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authorYann Herklotz <ymh15@ic.ac.uk>2020-11-21 00:03:19 +0000
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This section describes the Verilog semantics that was chosen for the target language, including the changes that were made to the semantics to make it a suitable HLS target. The Verilog standard is quite large~\cite{06_ieee_stand_veril_hardw_descr_languag,05_ieee_stand_veril_regis_trans_level_synth}, but the syntax and semantics can be reduced to a small subset that \vericert{} needs to target.
The Verilog semantics we use is ported to Coq from a semantics written in HOL4 by \citet{loow19_proof_trans_veril_devel_hol} and used to prove the translation from HOL4 to Verilog~\cite{loow19_verif_compil_verif_proces}. % which was used to create a formal translation from a logic representation encoded in the HOL4~\cite{slind08_brief_overv_hol4} theorem prover into an equivalent Verilog design.
-This semantics is quite practical as it is restricted to a small subset of Verilog, which can nonetheless be used to model all hardware constructs one would want to use. \JP{``can nonetheless be used to model the hardware constructs required for HLS.''} The main features that are excluded are continuous assignment and combinational \alwaysblock{}s; these are modelled in other semantics such as that by~\citet{meredith10_veril}. %however, these are not necessarily needed, but require more complicated event queues and execution model.
+This semantics is quite practical as it is restricted to a small subset of Verilog, which can nonetheless be used to model the hardware constructs required for HLS. The main features that are excluded are continuous assignment and combinational \alwaysblock{}s; these are modelled in other semantics such as that by~\citet{meredith10_veril}. %however, these are not necessarily needed, but require more complicated event queues and execution model.
The semantics of Verilog differs from regular programming languages, as it is used to describe hardware directly, which is inherently parallel, rather than an algorithm, which is usually sequential. The main construct in Verilog is the \alwaysblock{}.
A module can contain multiple \alwaysblock{}s, all of which run in parallel. These \alwaysblock{}s further contain statements such as if-statements or assignments to variables. We support only \emph{synchronous} logic, which means that the \alwaysblock{} is triggered on (and only on) the rising edge of a clock signal.