1 files changed, 124 insertions, 0 deletions
diff --git a/vhdl/mcu.vhd b/vhdl/mcu.vhd
new file mode 100644
index 0000000..e20f4f6
--- /dev/null
+++ b/vhdl/mcu.vhd
@@ -0,0 +1,124 @@
+library ieee;
+use ieee.std_logic_1164.all;
+
+library ieee_proposed;
+use ieee_proposed.std_logic_1164_additions.all;
+
+-- use work.mcu.all;
+
+package mcu is
+
+  type mcu_in is record
+    -- SPI interface
+    bit_in              : std_logic;
+    bit_clk             : std_logic;
+
+    -- Strobed to latch data from SPI buffer to AH, AL and Dout
+    byte_out_clk        : std_logic;
+    -- Store to latch data from D bus to Din
+    byte_in_clk         : std_logic;
+    -- Enable AH and AL, active low
+    a_oe                : std_logic; 
+    -- Enable Dout, active low
+    d_oe                : std_logic; 
+  end record;
+
+  procedure byte_out(
+    signal mcu_in       : out mcu_in;
+    byte                : in std_logic_vector(7 downto 0)
+  );
+
+  procedure byte_in(
+    signal mcu_in       : out mcu_in;
+    signal bit_out      : in std_logic;
+    signal byte         : out std_logic_vector(7 downto 0)
+  );
+
+  procedure write_ram(
+    signal mcu_in       : out mcu_in;
+    signal we           : out std_logic;
+    data                : in std_logic_vector(7 downto 0);
+    address             : in std_logic_vector(15 downto 0)
+  );
+
+  constant tClk         : time :=  100 ns;
+  constant disable      : std_logic := '1';
+  constant enable       : std_logic := '0';
+
+  constant mcu_in_initial : mcu_in := (
+    bit_in => '0',
+    bit_clk => '1',
+    byte_out_clk => '1',
+    byte_in_clk => '1',
+    a_oe => '1',
+    d_oe => '1'
+  );
+
+end mcu;
+
+package body mcu is
+
+  procedure byte_out(
+    signal mcu_in       : out mcu_in;
+    byte                : in std_logic_vector(7 downto 0)) is
+  begin
+    for i in byte'range loop
+      mcu_in.bit_in  <= byte(i);
+      mcu_in.bit_clk <= '0';
+      wait for tClk;
+
+      mcu_in.bit_clk <= '1';
+      wait for tClk;
+    end loop;
+  end;
+
+  procedure byte_in(
+    signal mcu_in       : out mcu_in;
+    signal bit_out      : in std_logic;
+    signal byte         : out std_logic_vector(7 downto 0)) is
+  begin
+    mcu_in.byte_in_clk <= '0';
+    wait for tClk;
+
+    mcu_in.byte_in_clk <= '1';
+    wait for tClk;
+
+    for i in byte'range loop
+      byte(i) <= bit_out;
+      mcu_in.bit_clk <= '0';
+      wait for tClk;
+
+      mcu_in.bit_clk <= '1';
+      wait for tClk;
+    end loop;
+  end;
+
+  procedure write_ram(
+    signal mcu_in       : out mcu_in;
+    signal we           : out std_logic;
+    data                : in std_logic_vector(7 downto 0);
+    address             : in std_logic_vector(15 downto 0)) is
+  begin
+    report "write_ram: " & to_string(data);
+
+    -- TODO: busreq + wait for busack
+    byte_out(mcu_in, data);
+    byte_out(mcu_in, address(7 downto 0));
+    byte_out(mcu_in, address(15 downto 8));
+
+    mcu_in.byte_out_clk <= '0';
+    wait for tClk;
+
+    -- Clock the data out on the A and D busses
+    mcu_in.byte_out_clk <= '1';
+    -- Enable A and D outputs
+    mcu_in.a_oe <= enable;
+    mcu_in.d_oe <= enable;
+    we <= enable;
+
+    wait for tClk;
+
+    we <= disable;
+  end;
+
+end mcu;