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

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
View File

@ -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

11
firmware/alu/tests/toy_16.vhd
View File

@ -11,6 +11,9 @@ architecture test of toy_16 is
constant period: time := 1us;
component main
generic (
FIRST: boolean
);
port (
func: in std_logic_vector(3 downto 0);
accu: in std_logic_vector(7 downto 0);
@ -43,7 +46,9 @@ architecture test of toy_16 is
begin
alu1: main port map (
alu1: main generic map (
FIRST => true
) port map (
func => func,
accu => accu(7 downto 0),
ram => ram(7 downto 0),
@ -52,7 +57,9 @@ begin
carry_out => carry_propagation
);
alu2: main port map (
alu2: main generic map (
FIRST => false
) port map (
func => func,
accu => accu(15 downto 8),
ram => ram(15 downto 8),