Help with simple function call
Hi, just started learning functions in VHDL.
Making a simple mux4 function. I cannot seem to figure out what type
of conditional statements are allowed in functions. Trying quite a few
as you can see, but all of them are giving errors.
Any suggestions?
Thanks.
RishiD
Here is the complete code.
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity hw4_mux4 is
Port ( OpSel : in std_logic_vector(1 downto 0);
A : in std_logic_vector(7 downto 0);
B : in std_logic_vector(7 downto 0);
C : in std_logic_vector(7 downto 0);
D : in std_logic_vector(7 downto 0);
E : in std_logic_vector(7 downto 0);
F : in std_logic_vector(7 downto 0);
G : in std_logic_vector(7 downto 0);
H : in std_logic_vector(7 downto 0);
Z : out std_logic_vector(7 downto 0));
end hw4_mux4;
architecture behav of hw4_mux4 is
signal X : std_logic_vector(7 downto 0);
signal Y : std_logic_vector(7 downto 0);
function mux4 (fA, fB, fC, fD : std_logic_vector(7 downto 0); fOpSel :
std_logic_vector(1 downto 0))
return std_logic_vector is
variable result : std_logic_vector(7 downto 0);
begin
 WITH fOpSel SELECT
 result := fA WHEN "00",
 fB WHEN "01",
 fC WHEN "10",
 fD WHEN "11",
 NULL WHEN OTHERS;
result := fA when fOpSel = '00' ELSE
fB when fOpSel = '01' ELSE
fC when fOpSel = '10' ELSE
fD;
 process (OpSel, A, B, C, D)
 begin
 case OpSel is
 when "00" => result := A;
 when "01" => result := B;
 when "10" => result := C;
 when "11" => result := D;
 end case;
 end process;
return result;
end mux4;
begin
X <= mux4(A, B, C, D, OpSel);
Y <= mux4(E, F, G, H, OpSel);
Z <= X  Y;
end behav;
