function syntex error in compilation

[maheyadav333]

why this function show the syntex error during compilation ?

# ** Error: C:/Users/user/Desktop/function bilbo/bilbo reg func.vhd(1): near "function": syntax error


function bilbo_reg (Si, b1 ,b2: std_logic;
Z: std_logic_vector(7 downto 0);
Q: std_logic_vector(7 downto 0))

return std_logic_vector is

variable FB: std_logic;
variable mode: std_logic_vector(1 downto 0);

begin

FB <= Q(1) xor Q(2) xor Q(3) xor Q(7) ;

mode := B1 & B2;
case mode is
when "00" => -- Shift register mode
Q <= Si & Q(1 to NBITS-1);
when "01" => -- Pseudo Random Pattern Generator mode
Q <= FB & Q(1 to NBITS-1);
when "10" => -- Normal Operating mode
Q <= Z;
when "11" => -- Multiple Input Signature Register mode
Q <= Z(7 downto 0) xor (FB & Q(7 downto 1));
when others =>
end case;

return Q;

end bilbo_reg;

 

[FvM]

I guess, the function appears in a place, where no function is allowed, outside a package or architecture body, or without correctly finishing the preceeding declaration. In other words, the cause is before the text you're posting.

 

[vipinlal]

You are using variables inside a process. So this line is wrong:
FB <= Q(1) xor Q(2) xor Q(3) xor Q(7) ;

Use ':=' instead of '<=' while assigning to variables.

Change other lines too.

Also I am not sure whether you can return Q or not. I suggest you declare a temp variable and then copy the value of Q to it, in the beginning. And return this temp variable instead of Q.

 

[TrickyDicky]

Also, you cannot assign values to Q. It is an input to the function (and is also a constant). The only output is the return value. Therefor you need to make Q an internal variable rather than function input.