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Rev 72 → Rev 71

/rtl/vhdl/i2c_master_bit_ctrl.vhd
110,24 → 110,24
-- Each command has 5 states, A/B/C/D/idle
--
-- start: SCL ~~~~~~~~~~~~~~\____
-- SDA XX/~~~~~~~\______
-- x | A | B | C | D | i
-- SDA XX/~~~~~~~\______
-- x | A | B | C | D | i
--
-- repstart SCL ______/~~~~~~~\___
-- SDA __/~~~~~~~\______
-- x | A | B | C | D | i
-- SDA __/~~~~~~~\______
-- x | A | B | C | D | i
--
-- stop SCL _______/~~~~~~~~~~~
-- SDA ==\___________/~~~~~
-- x | A | B | C | D | i
-- SDA ==\___________/~~~~~
-- x | A | B | C | D | i
--
--- write SCL ______/~~~~~~~\____
-- SDA XXX===============XX
-- x | A | B | C | D | i
-- SDA XXX===============XX
-- x | A | B | C | D | i
--
--- read SCL ______/~~~~~~~\____
-- SDA XXXXXXX=XXXXXXXXXXX
-- x | A | B | C | D | i
-- SDA XXXXXXX=XXXXXXXXXXX
-- x | A | B | C | D | i
--
 
-- Timing: Normal mode Fast mode
142,433 → 142,376
 
library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
use ieee.std_logic_arith.all;
 
entity i2c_master_bit_ctrl is
port (
clk : in std_logic;
rst : in std_logic;
nReset : in std_logic;
ena : in std_logic; -- core enable signal
port (
clk : in std_logic;
rst : in std_logic;
nReset : in std_logic;
ena : in std_logic; -- core enable signal
 
clk_cnt : in unsigned(15 downto 0); -- clock prescale value
clk_cnt : in unsigned(15 downto 0); -- clock prescale value
 
cmd : in std_logic_vector(3 downto 0);
cmd_ack : out std_logic; -- command completed
busy : out std_logic; -- i2c bus busy
al : out std_logic; -- arbitration lost
cmd : in std_logic_vector(3 downto 0);
cmd_ack : out std_logic; -- command completed
busy : out std_logic; -- i2c bus busy
al : out std_logic; -- arbitration lost
 
din : in std_logic;
dout : out std_logic;
din : in std_logic;
dout : out std_logic;
 
-- i2c lines
scl_i : in std_logic; -- i2c clock line input
scl_o : out std_logic; -- i2c clock line output
scl_oen : out std_logic; -- i2c clock line output enable, active low
sda_i : in std_logic; -- i2c data line input
sda_o : out std_logic; -- i2c data line output
sda_oen : out std_logic -- i2c data line output enable, active low
);
-- i2c lines
scl_i : in std_logic; -- i2c clock line input
scl_o : out std_logic; -- i2c clock line output
scl_oen : out std_logic; -- i2c clock line output enable, active low
sda_i : in std_logic; -- i2c data line input
sda_o : out std_logic; -- i2c data line output
sda_oen : out std_logic -- i2c data line output enable, active low
);
end entity i2c_master_bit_ctrl;
 
architecture structural of i2c_master_bit_ctrl is
constant I2C_CMD_NOP : std_logic_vector(3 downto 0) := "0000";
constant I2C_CMD_START : std_logic_vector(3 downto 0) := "0001";
constant I2C_CMD_STOP : std_logic_vector(3 downto 0) := "0010";
constant I2C_CMD_READ : std_logic_vector(3 downto 0) := "0100";
constant I2C_CMD_WRITE : std_logic_vector(3 downto 0) := "1000";
constant I2C_CMD_NOP : std_logic_vector(3 downto 0) := "0000";
constant I2C_CMD_START : std_logic_vector(3 downto 0) := "0001";
constant I2C_CMD_STOP : std_logic_vector(3 downto 0) := "0010";
constant I2C_CMD_READ : std_logic_vector(3 downto 0) := "0100";
constant I2C_CMD_WRITE : std_logic_vector(3 downto 0) := "1000";
 
type states is (idle, start_a, start_b, start_c, start_d, start_e,
stop_a, stop_b, stop_c, stop_d, rd_a, rd_b, rd_c, rd_d, wr_a, wr_b, wr_c, wr_d);
signal c_state : states;
type states is (idle, start_a, start_b, start_c, start_d, start_e,
stop_a, stop_b, stop_c, stop_d, rd_a, rd_b, rd_c, rd_d, wr_a, wr_b, wr_c, wr_d);
signal c_state : states;
 
signal iscl_oen, isda_oen : std_logic; -- internal I2C lines
signal sda_chk : std_logic; -- check SDA status (multi-master arbitration)
signal dscl_oen : std_logic; -- delayed scl_oen signals
signal sSCL, sSDA : std_logic; -- synchronized SCL and SDA inputs
signal dSCL, dSDA : std_logic; -- delayed versions ofsSCL and sSDA
signal clk_en : std_logic; -- statemachine clock enable
signal scl_sync, slave_wait : std_logic; -- clock generation signals
signal ial : std_logic; -- internal arbitration lost signal
signal cnt : unsigned(15 downto 0); -- clock divider counter (synthesis)
signal iscl_oen, isda_oen : std_logic; -- internal I2C lines
signal sda_chk : std_logic; -- check SDA status (multi-master arbitration)
signal dscl_oen : std_logic; -- delayed scl_oen signals
signal sSCL, sSDA : std_logic; -- synchronized SCL and SDA inputs
signal dSCL, dSDA : std_logic; -- delayed versions ofsSCL and sSDA
signal clk_en : std_logic; -- statemachine clock enable
signal scl_sync, slave_wait : std_logic; -- clock generation signals
signal ial : std_logic; -- internal arbitration lost signal
-- signal cnt : unsigned(15 downto 0) := clk_cnt; -- clock divider counter (simulation)
signal cnt : unsigned(15 downto 0); -- clock divider counter (synthesis)
 
begin
-- whenever the slave is not ready it can delay the cycle by pulling SCL low
-- delay scl_oen
process (clk, nReset)
begin
if (nReset = '0') then
dscl_oen <= '0';
elsif (clk'event and clk = '1') then
dscl_oen <= iscl_oen;
end if;
end process;
-- whenever the slave is not ready it can delay the cycle by pulling SCL low
-- delay scl_oen
process (clk)
begin
if (clk'event and clk = '1') then
dscl_oen <= iscl_oen;
end if;
end process;
 
-- slave_wait is asserted when master wants to drive SCL high, but the slave pulls it low
-- slave_wait remains asserted until the slave releases SCL
process (clk, nReset)
begin
if (nReset = '0') then
slave_wait <= '0';
elsif (clk'event and clk = '1') then
slave_wait <= (iscl_oen and not dscl_oen and not sSCL) or (slave_wait and not sSCL);
end if;
end process;
-- slave_wait is asserted when master wants to drive SCL high, but the slave (another master) pulls it low
-- slave_wait remains asserted until the slave (other master) releases SCL
process (clk, nReset)
begin
if (nReset = '0') then
slave_wait <= '0';
elsif (clk'event and clk = '1') then
slave_wait <= (iscl_oen and not dscl_oen and not sSCL) or (slave_wait and not sSCL);
end if;
end process;
 
-- master drives SCL high, but another master pulls it low
-- master start counting down its low cycle now (clock synchronization)
scl_sync <= dSCL and not sSCL and iscl_oen;
-- master drives SCL high, but another master pulls it low
-- master start counting down its low cycle now (clock synchronization)
scl_sync <= dSCL and not sSCL and iscl_oen;
 
-- generate clk enable signal
gen_clken: process(clk, nReset)
begin
if (nReset = '0') then
cnt <= (others => '0');
clk_en <= '1';
elsif (clk'event and clk = '1') then
if ((rst = '1') or (cnt = 0) or (ena = '0') or (scl_sync = '1')) then
cnt <= clk_cnt;
clk_en <= '1';
elsif (slave_wait = '1') then
cnt <= cnt;
clk_en <= '0';
else
cnt <= cnt -1;
clk_en <= '0';
end if;
end if;
end process gen_clken;
-- generate clk enable signal
gen_clken: process(clk, nReset)
begin
if (nReset = '0') then
cnt <= (others => '0');
clk_en <= '1';
elsif (clk'event and clk = '1') then
if (rst = '1') then
cnt <= (others => '0');
clk_en <= '1';
elsif ( (cnt = 0) or (ena = '0') or (scl_sync = '1') ) then
cnt <= clk_cnt;
clk_en <= '1';
elsif (slave_wait = '1') then
cnt <= cnt;
clk_en <= '0';
else
cnt <= cnt -1;
clk_en <= '0';
end if;
end if;
end process gen_clken;
 
 
-- generate bus status controller
bus_status_ctrl: block
signal cSCL, cSDA : std_logic_vector( 1 downto 0); -- capture SDA and SCL
signal fSCL, fSDA : std_logic_vector( 2 downto 0); -- filter inputs for SCL and SDA
signal filter_cnt : unsigned(13 downto 0); -- clock divider for filter
signal sta_condition : std_logic; -- start detected
signal sto_condition : std_logic; -- stop detected
signal cmd_stop : std_logic; -- STOP command
signal ibusy : std_logic; -- internal busy signal
begin
-- capture SCL and SDA
capture_scl_sda: process(clk, nReset)
begin
if (nReset = '0') then
cSCL <= "00";
cSDA <= "00";
elsif (clk'event and clk = '1') then
if (rst = '1') then
cSCL <= "00";
cSDA <= "00";
else
cSCL <= (cSCL(0) & scl_i);
cSDA <= (cSDA(0) & sda_i);
end if;
end if;
end process capture_scl_sda;
-- generate bus status controller
bus_status_ctrl: block
signal sta_condition : std_logic; -- start detected
signal sto_condition : std_logic; -- stop detected
signal cmd_stop : std_logic; -- STOP command
signal ibusy : std_logic; -- internal busy signal
begin
-- synchronize SCL and SDA inputs
synch_scl_sda: process(clk, nReset)
begin
if (nReset = '0') then
sSCL <= '1';
sSDA <= '1';
 
-- filter SCL and SDA; (attempt to) remove glitches
filter_divider: process(clk, nReset)
begin
if (nReset = '0') then
filter_cnt <= (others => '0');
elsif (clk'event and clk = '1') then
if ((rst = '1') or (filter_cnt = 0)) then
filter_cnt <= clk_cnt(15 downto 2);
else
filter_cnt <= filter_cnt -1;
end if;
end if;
end process filter_divider;
dSCL <= '1';
dSDA <= '1';
elsif (clk'event and clk = '1') then
if (rst = '1') then
sSCL <= '1';
sSDA <= '1';
 
filter_scl_sda: process(clk, nReset)
begin
if (nReset = '0') then
fSCL <= (others => '1');
fSDA <= (others => '1');
elsif (clk'event and clk = '1') then
if (rst = '1') then
fSCL <= (others => '1');
fSDA <= (others => '1');
elsif (filter_cnt = 0) then
fSCL <= (fSCL(1 downto 0) & cSCL(1));
fSDA <= (fSDA(1 downto 0) & cSDA(1));
end if;
end if;
end process filter_scl_sda;
dSCL <= '1';
dSDA <= '1';
else
sSCL <= scl_i;
sSDA <= sda_i;
 
-- generate filtered SCL and SDA signals
scl_sda: process(clk, nReset)
begin
if (nReset = '0') then
sSCL <= '1';
sSDA <= '1';
dSCL <= sSCL;
dSDA <= sSDA;
end if;
end if;
end process synch_SCL_SDA;
 
dSCL <= '1';
dSDA <= '1';
elsif (clk'event and clk = '1') then
if (rst = '1') then
sSCL <= '1';
sSDA <= '1';
-- detect start condition => detect falling edge on SDA while SCL is high
-- detect stop condition => detect rising edge on SDA while SCL is high
detect_sta_sto: process(clk, nReset)
begin
if (nReset = '0') then
sta_condition <= '0';
sto_condition <= '0';
elsif (clk'event and clk = '1') then
if (rst = '1') then
sta_condition <= '0';
sto_condition <= '0';
else
sta_condition <= (not sSDA and dSDA) and sSCL;
sto_condition <= (sSDA and not dSDA) and sSCL;
end if;
end if;
end process detect_sta_sto;
 
dSCL <= '1';
dSDA <= '1';
else
sSCL <= (fSCL(2) and fSCL(1)) or
(fSCL(2) and fSCL(0)) or
(fSCL(1) and fSCL(0));
sSDA <= (fSDA(2) and fSDA(1)) or
(fSDA(2) and fSDA(0)) or
(fSCL(1) and fSCL(0));
-- generate i2c-bus busy signal
gen_busy: process(clk, nReset)
begin
if (nReset = '0') then
ibusy <= '0';
elsif (clk'event and clk = '1') then
if (rst = '1') then
ibusy <= '0';
else
ibusy <= (sta_condition or ibusy) and not sto_condition;
end if;
end if;
end process gen_busy;
busy <= ibusy;
 
dSCL <= sSCL;
dSDA <= sSDA;
end if;
end if;
end process scl_sda;
 
-- generate arbitration lost signal
-- aribitration lost when:
-- 1) master drives SDA high, but the i2c bus is low
-- 2) stop detected while not requested (detect during 'idle' state)
gen_al: process(clk, nReset)
begin
if (nReset = '0') then
cmd_stop <= '0';
ial <= '0';
elsif (clk'event and clk = '1') then
if (rst = '1') then
cmd_stop <= '0';
ial <= '0';
else
if (clk_en = '1') then
if (cmd = I2C_CMD_STOP) then
cmd_stop <= '1';
else
cmd_stop <= '0';
end if;
end if;
 
-- detect start condition => detect falling edge on SDA while SCL is high
-- detect stop condition => detect rising edge on SDA while SCL is high
detect_sta_sto: process(clk, nReset)
begin
if (nReset = '0') then
sta_condition <= '0';
sto_condition <= '0';
elsif (clk'event and clk = '1') then
if (rst = '1') then
sta_condition <= '0';
sto_condition <= '0';
else
sta_condition <= (not sSDA and dSDA) and sSCL;
sto_condition <= (sSDA and not dSDA) and sSCL;
end if;
end if;
end process detect_sta_sto;
if (c_state = idle) then
ial <= (sda_chk and not sSDA and isda_oen);
else
ial <= (sda_chk and not sSDA and isda_oen) or (sto_condition and not cmd_stop);
end if;
 
end if;
end if;
end process gen_al;
al <= ial;
 
-- generate i2c-bus busy signal
gen_busy: process(clk, nReset)
begin
if (nReset = '0') then
ibusy <= '0';
elsif (clk'event and clk = '1') then
if (rst = '1') then
ibusy <= '0';
else
ibusy <= (sta_condition or ibusy) and not sto_condition;
end if;
end if;
end process gen_busy;
busy <= ibusy;
-- generate dout signal, store dout on rising edge of SCL
gen_dout: process(clk)
begin
if (clk'event and clk = '1') then
if (sSCL = '1' and dSCL = '0') then
dout <= sSDA;
end if;
end if;
end process gen_dout;
end block bus_status_ctrl;
 
 
-- generate arbitration lost signal
-- aribitration lost when:
-- 1) master drives SDA high, but the i2c bus is low
-- 2) stop detected while not requested (detect during 'idle' state)
gen_al: process(clk, nReset)
begin
if (nReset = '0') then
cmd_stop <= '0';
ial <= '0';
elsif (clk'event and clk = '1') then
if (rst = '1') then
cmd_stop <= '0';
ial <= '0';
else
if (clk_en = '1') then
if (cmd = I2C_CMD_STOP) then
cmd_stop <= '1';
else
cmd_stop <= '0';
end if;
end if;
-- generate statemachine
nxt_state_decoder : process (clk, nReset, c_state, cmd)
begin
if (nReset = '0') then
c_state <= idle;
cmd_ack <= '0';
iscl_oen <= '1';
isda_oen <= '1';
sda_chk <= '0';
elsif (clk'event and clk = '1') then
if (rst = '1' or ial = '1') then
c_state <= idle;
cmd_ack <= '0';
iscl_oen <= '1';
isda_oen <= '1';
sda_chk <= '0';
else
cmd_ack <= '0'; -- default no acknowledge
 
if (c_state = idle) then
ial <= (sda_chk and not sSDA and isda_oen) or (sto_condition and not cmd_stop);
else
ial <= (sda_chk and not sSDA and isda_oen);
end if;
end if;
end if;
end process gen_al;
al <= ial;
if (clk_en = '1') then
case (c_state) is
-- idle
when idle =>
case cmd is
when I2C_CMD_START => c_state <= start_a;
when I2C_CMD_STOP => c_state <= stop_a;
when I2C_CMD_WRITE => c_state <= wr_a;
when I2C_CMD_READ => c_state <= rd_a;
when others => c_state <= idle; -- NOP command
end case;
 
iscl_oen <= iscl_oen; -- keep SCL in same state
isda_oen <= isda_oen; -- keep SDA in same state
sda_chk <= '0'; -- don't check SDA
 
-- generate dout signal, store dout on rising edge of SCL
gen_dout: process(clk, nReset)
begin
if (nReset = '0') then
dout <= '0';
elsif (clk'event and clk = '1') then
if (sSCL = '1' and dSCL = '0') then
dout <= sSDA;
end if;
end if;
end process gen_dout;
end block bus_status_ctrl;
-- start
when start_a =>
c_state <= start_b;
iscl_oen <= iscl_oen; -- keep SCL in same state (for repeated start)
isda_oen <= '1'; -- set SDA high
sda_chk <= '0'; -- don't check SDA
 
when start_b =>
c_state <= start_c;
iscl_oen <= '1'; -- set SCL high
isda_oen <= '1'; -- keep SDA high
sda_chk <= '0'; -- don't check SDA
 
-- generate statemachine
nxt_state_decoder : process (clk, nReset)
begin
if (nReset = '0') then
c_state <= idle;
cmd_ack <= '0';
iscl_oen <= '1';
isda_oen <= '1';
sda_chk <= '0';
elsif (clk'event and clk = '1') then
if (rst = '1' or ial = '1') then
c_state <= idle;
cmd_ack <= '0';
iscl_oen <= '1';
isda_oen <= '1';
sda_chk <= '0';
else
cmd_ack <= '0'; -- default no acknowledge
when start_c =>
c_state <= start_d;
iscl_oen <= '1'; -- keep SCL high
isda_oen <= '0'; -- set SDA low
sda_chk <= '0'; -- don't check SDA
 
if (clk_en = '1') then
case (c_state) is
-- idle
when idle =>
case cmd is
when I2C_CMD_START => c_state <= start_a;
when I2C_CMD_STOP => c_state <= stop_a;
when I2C_CMD_WRITE => c_state <= wr_a;
when I2C_CMD_READ => c_state <= rd_a;
when others => c_state <= idle; -- NOP command
end case;
when start_d =>
c_state <= start_e;
iscl_oen <= '1'; -- keep SCL high
isda_oen <= '0'; -- keep SDA low
sda_chk <= '0'; -- don't check SDA
 
iscl_oen <= iscl_oen; -- keep SCL in same state
isda_oen <= isda_oen; -- keep SDA in same state
sda_chk <= '0'; -- don't check SDA
when start_e =>
c_state <= idle;
cmd_ack <= '1'; -- command completed
iscl_oen <= '0'; -- set SCL low
isda_oen <= '0'; -- keep SDA low
sda_chk <= '0'; -- don't check SDA
 
-- start
when start_a =>
c_state <= start_b;
iscl_oen <= iscl_oen; -- keep SCL in same state (for repeated start)
isda_oen <= '1'; -- set SDA high
sda_chk <= '0'; -- don't check SDA
-- stop
when stop_a =>
c_state <= stop_b;
iscl_oen <= '0'; -- keep SCL low
isda_oen <= '0'; -- set SDA low
sda_chk <= '0'; -- don't check SDA
 
when start_b =>
c_state <= start_c;
iscl_oen <= '1'; -- set SCL high
isda_oen <= '1'; -- keep SDA high
sda_chk <= '0'; -- don't check SDA
when stop_b =>
c_state <= stop_c;
iscl_oen <= '1'; -- set SCL high
isda_oen <= '0'; -- keep SDA low
sda_chk <= '0'; -- don't check SDA
 
when start_c =>
c_state <= start_d;
iscl_oen <= '1'; -- keep SCL high
isda_oen <= '0'; -- set SDA low
sda_chk <= '0'; -- don't check SDA
when stop_c =>
c_state <= stop_d;
iscl_oen <= '1'; -- keep SCL high
isda_oen <= '0'; -- keep SDA low
sda_chk <= '0'; -- don't check SDA
 
when start_d =>
c_state <= start_e;
iscl_oen <= '1'; -- keep SCL high
isda_oen <= '0'; -- keep SDA low
sda_chk <= '0'; -- don't check SDA
when stop_d =>
c_state <= idle;
cmd_ack <= '1'; -- command completed
iscl_oen <= '1'; -- keep SCL high
isda_oen <= '1'; -- set SDA high
sda_chk <= '0'; -- don't check SDA
 
when start_e =>
c_state <= idle;
cmd_ack <= '1'; -- command completed
iscl_oen <= '0'; -- set SCL low
isda_oen <= '0'; -- keep SDA low
sda_chk <= '0'; -- don't check SDA
-- read
when rd_a =>
c_state <= rd_b;
iscl_oen <= '0'; -- keep SCL low
isda_oen <= '1'; -- tri-state SDA
sda_chk <= '0'; -- don't check SDA
 
-- stop
when stop_a =>
c_state <= stop_b;
iscl_oen <= '0'; -- keep SCL low
isda_oen <= '0'; -- set SDA low
sda_chk <= '0'; -- don't check SDA
when rd_b =>
c_state <= rd_c;
iscl_oen <= '1'; -- set SCL high
isda_oen <= '1'; -- tri-state SDA
sda_chk <= '0'; -- don't check SDA
 
when stop_b =>
c_state <= stop_c;
iscl_oen <= '1'; -- set SCL high
isda_oen <= '0'; -- keep SDA low
sda_chk <= '0'; -- don't check SDA
when rd_c =>
c_state <= rd_d;
iscl_oen <= '1'; -- keep SCL high
isda_oen <= '1'; -- tri-state SDA
sda_chk <= '0'; -- don't check SDA
 
when stop_c =>
c_state <= stop_d;
iscl_oen <= '1'; -- keep SCL high
isda_oen <= '0'; -- keep SDA low
sda_chk <= '0'; -- don't check SDA
when rd_d =>
c_state <= idle;
cmd_ack <= '1'; -- command completed
iscl_oen <= '0'; -- set SCL low
isda_oen <= '1'; -- tri-state SDA
sda_chk <= '0'; -- don't check SDA
 
when stop_d =>
c_state <= idle;
cmd_ack <= '1'; -- command completed
iscl_oen <= '1'; -- keep SCL high
isda_oen <= '1'; -- set SDA high
sda_chk <= '0'; -- don't check SDA
-- write
when wr_a =>
c_state <= wr_b;
iscl_oen <= '0'; -- keep SCL low
isda_oen <= din; -- set SDA
sda_chk <= '0'; -- don't check SDA (SCL low)
 
-- read
when rd_a =>
c_state <= rd_b;
iscl_oen <= '0'; -- keep SCL low
isda_oen <= '1'; -- tri-state SDA
sda_chk <= '0'; -- don't check SDA
when wr_b =>
c_state <= wr_c;
iscl_oen <= '1'; -- set SCL high
isda_oen <= din; -- keep SDA
sda_chk <= '1'; -- check SDA
 
when rd_b =>
c_state <= rd_c;
iscl_oen <= '1'; -- set SCL high
isda_oen <= '1'; -- tri-state SDA
sda_chk <= '0'; -- don't check SDA
when wr_c =>
c_state <= wr_d;
iscl_oen <= '1'; -- keep SCL high
isda_oen <= din; -- keep SDA
sda_chk <= '1'; -- check SDA
 
when rd_c =>
c_state <= rd_d;
iscl_oen <= '1'; -- keep SCL high
isda_oen <= '1'; -- tri-state SDA
sda_chk <= '0'; -- don't check SDA
when wr_d =>
c_state <= idle;
cmd_ack <= '1'; -- command completed
iscl_oen <= '0'; -- set SCL low
isda_oen <= din; -- keep SDA
sda_chk <= '0'; -- don't check SDA (SCL low)
 
when rd_d =>
c_state <= idle;
cmd_ack <= '1'; -- command completed
iscl_oen <= '0'; -- set SCL low
isda_oen <= '1'; -- tri-state SDA
sda_chk <= '0'; -- don't check SDA
when others =>
 
-- write
when wr_a =>
c_state <= wr_b;
iscl_oen <= '0'; -- keep SCL low
isda_oen <= din; -- set SDA
sda_chk <= '0'; -- don't check SDA (SCL low)
end case;
end if;
end if;
end if;
end process nxt_state_decoder;
 
when wr_b =>
c_state <= wr_c;
iscl_oen <= '1'; -- set SCL high
isda_oen <= din; -- keep SDA
sda_chk <= '0'; -- don't check SDA yet
-- Allow some more time for SDA and SCL to settle
 
when wr_c =>
c_state <= wr_d;
iscl_oen <= '1'; -- keep SCL high
isda_oen <= din; -- keep SDA
sda_chk <= '1'; -- check SDA
 
when wr_d =>
c_state <= idle;
cmd_ack <= '1'; -- command completed
iscl_oen <= '0'; -- set SCL low
isda_oen <= din; -- keep SDA
sda_chk <= '0'; -- don't check SDA (SCL low)
 
when others =>
 
end case;
end if;
end if;
end if;
end process nxt_state_decoder;
 
 
-- assign outputs
scl_o <= '0';
scl_oen <= iscl_oen;
sda_o <= '0';
sda_oen <= isda_oen;
-- assign outputs
scl_o <= '0';
scl_oen <= iscl_oen;
sda_o <= '0';
sda_oen <= isda_oen;
end architecture structural;
 

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