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Altera_Forum
Honored Contributor I
1,815 Views

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
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3 Replies
Altera_Forum
Honored Contributor I
378 Views

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
Honored Contributor I
378 Views

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
Honored Contributor I
378 Views

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.
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