I'm a student working on a project, on a custom designed board that has a Spartan-6 FPGA on board. My project is to make a game that outputs its interface through HDMI, and recieves input via a sensor. My sensor is the HC - SR04 (http://www.micropik.com/PDF/HCSR04.pdf). All modules are wokring, except for the sensor module. I'm not getting any warning or errors. The following shows my code for the module, in which I created a finite state machine to run through the stages required to send/receive data from the sensor. Note that I have an additional state than what is required in the datasheet, but that shouldn't be a problem since it doesn't trigger the sensor.
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;
entity Sensor is
Port ( clk : in STD_LOGIC; --24 MHz
Echo : in STD_LOGIC;
Trig : out STD_LOGIC;
Echo_Time: out integer
);
end Sensor;
architecture Behavioral of Sensor is
type state_type is ( Init_state, Trigger_state, Echo_state);
signal state : state_type := Init_state;
signal echoing : std_logic := '0'; -- determines if we are echoing or not
signal echoReceived : std_logic := '0'; -- determines if we are echoing or not
signal d : integer; -- the first and highest possible delay, this is 20 ms
signal en_timer : std_logic; --active high
signal rst_timer : std_logic; --active high
signal cnt_timer : integer := 0;--was 19,
signal final_timer : integer := 0;--was 19,
begin
state_machine: process (clk, cnt_timer, echoReceived)
begin
if rising_edge(clk) then
if state = Init_state then
if cnt_timer = d then
state <= Trigger_state;
rst_timer <= '1';
else
rst_timer <= '0';
end if;
elsif state = Trigger_state then
if cnt_timer = d then
state <= Echo_state;
rst_timer <= '1';
else
rst_timer <= '0';
end if;
elsif state = Echo_state then
if echoReceived = '1' then--change this one
state <= Init_state;
rst_timer <= '1';
else
rst_timer <= '0';
end if;
end if;
end if;
end process;
timer: process(clk, en_timer,rst_timer)
begin
if rising_edge(clk) then
if en_timer = '1' and rst_timer = '0' then
cnt_timer <= cnt_timer + 1;
elsif rst_timer = '1' then
cnt_timer <= 0;
end if;
end if;
end process;
state_machine_output: process(state, Echo, echoing,cnt_timer)
begin
--internal signals
en_timer <= '0';
--state machine signals
d <= 0;
echoing <= '0';
echoReceived <= '0';
final_timer <= 0;
--external signals
Trig <= '0';
if state = Init_state then
en_timer <= '1';
Trig <= '0';
d <= 48; -- this will delay the system by 2 us
echoing <= '0';
echoReceived <= '0';
elsif state = Trigger_state then
en_timer <= '1';
Trig <= '1';
d <= 240; -- this will delay the system by 10 us
echoing <= '0';
echoReceived <= '0';
elsif state = Echo_state then --think about it later
if Echo = '1' then
en_timer <= '1';
echoing <= '1';
elsif Echo = '0' and echoing = '1' then
final_timer <= cnt_timer;
en_timer <= '0';
echoing <= '0';
echoReceived <= '1';
end if;
else
--internal signals
en_timer <= '0';
--state machine signals
d <= 0;
echoing <= '0';
echoReceived <= '0';
final_timer <= 0;
--external signals
Trig <= '0';
end if;
end process;
Echo_Time <= final_timer;--output data here
end Behavioral;
So, my question is whether my logic here is correct or not, because I'm only getting 0 from Echo_time.
Also, note that the sensor is working fine with arduino.
Echo_time is always 0 because of these code lines:
if Echo = '1' then
en_timer <= '1';
echoing <= '1';
elsif Echo = '0' and echoing = '1' then
final_timer <= cnt_timer;
en_timer <= '0';
echoing <= '0';
echoReceived <= '1';
end if;
Trace the signal from the output:
Echo_time is equal to final_timer.final_timer is always 0 except if Echo = '0' and echoing = '1'Echo = '1'Echo is either 0 or 1, final timer can not be positive.