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/trunk/vhdl/test/tb_template.vhdl
0,0 → 1,264
--------------------------------------------------------------------------------
-- Light8080 simulation test bench.
--------------------------------------------------------------------------------
-- Source for the 8080 program is in 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 registers 0x010 and 0x011. Register 0x010 holds the irq
-- source to be triggered (0 to 7) and register 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.
--
-- 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'. Success and
-- failure conditions are defined by the software.
--------------------------------------------------------------------------------
 
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 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
intr_i <= '0';
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;
if cycles_to_intr = 0 then
intr_i <= '1';
else
intr_i <= '0';
end if;
end if;
end if;
end if;
end process irq_trigger_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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