currently I am trying to write a VHDL wrapper for this Opencore Verilog module (1-wire master) so that I can send/receive from this temperature sensor (DS18B20).
However I am struggling to understand the usage. Namely the read/write enable vs. the cyc bit in the control/status register of the 1-wire master module.
The code I have so far sets the cyc bit to 1 and the read/write enable to one simultaneously but does not cycle them during each bit. Is this correct or am I misunderstanding it? I'm new to VHDL/ reading a datasheet so I have been struggling over this for a few days. Any help would be appreciated.
I found this site that I have been using as a reference but it does not deal with the Verilog module that I am using.
I am also looking for tips on my code style, and VHDL tips in general.
My current code:
LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL; --may need to remove if signed not used
ENTITY one_wire_temp_probe_control IS
GENERIC (
one_us_divider_g : integer range 0 to 50 := 50 -- clock divider for one micro second
);
PORT (
i_clk_50mhz : IN STD_LOGIC;
i_read_enable : IN std_logic;
io_temp_probe : INOUT STD_LOGIC; --how do i register an inout
o_temperature : OUT signed(6 DOWNTO 0);
o_temp_ready : OUT std_logic
);
END one_wire_temp_probe_control;
ARCHITECTURE rtl of one_wire_temp_probe_control IS
----temp commands----
CONSTANT skip_rom_c : std_logic_vector(7 DOWNTO 0) := x"CC"; --command to skip ROM identity of temperature sensor
CONSTANT convert_temp_c : std_logic_vector(7 DOWNTO 0) := x"44"; --command to start temperature conversion
CONSTANT read_scratchpad_c : std_logic_vector(7 DOWNTO 0) := x"BE"; --command to read the scratchpad i.e. get temperature data
CONSTANT command_bits_c : integer RANGE 0 TO 8 := 8; --number of bits in the above commands (note: range used to limit number of bits to minimum needed)
CONSTANT data_bits_c : integer RANGE 0 to 12 := 12; --number of bits in received data
----1-wire commands----
CONSTANT send_reset_pulse : std_logic_vector(7 DOWNTO 0) := "00001010"; --command to send reset pulse
CONSTANT write_command_structure_c : std_logic_vector(6 DOWNTO 0) := "0000000"; --structure of the command that must be passed to the 1-wire controller (----EDIT----)
----timing constants----
CONSTANT delay_65us_c : integer := one_us_divider_g * 65; --65 micro-second delay
CONSTANT delay_960us_c : integer := one_us_divider_g * 960; --960 micro-second delay
CONSTANT delay_750ms : integer := one_us_divider_g * 1000 * 750; --760 milli-second delay
----state machine----
TYPE state_type IS (idle, presence_pulse, wait_presence_pulse, skip_rom, temp_conversion, wait_for_conversion,
read_scratchpad, data_read, convert_data, wait_65us);
SIGNAL state : state_type := idle;
SIGNAL previous_state : state_type := idle;
----1-wire----
SIGNAL read_enable_s, write_enable_s, reset_s, owr_e_s : std_logic := '0';
SIGNAL write_data_s, read_data_s : std_logic_vector(7 DOWNTO 0):= (OTHERS => '0'); --8 bit mode chosen in sockit_owm
SIGNAL address_s : std_logic_vector(1 DOWNTO 0) := "00";
SIGNAL timer_s : integer := 0;
----commands---
SIGNAL bit_counter_command_s : integer RANGE 0 TO command_bits_c := 0; --counter for bits in commands (note: not -1 due to using 9th bit as state change)
SIGNAL bit_counter_data_s : integer RANGE 0 TO data_bits_c := 0; --counter for bits in data recieved
----temperature----
SIGNAL temperature_raw_data : std_logic_vector(11 DOWNTO 0) := (OTHERS => '0');
----one wire control----
COMPONENT sockit_owm IS
PORT (
----control interface----
clk : IN std_logic;
rst : IN std_logic;
bus_ren : IN std_logic;
bus_wen : IN std_logic;
bus_adr : IN std_logic_vector(7 DOWNTO 0);
bus_wdt : IN std_logic_vector(7 DOWNTO 0);
bus_rdt : OUT std_logic_vector(7 DOWNTO 0);
bus_irq : OUT std_logic;
----1-wire interface----
owr_p : OUT std_logic; --verilog code is a one bit wide vector
owr_e : OUT std_logic;
owr_i : IN std_logic
);
END COMPONENT;
BEGIN
address_s <= "00"; --for the temp probe control we're not interested in other address spaces
PROCESS(i_clk_50mhz) BEGIN --state change
IF rising_edge(i_clk_50mhz) THEN
CASE state is
WHEN idle =>
o_temp_ready <= '0';
IF (i_read_enable = '1') THEN
state <= presence_pulse;
ELSE
state <= idle;
END IF;
WHEN presence_pulse =>
----send reset/presence pulse----
write_enable_s <= '1';
write_data_s <= send_reset_pulse;
timer_s <= delay_960us_c;
state <= wait_presence_pulse;
WHEN wait_presence_pulse =>
----wait for 960 micro seconds----
read_enable_s <= '1';
IF (timer_s = 0) THEN
IF (read_data_s(0) = '0') THEN
state <= skip_rom;
ELSIF (read_data_s(0) = '1') THEN
--precence not detected
ELSE
state <= wait_presence_pulse;
END IF;
ELSE
timer_s <= timer_s - 1;
state <= wait_presence_pulse;
END IF;
WHEN skip_rom =>
----send skip rom command----
previous_state <= skip_rom;
write_enable_s <= '1';
IF (bit_counter_command_s = command_bits_c) THEN
bit_counter_command_s <= 0;
state <= temp_conversion;
ELSE
write_data_s <= write_command_structure_c & skip_rom_c(bit_counter_command_s); ---command structure concatonated with 1 bit from command
bit_counter_command_s <= bit_counter_command_s + 1;
timer_s <= delay_65us_c;
state <= wait_65us;
END IF;
WHEN temp_conversion =>
----send temp conversion command to probe----
previous_state <= temp_conversion;
IF (bit_counter_command_s = bit_counter_command_s) THEN
bit_counter_command_s <= 0;
timer_s <= delay_750ms;
state <= wait_for_conversion;
ELSE
write_data_s <= write_command_structure_c & convert_temp_c(bit_counter_command_s); ---command structure concatonated with 1 bit from command
bit_counter_command_s <= bit_counter_command_s + 1;
timer_s <= delay_65us_c;
state <= wait_65us;
END IF;
WHEN wait_for_conversion =>
----wait for temperature conversion to finish----
IF (timer_s = 0) then
state <= read_scratchpad;
ELSE
timer_s <= timer_s - 1;
END IF;
WHEN read_scratchpad =>
----send read scratchpad command----
previous_state <= read_scratchpad;
IF (bit_counter_command_s = command_bits_c) THEN
state <= data_read;
bit_counter_command_s <= 0;
ELSE
write_data_s <= write_command_structure_c & read_scratchpad_c(bit_counter_command_s); ---command structure concatonated with 1 bit from command
bit_counter_command_s <= bit_counter_command_s + 1;
timer_s <= delay_65us_c;
state <= wait_65us;
END IF;
WHEN data_read =>
----read incoming data----
previous_state <= data_read;
read_enable_s <= '1';
IF (bit_counter_data_s = data_bits_c) THEN
bit_counter_data_s <= 0; --may need to invert this
state <= convert_data;
ELSE
temperature_raw_data(bit_counter_data_s) <= read_data_s(0);
bit_counter_data_s <= bit_counter_data_s + 1;
timer_s <= delay_65us_c;
state <= wait_65us;
END IF;
WHEN convert_data =>
----convert raw data into temperature----
o_temp_ready <= '1';
WHEN wait_65us =>
----wait for read/write cycle to finish----
IF (timer_s = 0) THEN
state <= previous_state;
ELSE
timer_s <= timer_s - 1;
state <= wait_65us;
END IF;
END CASE;
END IF;
END PROCESS;
----one wire component instantiation----
one_wire_control : sockit_owm
PORT MAP(
----control interface----
clk => i_clk_50mhz,
rst => reset_s,
bus_ren => read_enable_s,
bus_wen => write_enable_s,
bus_adr => address_s,
bus_wdt => write_data_s,
bus_rdt => read_data_s,
bus_irq => OPEN,
----1-wire interface----
owr_p => OPEN,
owr_e => owr_e_s,
owr_i => io_temp_probe
);
io_temp_probe <= owr_e_s ? '0' : 'Z'; --I also need help converting this line to VHDL
END rtl;
Thank you in advance. Best Tom
I am also looking for tips on my code style, and VHDL tips in general.
OK.
First thing: don't make the lines so long. So don't put comments at the end of a line. Put them a line before.
use IEEE.NUMERIC_STD.ALL; --may need to remove if signed not used
then remove, as I don't see any signed
one_us_divider_g : integer range 0 to 50 := 50 -- clock divider for one micro second
So... what happens is one_us_divider_g is set to 0? Seems an illegal value. Using it for simulation?
io_temp_probe : INOUT STD_LOGIC; --how do i register an inout
One option is to use a tristate IOBUFFER. This is a special FPGA edge element which splits the input and output to separate signals. You can tristate the ouput by setting a control port.
Alternatively you could just do it the way you do in your code (this is also explained in for instance the Xilinx synthesis user guide). Which leads me to another question in your code.
io_temp_probe <= owr_e_s ? '0' : 'Z'; --I also need help converting this line to VHDL
io_temp_probe <= '0' when owr_e_s = '1' else 'Z';
CONSTANT command_bits_c : integer RANGE 0 TO 8 := 8;
No need for an integer range if it is a constant.
CONSTANT send_reset_pulse : ...
CONSTANT delay_750ms : ...
Missing the "_c" you put behind all your constants. But I would not add this "s", "_c" or "_g" anyhow. A lot of work for little gain.
COMPONENT sockit_owm IS
PORT (
[...]
);
END COMPONENT;
Component declarations are not required anymore since some time now. You can remove it and change your instantiation:
one_wire_control : entity work.sockit_owm
PORT MAP(
[...]
WHEN idle =>
[...]
ELSE
state <= idle;
END IF;
not required. If you don't change state, it stays at idle.
WHEN wait_presence_pulse =>
IF (timer_s = 0) THEN
IF (read_data_s(0) = '0') THEN
[...]
ELSIF (read_data_s(0) = '1') THEN
[...]
ELSE
state <= wait_presence_pulse;
END IF;
read_data_s(0) '0' and '1' are covered. Do you expect any other value? That can only happen in simulation, not in implementation. So the code in the last else-statement is unreachable then.
[...]
timer_s <= delay_65us_c;
state <= wait_65us;
[...]
WHEN wait_65us =>
IF (timer_s = 0) THEN
[...]
ELSE
timer_s <= timer_s - 1;
END IF;
Let's say a delay is 65 us lasts 10 clock cycles. Setting the divider to 1, delay_65us_c=10. So at t=0, timer_s is set to 10. at t=1 -state is wait_65us now- timer_s is set to 9. And so on: at t=10, timer_s is set to 0... but state is still wait_65us. So at t=11, timer_s is detected 0, and state is changed to the previous one. Which it will enter at t=12.
So, instead of a 10 clock cycle delay, you get a 12 clock cycle delay.
Is this a problem? If yes, you should reconsider your code.
SIGNAL read_enable_s, write_enable_s, reset_s, owr_e_s : std_logic := '0';
[... not used anywhere else... ]
one_wire_control : sockit_owm
PORT MAP(
[...]
rst => reset_s,
Are you sure this is correct? A lot of components need to be properly reset before they operate correctly.