I'm trying out some code that essentially involves using an FPGA and reading values from a temperature sensor.
The code is below:
library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL; ---- Uncomment the following library declaration if instantiating ---- any Xilinx primitives in this code. --library UNISIM; --use UNISIM.VComponents.all; entity ds18b20 is Port ( clk : in STD_LOGIC; --50Mhz oscillator onboard dq : inout STD_LOGIC; temp_h : out STD_LOGIC_VECTOR (7 downto 0); temp_l : out STD_LOGIC_VECTOR (7 downto 0); temperature : out STD_LOGIC_VECTOR (11 downto 0)); end ds18b20; architecture Behavioral of ds18b20 is --RESET : RESET AND PRESENCE PULSE --CMD_CC : SKIP ROM [CCh] --WRITE_BYTE : WRITE SCRATCHPAD COMMAND --WRITE_LOW --WRITE_HIGH --READ_BIT : TYPE STATE_TYPE is (RESET,CMD_CC,WRITE_BYTE,WRITE_LOW,WRITE_HIGH,READ_BIT,CMD_44,WAIT800MS,CMD_BE,GET_TMP,WAIT4MS); signal STATE: STATE_TYPE:=RESET; signal clk_temp : std_logic:='0'; signal clk1m : std_logic; signal write_temp : std_logic_vector(7 downto 0) := (others => '0'); signal TMP : std_logic_vector(11 downto 0); signal tmp_bit : std_logic; signal WRITE_BYTE_CNT : integer range 0 to 8:=0; signal WRITE_LOW_CNT : integer range 0 to 2:=0; signal WRITE_HIGH_CNT : integer range 0 to 2:=0; signal READ_BIT_CNT : integer range 0 to 3:=0; signal GET_TMP_CNT : integer range 0 to 12:=0; signal cnt : integer range 0 to 100001:=0; signal count : integer range 0 to 25:=0; signal WRITE_BYTE_FLAG : integer range 0 to 4:=0; begin ClkDivider: process (clk) begin if rising_edge(clk) then if (count = 24) then count <= 0; clk_temp<= not clk_temp; else count <= count +1; end if; end if; clk1m<=clk_temp; end Process; STATE_TRANSITION: process(STATE,clk) begin if rising_edge(clk) then case STATE is --Master issues RESET pulse when RESET=> if (cnt>=0 and cnt<500) then dq<='0'; cnt<=cnt+1; STATE<=RESET; --Master waits for PRESENCE pulse elsif (cnt>=500 and cnt<1000) then dq<='Z'; cnt<=cnt+1; STATE<=RESET; elsif (cnt>=1000) then cnt<=0; STATE<=CMD_CC; -- SKIP ROM COMMAND STATE end if; when CMD_CC=> -- SKIP ROM COMMAND write_temp<="11001100"; -- SKIP ROM BINARY COMMAND STATE<=WRITE_BYTE; -- modified here --Master issues write scratchpad command when WRITE_BYTE=> case WRITE_BYTE_CNT is when 0 to 7=> if (write_temp(WRITE_BYTE_CNT)='0') then STATE<=WRITE_LOW; else STATE<=WRITE_HIGH; end if; WRITE_BYTE_CNT<=WRITE_BYTE_CNT+1; when 8=> if (WRITE_BYTE_FLAG=0) then -- ????0XCC?? STATE<=CMD_44; --CONVERT TEMPERATURE WRITE_BYTE_FLAG<=1; elsif (WRITE_BYTE_FLAG=1) then --?0X44?? STATE<=RESET; WRITE_BYTE_FLAG<=2; elsif (WRITE_BYTE_FLAG=2) then --????0XCC?? STATE<=CMD_BE; -- READ SCRATCHPAD WRITE_BYTE_FLAG<=3; elsif (WRITE_BYTE_FLAG=3) then --?0XBE?? STATE<=GET_TMP; WRITE_BYTE_FLAG<=0; end if; WRITE_BYTE_CNT<=0; end case; when WRITE_LOW=> case WRITE_LOW_CNT is when 0=> dq<='0'; if (cnt=78) then cnt<=0; WRITE_LOW_CNT<=1; else cnt<=cnt+1; end if; when 1=> dq<='Z'; if (cnt=2) then cnt<=0; WRITE_LOW_CNT<=2; else cnt<=cnt+1; end if; when 2=> STATE<=WRITE_BYTE; WRITE_LOW_CNT<=0; when others=>WRITE_LOW_CNT<=0; end case; when WRITE_HIGH=> case WRITE_HIGH_CNT is when 0=> dq<='0'; if (cnt=8) then cnt<=0; WRITE_HIGH_CNT<=1; else cnt<=cnt+1; end if; when 1=> dq<='Z'; if (cnt=72) then cnt<=0; WRITE_HIGH_CNT<=2; else cnt<=cnt+1; end if; when 2=> STATE<=WRITE_BYTE; WRITE_HIGH_CNT<=0; when others=>WRITE_HIGH_CNT<=0; end case; when READ_BIT=> case READ_BIT_CNT is when 0=> dq<='0'; if (cnt=4) then READ_BIT_CNT<=1; cnt<=0; else cnt<=cnt+1; end if; when 1=> dq<='Z'; if (cnt=4) then READ_BIT_CNT<=2; cnt<=0; else cnt<=cnt+1; end if; when 2=> TMP_BIT<=dq; if (cnt=1) then READ_BIT_CNT<=3; cnt<=0; else cnt<=cnt+1; end if; when 3=> if (cnt=45) then cnt<=0; READ_BIT_CNT<=0; STATE<=GET_TMP; else cnt<=cnt+1; end if; when others=>READ_BIT_CNT<=0; end case; when CMD_44=> -- CONVERT TEMPERATURE write_temp<="01000100"; -- CONVERT TEMPERATURE BINARY COMMAND STATE<=WRITE_BYTE; when WAIT800MS=> if (cnt>=100000) then STATE<=RESET; cnt<=0; else cnt<=cnt+1; STATE<=WAIT800MS; end if; when CMD_BE=> -- READ SCRATCHPAD write_temp<="10111110"; -- READ SCRATHPAD BINARY COMMAND STATE<=WRITE_BYTE; when GET_TMP=> case GET_TMP_CNT is when 0 to 11=> STATE<=READ_BIT; TMP(GET_TMP_CNT)<=TMP_BIT; GET_TMP_CNT<=GET_TMP_CNT+1; when 12=> GET_TMP_CNT<=0; STATE<=WAIT4MS; end case; when WAIT4MS=> if (cnt>=4000) then STATE<=RESET; cnt<=0; else cnt<=cnt+1; STATE<=WAIT4MS; end if; when others=>STATE<=RESET; end case; end if; end process; temp_h<='0'&TMP(11 downto 5); temp_l<="0000"&TMP(4 downto 1); temperature <= TMP; end Behavioral; The warning I get is
WARNING:Xst:1293 - FF/Latch <write_temp_0> has a constant value of 0 in block <ds18b20>. This FF/Latch will be trimmed during the optimization process. WARNING:Xst:1710 - FF/Latch <Mtridata_dq> (without init value) has a constant value of 0 in block <ds18b20>. This FF/Latch will be trimmed during the optimization process. write_temp is a variable that holds the binary commands for the sensor. So essentially, I will be sending these commands to the sensor via the "dq" bidirectional port. Now, the warning states that write_temp is always 0 which means I can't instruct the sensor to do any operation at all since its always 0.
Could anyone please shed some light on how to overcome this? Much appreciated.