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Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
8 years ago

Instantiation Errors

Hello,

I'm trying to reference my full adder module inside another module but seem to be getting lost somehow in the referencing. I keep getting the error Checker 'Full_Adder' not found. Instantiation 's' must be of a visible checker.

the code I have is:

always @(posedge clk)

begin

if (reset==1) // reset isn't pressed

begin

if (enable==1) //enable is active

begin

case ({ALU_OP})

2'h0 : D = A & B;

2'h1 : D = A | B;

2'h2 : Full_Adder f(A,B,D,C);

2'h3 : D = A * B;

endcase

end

end

end

endmodule

module Full_adder(a,b,answer,carry_out);

//inputs

input [2:0] a,b;

//outputs

output [2:0] answer;

output carry_out;

//wires

wire carry_out;

wire [2:0] carry;

genvar i;

generate

for(i=0;i<2;i=i+1)

begin: generate_N_bit_Adder

if(i==0)

half_adder f(a[0],b[0],answer[0],carry[0]);

else

full_adder f(a,b,carry[i-1],answer,carry);

end

assign carry_out = carry[2];

endgenerate

endmodule

3 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    8 years ago

    A module is not like a C function, it is like a chip on a circuit board, so it cannot be "called" inside sequential code. You must instantiate it on its own in parallel to your always block, and then use the sequential code to control the signals connected to it.

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    8 years ago

    Hi,

    Take care on suggested point about instantiation. 

    
half_adder f(a,b,answer,carry);
full_adder f(a,b,carry,answer,carry);
full_adder f(a,b,carry,answer,carry);
    etc.

    Best Regards,

    Anand Raj Shankar

    (This message was posted on behalf of Intel Corporation)
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    8 years ago

    Hi,

    The issue is the module names. Verilog is case sensitive. In the module you've used "Full_adder" and in the instantiation you've used "Full_Adder" . The tool will think this "Full_Adder " is another module. Just be careful about the module names.

    Plus as pointed out earlier, instances are not like C functions. Use named instances instead of positional as this will reduce the chances of errors.