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docs/source/yosys_internals/flow/verilog_frontend.rst
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@ -47,9 +47,9 @@ be found in :file:`frontends/verilog/verilog_lexer.l` in the Yosys source tree.
The lexer does little more than identifying all keywords and literals recognised
by the Yosys Verilog frontend.
The lexer keeps track of the current location in the Verilog source code using
some global variables. These variables are used by the constructor of AST nodes
to annotate each node with the source code location it originated from.
The lexer keeps track of the current location in the Verilog source code with
a ``VerilogLexer::out_loc`` and uses it to construct parser-defined
symbol objects.
Finally the lexer identifies and handles special comments such as "``// synopsys
translate_off``" and "``// synopsys full_case``". (It is recommended to use
@ -178,21 +178,22 @@ properties:
- | Source code location
| Each ``AST::AstNode`` is automatically annotated with the current source
code location by the ``AST::AstNode`` constructor. It is stored in the
``std::string filename`` and ``int linenum`` member variables.
code location by the ``AST::AstNode`` constructor. The ``location`` type
is a manual reimplementation of the bison-provided location type. This
type is defined at ``frontends/verilog/verilog_location.h``.
The ``AST::AstNode`` constructor can be called with up to two child nodes that
are automatically added to the list of child nodes for the new object. This
The ``AST::AstNode`` constructor can be called with up to 4 child nodes. This
simplifies the creation of AST nodes for simple expressions a bit. For example
the bison code for parsing multiplications:
.. code:: none
:number-lines:
:number-lines:
basic_expr '*' attr basic_expr {
$$ = new AstNode(AST_MUL, $1, $4);
append_attr($$, $3);
} |
basic_expr TOK_ASTER attr basic_expr {
$$ = std::make_unique<AstNode>(AST_MUL, std::move($1), std::move($4));
SET_AST_NODE_LOC($$.get(), @1, @4);
append_attr($$.get(), $3);
} |
The generated AST data structure is then passed directly to the AST frontend
that performs the actual conversion to RTLIL.
@ -204,7 +205,7 @@ tree respectively.
Transforming AST to RTLIL
-------------------------
The AST Frontend converts a set of modules in AST representation to modules in
The AST frontend converts a set of modules in AST representation to modules in
RTLIL representation and adds them to the current design. This is done in two
steps: simplification and RTLIL generation.