Subversion Repositories light8080

--------------------------------------------------------------------------------
-- Light8080 simulation test bench.
--------------------------------------------------------------------------------
-- This test bench was built from a generic template. The details on what tests
-- are performed by this test bench can be found in the assembly source for the 
-- 8080 program, in file asm\exer.asm.
-------------------------------------------------------------------------------- 
-- 
-- This test bench provides a simulated CPU system to test programs. This test 
-- bench does not do any assertions or checks, all assertions are left to the 
-- software.
--
-- The simulated environment has 64KB of RAM covering the whole address map.
-- The simulated RAM is initialized with the contents of constant 'obj_code'.
-- This constant's contents are generated from some .HEX object code file using 
-- a helper script. See the perl script 'util\hexconv.pl' and BAT files in the 
-- asm directory.
--
-- This simulated system provides some means to trigger hardware irq from 
-- software, including the specification of the instructions fed to the CPU as 
-- interrupt vectors during inta cycles. This is only meant to test interrupt 
-- response of the CPU.
--
-- We will simulate 8 possible irq sources. The software can trigger any one of 
-- them by writing at ports 0x010 to 0x011. Port 0x010 holds the irq source to 
-- be triggered (0 to 7) and port 0x011 holds the number of clock cycles that 
-- will elapse from the end of the instruction that writes to the register to 
-- the assertion of intr. Port 0x012 holds the number of cycles intr will remain 
-- high. Intr will be asserted for 1 cycle at least, so writing a 0 here is the 
-- same as writing 1.
--
-- When the interrupt is acknowledged and inta is asserted, the test bench reads
-- the value at register 0x010 as the irq source, and feeds an instruction to 
-- the CPU starting from the RAM address 0040h+source*4.
-- That is, address range 0040h-005fh is reserved for the simulated 'interrupt
-- vectors', a total of 4 bytes for each of the 8 sources. This allows the 
-- software to easily test different interrupt vectors without any hand 
-- assembly. All of this is strictly simulation-only stuff.
--
-- Upon completion, the software must write a value to register 0x020. Writing 
-- a 0x055 means 'success', writing a 0x0aa means 'failure'. The write operation
-- will stop the simulation. Success and failure conditions are defined by the 
-- software.
--
-- If a time period defined as constant MAX_SIM_LENGTH passes before anything
-- is written to io address 0x020, the test bench assumes the software ran away
-- and quits with an error message.
--------------------------------------------------------------------------------
 
library ieee;
use ieee.std_logic_1164.ALL;
use ieee.std_logic_unsigned.all;
use ieee.numeric_std.ALL;
 
entity light8080_@PROGNAME@ is
end entity light8080_@PROGNAME@;
 
architecture behavior of light8080_@PROGNAME@ is
 
--------------------------------------------------------------------------------
-- Simulation parameters
 
-- T: simulated clock period
constant T : time := 100 ns;
 
-- MAX_SIM_LENGTH: maximum simulation time
constant MAX_SIM_LENGTH : time := T*7000; -- enough for the tb0
 
 
--------------------------------------------------------------------------------
 
signal data_i :           std_logic_vector(7 downto 0) := (others=>'0');
signal vma_o  :           std_logic;
signal rd_o :             std_logic;
signal wr_o :             std_logic;
signal io_o :             std_logic;
signal data_o :           std_logic_vector(7 downto 0);
signal data_mem :         std_logic_vector(7 downto 0);
signal addr_o :           std_logic_vector(15 downto 0);
signal fetch_o :          std_logic;
signal inta_o :           std_logic;
signal inte_o :           std_logic;
signal intr_i :           std_logic := '0';
signal halt_o :           std_logic;
 
signal reset :            std_logic := '0';
signal clk :              std_logic := '1';
signal done :             std_logic := '0';
 
type t_obj_code is array(integer range <>) of std_logic_vector(7 downto 0);
 
-- 
signal obj_code : t_obj_code(0 to 6143) := (
 
--@rom_data
 
);
 
signal irq_vector_byte:   std_logic_vector(7 downto 0);
signal irq_source :       integer range 0 to 7;
signal cycles_to_intr :   integer range -10 to 255;
signal intr_width :       integer range 0 to 255;
signal int_vector_index : integer range 0 to 3;
signal addr_vector_table: integer range 0 to 65535;
 
signal con_line_buf :     string(1 to 80);
signal con_line_ix :      integer;
 
 
 
type t_ram is array(0 to 65536-1) of std_logic_vector(7 downto 0);
 
-- Using shared variables for big memory arrays speeds up simulation a lot;
-- see Modelsim 6.3 User Manual, section on 'Modelling Memory'.
-- WARNING: I have only tested this construct with Modelsim SE 6.3.
shared variable ram : t_ram := ( others => X"00");
 
procedure load_object_code(
                signal obj :    in t_obj_code;
                memory :        inout t_ram) is
variable i : integer;
begin
 
  -- (Assume the array is defined with ascending indices)
  for i in obj'left to obj'right loop
    memory(i) := obj(i);
  end loop;
 
end procedure load_object_code;
 
 
 
begin
 
  -- Instantiate the Unit Under Test (UUT)
  cpu: entity work.light8080 
  port map (
    clk => clk,
    reset => reset,
    vma => vma_o,
    rd => rd_o,
    wr => wr_o,
    io => io_o,
    fetch => fetch_o,
    addr_out => addr_o, 
    data_in => data_i,
    data_out => data_o,
 
    intr => intr_i,
    inte => inte_o,
    inta => inta_o,
    halt => halt_o
  );
 
 
-- clock: run clock until test is done
clock:
process(done, clk)
begin
  if done = '0' then
    clk <= not clk after T/2;
  end if;
end process clock;
 
 
-- Drive reset and done 
main_test:
process
begin
  -- Load object code on memory -- note this comsumes no simulated time
  load_object_code(obj_code, ram);
 
  -- Assert reset for at least one full clk period
  reset <= '1';
  wait until clk = '1';
  wait for T/2;
  reset <= '0';
 
  -- Remember to 'cut away' the preceding 3 clk semiperiods from 
  -- the wait statement...
  wait for (MAX_SIM_LENGTH - T*1.5);
 
  -- Maximum sim time elapsed, assume the program ran away and
  -- stop the clk process asserting 'done' (which will stop the simulation)
  done <= '1';
 
  assert (done = '1') 
  report "Test timed out."
  severity failure;
 
  wait;
end process main_test;
 
 
-- Synchronous RAM covering the whole address map
synchronous_ram:
process(clk)
begin
  if (clk'event and clk='1') then
    data_mem <= ram(conv_integer(addr_o));
    if wr_o = '1' then
      ram(conv_integer(addr_o)) := data_o;
    end if;  
  end if;
end process synchronous_ram;
 
 
irq_trigger_register:
process(clk)
begin
  if (clk'event and clk='1') then
    if reset='1' then
      cycles_to_intr <= -10; -- meaning no interrupt pending
    else
      if io_o='1' and wr_o='1' and addr_o(7 downto 0)=X"11" then
        cycles_to_intr <= conv_integer(data_o) + 1;
      else
        if cycles_to_intr >= 0 then
          cycles_to_intr <= cycles_to_intr - 1;
        end if;
      end if;
    end if;
  end if;
end process irq_trigger_register;
 
irq_pulse_width_register:
process(clk)
variable intr_pulse_countdown : integer;
begin
  if (clk'event and clk='1') then
    if reset='1' then
      intr_width <= 1;
      intr_pulse_countdown := 0;
      intr_i <= '0';
    else
      if io_o='1' and wr_o='1' and addr_o(7 downto 0)=X"12" then
        intr_width <= conv_integer(data_o) + 1;
      end if;
 
      if cycles_to_intr = 0 then
        intr_i <= '1';
        intr_pulse_countdown := intr_width;
      elsif intr_pulse_countdown <= 1 then
        intr_i <= '0';
      else
        intr_pulse_countdown := intr_pulse_countdown - 1;
      end if;
    end if;
  end if;
end process irq_pulse_width_register;
 
irq_source_register:
process(clk)
begin
  if (clk'event and clk='1') then
    if reset='1' then
      irq_source <= 0;
    else
      if io_o='1' and wr_o='1' and addr_o(7 downto 0)=X"10" then
        irq_source <= conv_integer(data_o(2 downto 0));
      end if;
    end if;
  end if;
end process irq_source_register;
 
 
-- 'interrupt vector' logic.
irq_vector_table:
process(clk)
begin
  if (clk'event and clk='1') then
    if vma_o = '1' and rd_o='1' then
      if inta_o = '1' then
        int_vector_index <= int_vector_index + 1;
      else
        int_vector_index <= 0;
      end if;
    end if;
    -- this is the address of the byte we'll feed to the CPU
    addr_vector_table <= 64+irq_source*4+int_vector_index;
  end if;
end process irq_vector_table;
irq_vector_byte <= ram(addr_vector_table);
 
data_i <= data_mem when inta_o='0' else irq_vector_byte;
 
 
test_outcome_register:
process(clk)
variable outcome : std_logic_vector(7 downto 0);
begin
  if (clk'event and clk='1') then
    if io_o='1' and wr_o='1' and addr_o(7 downto 0)=X"20" then
    assert (data_o /= X"55") report "Software reports SUCCESS" severity failure;
    assert (data_o /= X"aa") report "Software reports FAILURE" severity failure;
    assert ((data_o = X"aa") or (data_o = X"55")) 
    report "Software reports unexpected outcome value." 
    severity failure;
    end if;
  end if;
end process test_outcome_register;
 
 
dummy_uart_output_reg:
process(clk)
variable outcome : std_logic_vector(7 downto 0);
begin
  if (clk'event and clk='1') then
    if io_o='1' and wr_o='1' and addr_o(7 downto 0)=X"21" then
      -- append char to output string
      if con_line_ix < con_line_buf'high then
        con_line_buf(con_line_ix) <= character'val(conv_integer(data_o));
        con_line_ix <= con_line_ix + 1;
      end if;
    end if;
  end if;
end process dummy_uart_output_reg;
 
 
end;