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[/] [light8080/] [trunk/] [vhdl/] [test/] [tb_template.vhdl] - Rev 40

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-- 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\@PROGNAME@.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 2KB of RAM, mirror-mapped to all the memory 
-- map of the 8080, initialized with the test program object code. See the perl
-- script 'util\' and BAT files in the asm directory.
-- Besides, it 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.
-- 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
-- Component Declaration for the Unit Under Test (UUT)
component light8080
  port (  
    addr_out :  out std_logic_vector(15 downto 0);
    inta :      out std_logic;
    inte :      out std_logic;
    halt :      out std_logic;                
    intr :      in std_logic;
    vma :       out std_logic;
    io :        out std_logic;
    rd :        out std_logic;
    wr :        out std_logic;
    fetch :     out std_logic;
    data_in :   in std_logic_vector(7 downto 0);  
    data_out :  out std_logic_vector(7 downto 0);
    clk :       in std_logic;
    reset :     in std_logic );
end component;
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_rom is array(0 to 2047) of std_logic_vector(7 downto 0);
signal rom : t_rom := (
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;
	-- Instantiate the Unit Under Test (UUT)
	uut: 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
process(done, clk)
	if done = '0' then
		clk <= not clk after T/2;
	end if;
end process clock;
-- Drive reset and done 
	-- 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;
end process main_test;
-- Synchronous RAM; 2KB mirrored everywhere
  if (clk'event and clk='1') then
    data_mem <= rom(conv_integer(addr_o(10 downto 0)));
    if wr_o = '1' and addr_o(15 downto 11)="00000" then
      rom(conv_integer(addr_o(10 downto 0))) <= data_o;
    end if;  
  end if;
end process synchronous_ram;
  if (clk'event and clk='1') then
    if reset='1' then
      cycles_to_intr <= -10; -- meaning no interrupt pending
      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;
        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;
variable intr_pulse_countdown : integer;
  if (clk'event and clk='1') then
    if reset='1' then
      intr_width <= 1;
      intr_pulse_countdown := 0;
      intr_i <= '0';
      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';
        intr_pulse_countdown := intr_pulse_countdown - 1;
      end if;
    end if;
  end if;
end process irq_pulse_width_register;
  if (clk'event and clk='1') then
    if reset='1' then
      irq_source <= 0;
      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.
  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;
        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 <= rom(addr_vector_table);
data_i <= data_mem when inta_o='0' else irq_vector_byte;
variable outcome : std_logic_vector(7 downto 0);
  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;

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