procedure call problem

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Its all a question of scope. Calling a procedure the way you have done, or any code outside a process, implicitly declares a process.

Procedures and functions are supposed to be re-useble, but self contained bits of code.

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But procedure does not behave like equivalent replacement with process. In this example if you replace the procedure with equivalent process then it works with process but not with procedure.

try and replace the procedure with this code:

process(reset,clk)
	 	   
	TYPE state_machine IS (check_empty, clear_rdreq);
        VARIABLE state : state_machine;
    BEGIN
        IF(reset = '1') THEN
            state := check_empty;
            rdreq_signal <= '0';
        ELSIF(clk = '1' AND clk'EVENT) THEN
            CASE state IS
                WHEN check_empty =>
                    IF(empty_signal = '0') THEN
                        rdreq_signal <= '1';
                        state := clear_rdreq;
                    END IF;
                WHEN clear_rdreq =>
                    rdreq_signal <= '0';
                    state := check_empty;
            END CASE;
        END IF;
    END PROCESS;