Modules

Some basic information of modules

Modules contain instance of other modules, which forms a hierarchy.

When connecting modules, only the ports on the module are important. You do not need to know the code inside the module.

The code for module mod_a looks like this:

module mod_a ( input in1, input in2, output out );
    // Module body
endmodule

The hierarchy of modules is created by instantiating one module inside another, as long as all of the modules used belong to the same project (so the compiler knows where to find the module). The code for one module is not written inside another module's body (Code for different modules are not nested).

You may connect signals to the module by port name or port position.

Connecting Signals to Module Ports

There are two commonly-used methods to connect a wire to a port: by position or by name.

By position

The syntax to connect wires to ports by position should be familiar, as it uses a C-like syntax. When instantiating a module, ports are connected left to right according to the module's declaration. For example:

mod_a instance1 ( wa, wb, wc );

This instantiates a module of type mod_a and gives it an instance name of "instance1", then connects signal wa (outside the new module) to the first port (in1) of the new module, wb to the second port (in2), and wc to the third port (out). One drawback of this syntax is that if the module's port list changes, all instantiations of the module will also need to be found and changed to match the new module.

• By position时，需要关注端口的顺序

By name

Connecting signals to a module's ports by name allows wires to remain correctly connected even if the port list changes. This syntax is more verbose, however.

mod_a instance2 ( .out(wc), .in1(wa), .in2(wb) );

The above line instantiates a module of type mod_a named "instance2", then connects signal wa (outside the module) to the port named in1, wb to the port named in2, and wc to the port named out. Notice how the ordering of ports is irrelevant here because the connection will be made to the correct name, regardless of its position in the sub-module's port list. Also notice the period immediately(句点) preceding the port name in this syntax.

Problem statement

Connect the signals.

module top_module ( input a, input b, output out );

endmodule

Solution

module top_module ( input a, input b, output out );
    mod_a inst (a,b,out);   // By position
    // mod_a inst (.in1(a), .in2(b), .out(out));        By name
endmodule