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Fix INC and DEC by specifying if alu is the first one

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If it is not the first, only increment or decrement when carry or
borrow is set.
This commit is contained in:
Max Braungardt
2018-04-26 20:09:04 +02:00
parent fdedf7b657
commit a1bebb977e
2 changed files with 21 additions and 5 deletions
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15
firmware/alu/main.vhd
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@ -5,7 +5,8 @@ use ieee.numeric_std.ALL;
entity main is
generic (
WIDTH: integer := 8
WIDTH: integer := 8;
FIRST: boolean := true
);
port (
func: in std_logic_vector(3 downto 0);
@ -77,13 +78,21 @@ begin
when "1001" => -- INC
x <= accu;
y <= (others => '0');
cin <= '1';
if FIRST then
cin <= '1';
else
cin <= carry_in;
end if;
result <= sum;
carry_out <= cout;
when "1010" => -- DEC
x <= accu;
y <= (others => '1');
cin <= '0';
if FIRST then
cin <= '0';
else
cin <= not carry_in;
end if;
result <= sum;
carry_out <= not cout;
when "1011" => -- ZERO