I am getting a Can't open include file error with yosys. Is there a command line argument to define include directories and/or is there a default directory it is looking for include files in?
Include directories can be passed as arguments to read_verilog:
read_verilog -Ipath/to/includes rtl/main.v
read_verilog -Ipath/to/includes rtl/stuff.v
Alternatively the command verilog_defaults can be used to set options for all subsequent calls to read_verilog. For example:
verilog_defaults -add -Ipath/to/includes
read_verilog rtl/main.v
read_verilog rtl/stuff.v
By default, read_verilog is looking for include files in the current working directory and in the directory that contains the verilog file with the `include statement.
Edit re. the comments:
I have created the following example:
$ cat a.v
`include "b.v"
module test;
initial $display(`message);
endmodule
$ cat b.v
`define message "Hello World!"
I can successfully run this with yosys -p "read_verilog a.v" as well as with yosys a.v. Please edit the question so it includes an example where processing of the include files fails.