dates|date=January 2021}}
{{More citations needed|date=March 2025}}
{{Infobox programming language
| name = Lola
| paradigms = [[Multi-paradigm programming language|Multi-paradigm]]: [[Procedural programming|procedural]], [[Imperative programming|imperative]], [[Structured programming|structured]], [[Object-oriented programming|object-oriented]]
| family = [[Niklaus Wirth|Wirth]] [[Oberon (programming language)|Oberon]]
| designers = [[Niklaus Wirth]]
| developer = [[ETH Zurich]]
| released = {{Start date and age|1995|06}}
| typing = [[Static type|Static]], [[Strong and weak typing|strong]]
| scope = [[Scope (computer science)|Lexical]] (static)
| programming language = [[Oberon (programming language)|Oberon]]
| platform = 
| operating system = 
| license = 
| file ext = 
| influenced by = [[ALGOL]], [[Pascal (programming language)|Pascal]], [[Modula]]
| influenced = 
}}
'''Lola''' is a [[hardware description language]] for describing [[Synchronous circuit|synchronous]], [[digital circuit]]s. [[Niklaus Wirth]] developed the language to teach digital design on [[field-programmable gate array]]s (FPGAs) to [[computer science]] students while a professor at [[ETH Zurich]].

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 of [[Declaration (computer programming)|declarations]] and [[Statement (computer science)|statements]]. It describes [[digital electronics]] hardware on the [[logic gate]] level in the form of [[Digital signal|signal]] assignments. Signals are combined using [[Operator (computer programming)|operators]] and assigned to other signals. Signals and the respective assignments can be grouped together into [[data type]]s. An instance of a type is a hardware component. Types can be composed of instances of other types, thereby supporting a [[Hierarchy|hierarchical]] design style and they can be [[Generic programming|generic]], e.g., parametrizable with the [[Word (computer architecture)|word]] 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 ({{mono|TYPE Cell}}) is defined, then this {{mono|Cell}} is used to declare a cascade of word-width 8, and finally the {{mono|Cell}}s are connected to each other. The {{mono|MODULE Adder}} defined in this example can serve as a building block on a higher level of the design hierarchy.

<syntaxhighlight lang="cp">
MODULE Adder;

TYPE Cell; (* Composite Type *)
  IN x,y,ci:BIT; (* input signals *)
  OUT z,co:BIT; (* output signals *) 
BEGIN
  z:=x-y-ci;
  co:=x*y+x*ci+y*ci;
END Cell;

CONST N:=8;
IN X,Y:[N]BIT; ci:BIT; (* input signals *)
OUT Z:[N]BIT; co:BIT; (* output signals *)
VAR S:[N]Cell; (* composite type instances *)
BEGIN
  S.0(X.0, Y.0, ci); (* inputs in cell 0 *)
  FOR i:=1..N-1 DO
    S.i(X.i,Y.i,S[i-1].co); (* inputs in cell i *)
  END;
  FOR i:=0..N-1 DO
    Z.i:=S.i.z;
END;
  co:=S.7.co;
END Adder.
</syntaxhighlight>

Wirth describes Lola from a user's perspective in his book [https://web.archive.org/web/20060117175059/http://www.cs.inf.ethz.ch/~wirth/books/DigitalDesign/ ''Digital Circuit Design'']. A complementary view on the details of the Lola compiler's implementation can be found in Wirth's technical report [https://web.archive.org/web/20170706155816/ftp://ftp.inf.ethz.ch/pub/publications/tech-reports/2xx/236.ps.gz ''Lola System Notes'']. An overview of the whole system of tools for digital design is the technical report [https://web.archive.org/web/20170706155226/ftp://ftp.inf.ethz.ch/pub/publications/tech-reports/2xx/215.ps.gz ''Tools for Digital Circuit Design using FPGAs''] (containing a copy of the report on the language Lola ''Lola: An Object-Oriented Logic Description Language'').

== External links ==
*[http://www.cs.inf.ethz.ch/lola/ CAD Tools for Hardware Design] at [[ETH Zürich]], including the [http://www.cs.inf.ethz.ch/projects/lola/lola_lang/ Lola language page]

{{Programmable Logic}}
{{Modula, Oberon}}
{{Wirth}}
{{Prog-lang-stub}}

{{DEFAULTSORT:Lola}}
[[Category:Hardware description languages]]