Description
Hi,
I have encountered a bug where simulation craches with " Caught signal 11 (SEGV_MAPERR)". It gives no other error message syntax issue etc. I tracked down the cause to accessing out of range on a custom type like below. In the code below, the range of state_array is 0 to "read_size -1" . In the for generate, the range 0 to "write_size - 1" is tried to be accessed. when "read_size" is smaller than the "write_size" simulation chashes. I tried the same for the variable "test_out" but it gave the correct range warnings and did not crash. I noticed that the simulation does not crash if you remove the "reset" on the process. I have used cocotb for simulation.
`
library IEEE;
use IEEE.STD_LOGIC_1164.all;
use IEEE.NUMERIC_STD.all;
library work;
entity nvc_bug is
generic (
read_size : integer := 2;
write_size : integer := 16
);
port (
clk : in std_logic;
reset : in std_logic;
write_en : in std_logic_vector(write_size -1 downto 0);
test_out : out std_logic_vector(write_size -1 downto 0)
);
end nvc_bug;
architecture Behavioral of nvc_bug is
-- Attribute definitions
type state_t is (idle, test_0, test_1, test_2, test_3);
type state_array_t is array (0 to read_size - 1) of state_t;
signal state_array : state_array_t;
begin
bug_generator: for i in 0 to write_size - 1 generate
process (clk)
begin
if rising_edge(clk) then
if(reset = '1')then
state_array(i) <= idle;
test_out(i) <= '0';
else
case state_array(i) is
when idle =>
if(write_en(i) = '1')then
state_array(i) <= test_0;
test_out(i) <= '1';
else
state_array(i) <= idle;
test_out(i) <= '0';
end if;
when test_0 =>
state_array(i) <= test_1;
test_out(i) <= '1';
when test_1 =>
state_array(i) <= test_2;
test_out(i) <= '0';
when test_2 =>
state_array(i) <= test_3;
test_out(i) <= '1';
when test_3 =>
state_array(i) <= idle;
test_out(i) <= '0';
when others =>
end case;
end if;
end if;
end process;
end generate;
end Behavioral;
`