Comments on my code

[daveip]

Hi ... I'm hoping someone could comment on my code.
It compiles fine in model sim but I just don't think it'll work

Anywhos ... here it is:

------------------------------------------------------------------

ibrary IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_unsigned.all;
use IEEE.Numeric_STD.all;

entity statemachine is
port(
clock : in std_logic;
reset : in std_logic;
in_pin : in std_logic;
out_pin: in std_logic;
empty : out std_logic;
full : out std_logic;
err : out std_logic;
number : out std_logic_vector (7 downto 0)
);
end;

architecture struct of statemachine is

type state is (S_ERROR, S_FULL, S_EMPTY, S_ADD, S_SUB, S_NORMAL); -- 11 states
signal next_state,current_state : state;


begin

--------------------------------
-- RESET PROCEDURE
--------------------------------

zero : process(clock)
begin
if (reset = '1') then
current_state <= S_EMPTY; --go to empty state
number <= "00000000"; --reset counter to zerp
err <= '0'; --error value = 0
full <= '0'; --full = 0
empty <= '1'; --empty = 1 as full reset
elsif rising_edge(clock) then
current_state <= next_state; --on each clock cycle, move to next state
else null;
end if;
end process zero;


------------------------------
-- STATE MACHINE
------------------------------

states : process(current_state, in_pin, out_pin)

variable v_state : state;
variable v_err, v_full, v_empty : std_logic;
variable v_number : std_logic_vector(7 downto 0);

begin

case v_state is

when S_ERROR =>
v_err := '1';
v_state := S_ERROR;

when S_FULL =>
if (in_pin = '1') then
v_state := S_ERROR;
elsif (out_pin = '1') then
v_number := v_number - 1;
v_state := S_NORMAL;
else null;
end if;


when S_EMPTY =>
if (out_pin = '1') then
v_state := S_ERROR;
elsif (in_pin = '1') then
v_number := v_number + 1;
v_state := S_NORMAL;
else null;
end if;


when S_ADD =>
if (v_number = "11111110") then
v_number := "11111111";
v_state := S_FULL;
else
v_number := v_number + 1;
v_state := S_NORMAL;
end if;

when S_SUB =>
if (v_number = "00000001") then
v_number := "00000000";
v_state := S_EMPTY;
else
v_number := v_number - 1;
v_state := S_NORMAL;
end if;

when S_NORMAL =>
v_full := '0';
v_empty := '0';
if rising_edge(in_pin) then
v_state := S_ADD;
elsif rising_edge(out_pin) then
v_state := S_SUB;
else null;
end if;

when others => null;


end case;

next_state <= v_state;
err <= v_err;
full <= v_full;
empty <= v_empty;
number <= v_number;


end process;

end struct;

-------------------------------------------------------------------

Its been a while since I played with VHDL. I can't remember how to assign the initial state without assigning 1 to the reset pin.

Anything constructive is welcomed =)

 

[jeppe]

These lines are the bad ones from a synthesize point of view - but for simulation are the ok.
The process surposed to produce combinatirial logic but you mix it with edge sentive stuff.

The if rising_edge .... then .... elsif rising_edge ... will aways give you errors.

Rething your design.

v_full := '0';
v_empty := '0';
if rising_edge(in_pin) then
v_state := S_ADD;
elsif rising_edge(out_pin) then
v_state := S_SUB;
else null;
end if;

your welcome
Jeppe

 

[daveip]

Thanks for your reply Jeppe.

Yeah I know that it won't synthesise.

The task I've been set is to implement the VHDL code in Xilinx and build timing constraints from Xilinx to return back to modelsim to simulate it. If that makes sense =S

I'm not sure how else to implement the input signals. My lecturer hasn't described to me the way the input signal is triggered and for how long. I have to make assumptions and I'm assuming that for each item that passes a sensor, the best way to count them would be the use of edge triggers.

I'm thinking of possibly adding a "holding state" where the machine waits for either signal to fall back to zero. But my problem there would be this situation: if the item is triggering the sensor on the in_pin and the machine enters the holding state, it will miss anything passing the out_pin whilst it's still in this state.

I'm abit stuck as to how best to implement this code =/

 

[daveip]

I think i have it figured?

I'll have to detect the edge somehow and hold that value for just 1 clock cycle. .... how i haven't figured yet =/

 

[daveip]

library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_unsigned.all;
use IEEE.Numeric_STD.all;

entity statemachine is
    port( 
        clock : in std_logic;
        reset : in std_logic;
        in_pin : in std_logic;
        out_pin: in std_logic;
        empty : out std_logic;
        full : out std_logic;
        err : out std_logic;
        number : out std_logic_vector (7 downto 0)
        );
    end;

architecture struct of statemachine is

type state is (S_ERROR, S_FULL, S_EMPTY, S_ADD, S_SUB, S_NORMAL);  
signal next_state,current_state : state;
signal s_in, s_out : std_logic;


begin
    
--------------------------------
-- RESET PROCEDURE
--------------------------------

zero : process(clock,reset)
begin
    if (reset = '1') then        
        number <= "11111111";          --reset counter to zerp
        err <= '0';                    --error value = 0
        full <= '0';                   --full = 0
        empty <= '1';                  --empty = 1 as full reset
        current_state <= S_EMPTY;      --go to empty state
        elsif rising_edge(clock) then
            current_state <= next_state;
    end if;
end process zero;

    
in_latch : process(clock,in_pin)
begin
    if rising_edge(in_pin) then
        s_in <= '1';
        else
        s_in <= '0';
    end if;
end process;

out_latch : process(clock,out_pin)
begin
    if rising_edge(out_pin) then
        s_out <= '1';
        else
        s_out <= '0';
    end if;
end process;
    
    
------------------------------
-- STATE MACHINE
------------------------------

states : process(current_state, s_in, s_out)

variable v_state : state;
variable v_err, v_full, v_empty : std_logic;
variable v_number : std_logic_vector(7 downto 0);

begin
    
    case v_state is
        
        when S_EMPTY =>
            if (s_out = '1') then
                v_state := S_ERROR;
                elsif (s_in = '1') then
                    v_number := v_number + 1;
                    v_state := S_NORMAL;
                    else v_state := S_EMPTY;
                end if;
                
        when S_NORMAL =>
            v_full := '0';
            v_empty := '0';
            if (s_in = '1') then
                v_state := S_ADD;
            elsif (s_out = '1') then
                v_state := S_SUB;
                else null;
            end if;

        when S_ERROR =>
            v_err := '1';
            v_state := S_ERROR;
            
        when S_FULL =>
            if (s_in = '1') then
                v_state := S_ERROR;
                elsif (s_out = '1') then
                    v_number := v_number - 1;
                    v_state := S_NORMAL;
                    else null;
                end if;
            
        when S_ADD =>
            if (v_number = "11111110") then
                v_number := "11111111";
                v_state := S_FULL;
                else
                v_number := v_number + 1;
                v_state := S_NORMAL;
            end if;
            
        when S_SUB =>
            if (v_number = "00000001") then
                v_number := "00000000";
                v_state := S_EMPTY;
                else
                v_number := v_number - 1;
                v_state := S_NORMAL;
            end if;
            

        
        when others => null;
            
           
       end case;
       
    next_state <= v_state;
    err <= v_err;
    full <= v_full;
    empty <= v_empty;
    number <= v_number;                    

end process;

    
    
end struct;

there's the updated code. I've built a test bench for the machine but there's a problem i can't figure! I'm trying to assign the initial values of the outputs by resetting before doing anything.

the simulator isn't showing the updated outputs getting zeroed ... but leaving them undefined and next state seems to be stuck on my error state =/

i figured the latch and it works perfectly!!!

anyone able to lend a hand please?