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Error: Multiple constant drivers

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Hugo17

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I do have following VHDL code example:

Code: 
	LIBRARY ieee;
	USE ieee.std_logic_1164.all; 

	LIBRARY work;

	ENTITY Test IS 
		PORT
		(	Nios_Reset_n :  IN  STD_LOGIC;
			UserLed :  OUT  STD_LOGIC_VECTOR(4 DOWNTO 0)
		);
	END Test;

	ARCHITECTURE bdf_type OF Test IS 


	COMPONENT misc
		PORT( reset_reset_n : IN STD_LOGIC;
			 userleds_external_connection_export : OUT STD_LOGIC_VECTOR(4 DOWNTO 0)
		);
	END COMPONENT;


	BEGIN 

	b2v_M1 : misc
	PORT MAP(	 reset_reset_n => Nios_Reset_n,
			 userleds_external_connection_export => UserLed);

	UserLed(0) <= '0';

	END bdf_type;



After compiling I get following error message: Error (10028): Can't resolve multiple constant drivers for net "UserLed[0]" at Test.vhd(28)



What I figured out is, that the line UserLed(0) <= '0'; gives the problem but I do not fully understand why because I have not used the signal UserLed elsewhere. It looks like an easy 'problem' here...

Thanks in advance!
 

UserLed(0) is used in two places.

Code VHDL - [expand]
1
2
3
4
5

-- first time here as an output...
userleds_external_connection_export => UserLed);  -- e.g. UserLed(4 downto 0)
 
-- second time here with the assignment...
UserLed(0) <= '0';
 

Ok I see the problem. When I introduce a new signal led_int and change the code like this:

Code: 
architecture bdf_type of Test is 
  signal led_int : STD_LOGIC_VECTOR(4 downto 0);

  component misc
    port (
      reset_reset_n                       : IN  STD_LOGIC;
      userleds_external_connection_export : OUT STD_LOGIC_VECTOR(4 DOWNTO 0)
    );
  end component;
begin 
  b2v_M1 : misc
    port map (
      reset_reset_n =>                       Nios_Reset_n,
      userleds_external_connection_export => led_int
    );

  led_int(0) <= '0';
  UserLed <= led_int;
end architecture;


Why do I get the same error message but here with Error (10028): Can't resolve multiple constant drivers for net "led_int[0]" at Test.vhd(11)?
 

its the same problem. You're driving led_int(0) to '0', and also driving it from the misc component.
 

Ok but how can I avoid it?
I simply would like to write a value to the output UserLed. As it is not possible (see first post) I introduced an internal signal but it is the same problem again.
 

You avoid it by not assigning a signal from multiple places. Simple as that.

how about:

Code: 
UserLed(0) <= '0';
UserLed(4 downto 1) <= led_int(4 downto 1);
 
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    Hugo17

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