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[/] [light8080/] [trunk/] [vhdl/] [test/] [tb_template.vhdl] - Rev 68
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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\hexconv.pl' 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 := ( --@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; begin -- 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 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 -- 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; 2KB mirrored everywhere synchronous_ram: process(clk) begin 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; 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 <= rom(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; end;
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