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# SPI Master Lightweight
Taken from [OpenCores](https://opencores.org/projects/spi_master_lightweight).

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library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity lw_spi_master is
generic (
c_clkfreq : integer := 50_000_000;
c_sclkfreq : integer := 5_000_000;
c_cpol : std_logic := '0';
c_cpha : std_logic := '0'
);
Port (
clk_i : in STD_LOGIC;
rst_i : in STD_LOGIC;
en_i : in STD_LOGIC;
mosi_data_i : in STD_LOGIC_VECTOR (7 downto 0);
miso_data_o : out STD_LOGIC_VECTOR (7 downto 0);
data_ready_o : out STD_LOGIC;
cs_o : out STD_LOGIC;
sclk_o : out STD_LOGIC;
mosi_o : out STD_LOGIC;
miso_i : in STD_LOGIC
);
end lw_spi_master;
architecture Behavioral of lw_spi_master is
signal write_reg : std_logic_vector (7 downto 0) := (others => '0');
signal read_reg : std_logic_vector (7 downto 0) := (others => '0');
signal sclk_en : std_logic := '0';
signal sclk : std_logic := '0';
signal sclk_prev : std_logic := '0';
signal sclk_rise : std_logic := '0';
signal sclk_fall : std_logic := '0';
signal pol_phase : std_logic_vector (1 downto 0) := (others => '0');
signal mosi_en : std_logic := '0';
signal miso_en : std_logic := '0';
constant c_edgecntrlimdiv2 : integer := c_clkfreq/(c_sclkfreq*2);
signal edgecntr : integer range 0 to c_edgecntrlimdiv2 := 0;
signal cntr : integer range 0 to 15 := 0;
type states is (S_IDLE, S_TRANSFER);
signal state : states := S_IDLE;
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
begin
pol_phase <= c_cpol & c_cpha;
P_SAMPLE_EN : process (pol_phase, sclk_fall, sclk_rise) begin
case pol_phase is
when "00" =>
mosi_en <= sclk_fall;
miso_en <= sclk_rise;
when "01" =>
mosi_en <= sclk_rise;
miso_en <= sclk_fall;
when "10" =>
mosi_en <= sclk_rise;
miso_en <= sclk_fall;
when "11" =>
mosi_en <= sclk_fall;
miso_en <= sclk_rise;
when others =>
end case;
end process;
P_RISEFALL_DETECT : process (sclk, sclk_prev) begin
if (sclk = '1' and sclk_prev = '0') then
sclk_rise <= '1';
else
sclk_rise <= '0';
end if;
if (sclk = '0' and sclk_prev = '1') then
sclk_fall <= '1';
else
sclk_fall <= '0';
end if;
end process;
P_MAIN : process (clk_i) begin
if (rising_edge(clk_i)) then
if rst_i = '1' then
cs_o <= '1';
mosi_o <= '0';
data_ready_o <= '0';
sclk_en <= '0';
else
sclk_prev <= sclk;
case state is
when S_IDLE =>
cs_o <= '1';
mosi_o <= '0';
data_ready_o <= '0';
sclk_en <= '0';
cntr <= 0;
if (c_cpol = '0') then
sclk_o <= '0';
else
sclk_o <= '1';
end if;
if (en_i = '1') then
state <= S_TRANSFER;
sclk_en <= '1';
write_reg <= mosi_data_i;
mosi_o <= mosi_data_i(7);
read_reg <= x"00";
end if;
when S_TRANSFER =>
cs_o <= '0';
mosi_o <= write_reg(7);
if (c_cpha = '1') then
if (cntr = 0) then
sclk_o <= sclk;
if (miso_en = '1') then
read_reg(0) <= miso_i;
read_reg(7 downto 1) <= read_reg(6 downto 0);
cntr <= cntr + 1;
end if;
elsif (cntr = 8) then
data_ready_o <= '1';
miso_data_o <= read_reg;
if (mosi_en = '1') then
data_ready_o <= '0';
if (en_i = '1') then
write_reg <= mosi_data_i;
mosi_o <= mosi_data_i(7);
sclk_o <= sclk;
cntr <= 0;
else
state <= S_IDLE;
cs_o <= '1';
end if;
end if;
elsif (cntr = 9) then
if (miso_en = '1') then
state <= S_IDLE;
cs_o <= '1';
end if;
else
sclk_o <= sclk;
if (miso_en = '1') then
read_reg(0) <= miso_i;
read_reg(7 downto 1) <= read_reg(6 downto 0);
cntr <= cntr + 1;
end if;
if (mosi_en = '1') then
mosi_o <= write_reg(7);
write_reg(7 downto 1) <= write_reg(6 downto 0);
end if;
end if;
else -- c_cpha = '0'
if (cntr = 0) then
sclk_o <= sclk;
if (miso_en = '1') then
read_reg(0) <= miso_i;
read_reg(7 downto 1) <= read_reg(6 downto 0);
cntr <= cntr + 1;
end if;
elsif (cntr = 8) then
data_ready_o <= '1';
miso_data_o <= read_reg;
sclk_o <= sclk;
if (mosi_en = '1') then
data_ready_o <= '0';
if (en_i = '1') then
write_reg <= mosi_data_i;
mosi_o <= mosi_data_i(7);
cntr <= 0;
else
cntr <= cntr + 1;
end if;
if (miso_en = '1') then
state <= S_IDLE;
cs_o <= '1';
end if;
end if;
elsif (cntr = 9) then
if (miso_en = '1') then
state <= S_IDLE;
cs_o <= '1';
end if;
else
sclk_o <= sclk;
if (miso_en = '1') then
read_reg(0) <= miso_i;
read_reg(7 downto 1) <= read_reg(6 downto 0);
cntr <= cntr + 1;
end if;
if (mosi_en = '1') then
write_reg(7 downto 1) <= write_reg(6 downto 0);
end if;
end if;
end if;
end case;
end if;
end if;
end process;
P_SCLK_GEN : process (clk_i) begin
if (rising_edge(clk_i)) then
if (sclk_en = '1') then
if edgecntr = c_edgecntrlimdiv2-1 then
sclk <= not sclk;
edgecntr <= 0;
else
edgecntr <= edgecntr + 1;
end if;
else
edgecntr <= 0;
if (c_cpol = '0') then
sclk <= '0';
else
sclk <= '1';
end if;
end if;
end if;
end process;
end Behavioral;

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--------------------------------------------------------------------------------
-- AUTHOR: MEHMET BURAK AYKENAR
-- CREATED: 09.12.2019
-- REVISION DATE: 09.12.2019
--
--------------------------------------------------------------------------------
-- DESCRIPTION:
-- This module implements master part of SPI communication interface and can be used to any SPI slave IC.
-- In order to read from a slave IC, mosi_data_i input signal should be assigned to desired value and en_i signal should be high.
-- In order to write to a slave IC, en_i input signal should be high.
-- data_ready_o output signal has the logic high value for one clock cycle as read or/and write operation finished. miso_data_o output signal
-- has the data read from slave IC.
-- In order to read or/and write consecutively, en_i signal should be kept high. To end the transaction, en_i input signal should be assigned to zero
-- when data_ready_o output signal gets high.
--------------------------------------------------------------------------------
-- Limitation/Assumption: In order to use this module properly, the ratio of (c_clkfreq / c_sclkFreq) should be equal to 8 or more.
-- For higher SCLK frequencies are possible but more elaboration is needed.
-- Notes: c_cpol and c_cpha parameters are clock polarity and clock phase, respectively.
--------------------------------------------------------------------------------
-- VHDL DIALECT: VHDL '93
--
--------------------------------------------------------------------------------
-- PROJECT : General purpose
-- BOARD : General purpose
-- ENTITY : spi_master
--------------------------------------------------------------------
-- FILE : spi_master.vhd
--------------------------------------------------------------------------------
-- REVISION HISTORY:
-- REVISION DATE AUTHOR COMMENT
-- -------- ---------- ------------ -----------
-- 1.0 19.12.2019 M.B.AYKENAR INITIAL REVISION
--------------------------------------------------------------------------------
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity spi_master is
generic (
c_clkfreq : integer := 50_000_000;
c_sclkfreq : integer := 1_000_000;
c_cpol : std_logic := '0';
c_cpha : std_logic := '0'
);
Port (
clk_i : in STD_LOGIC;
en_i : in STD_LOGIC;
mosi_data_i : in STD_LOGIC_VECTOR (7 downto 0);
miso_data_o : out STD_LOGIC_VECTOR (7 downto 0);
data_ready_o : out STD_LOGIC;
cs_o : out STD_LOGIC;
sclk_o : out STD_LOGIC;
mosi_o : out STD_LOGIC;
miso_i : in STD_LOGIC
);
end spi_master;
architecture Behavioral of spi_master is
--------------------------------------------------------------------------------
-- CONSTANTS
constant c_edgecntrlimdiv2 : integer := c_clkfreq/(c_sclkfreq*2);
--------------------------------------------------------------------------------
-- INTERNAL SIGNALS
signal write_reg : std_logic_vector (7 downto 0) := (others => '0');
signal read_reg : std_logic_vector (7 downto 0) := (others => '0');
signal sclk_en : std_logic := '0';
signal sclk : std_logic := '0';
signal sclk_prev : std_logic := '0';
signal sclk_rise : std_logic := '0';
signal sclk_fall : std_logic := '0';
signal pol_phase : std_logic_vector (1 downto 0) := (others => '0');
signal mosi_en : std_logic := '0';
signal miso_en : std_logic := '0';
signal once : std_logic := '0';
signal edgecntr : integer range 0 to c_edgecntrlimdiv2 := 0;
signal cntr : integer range 0 to 15 := 0;
--------------------------------------------------------------------------------
-- STATE DEFINITIONS
type states is (S_IDLE, S_TRANSFER);
signal state : states := S_IDLE;
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
begin
pol_phase <= c_cpol & c_cpha;
--------------------------------------------------------------------------------
-- SAMPLE_EN process assigns mosi_en and miso_en internal signals to sclk_fall or sclk_rise in a combinational logic according to
-- generic parameters of c_cpol and c_cpha via pol_phase signal.
P_SAMPLE_EN : process (pol_phase, sclk_fall, sclk_rise) begin
case pol_phase is
when "00" =>
mosi_en <= sclk_fall;
miso_en <= sclk_rise;
when "01" =>
mosi_en <= sclk_rise;
miso_en <= sclk_fall;
when "10" =>
mosi_en <= sclk_rise;
miso_en <= sclk_fall;
when "11" =>
mosi_en <= sclk_fall;
miso_en <= sclk_rise;
when others =>
end case;
end process P_SAMPLE_EN;
--------------------------------------------------------------------------------
-- RISEFALL_DETECT process assigns sclk_rise and sclk_fall signals in a combinational logic.
P_RISEFALL_DETECT : process (sclk, sclk_prev) begin
if (sclk = '1' and sclk_prev = '0') then
sclk_rise <= '1';
else
sclk_rise <= '0';
end if;
if (sclk = '0' and sclk_prev = '1') then
sclk_fall <= '1';
else
sclk_fall <= '0';
end if;
end process P_RISEFALL_DETECT;
--------------------------------------------------------------------------------
-- In the MAIN process S_IDLE and S_TRANSFER states are implemented. state changes from S_IDLE to S_TRANSFER when en_i input
-- signal has the logic high value. At that cycle, write_reg signal is assigned to mosi_data_i input signal. According to c_cpha generic
-- parameter, the transaction operation changes slightly. This operational difference is well explained in the paper that can be found
-- in Documents folder of the SPI, which is located in SVN server.
P_MAIN : process (clk_i) begin
if (rising_edge(clk_i)) then
data_ready_o <= '0';
sclk_prev <= sclk;
case state is
--------------------------------------------------------------------------------
when S_IDLE =>
cs_o <= '1';
mosi_o <= '0';
data_ready_o <= '0';
sclk_en <= '0';
cntr <= 0;
if (c_cpol = '0') then
sclk_o <= '0';
else
sclk_o <= '1';
end if;
if (en_i = '1') then
state <= S_TRANSFER;
sclk_en <= '1';
write_reg <= mosi_data_i;
mosi_o <= mosi_data_i(7);
read_reg <= x"00";
end if;
--------------------------------------------------------------------------------
when S_TRANSFER =>
cs_o <= '0';
mosi_o <= write_reg(7);
if (c_cpha = '1') then
if (cntr = 0) then
sclk_o <= sclk;
if (miso_en = '1') then
read_reg(0) <= miso_i;
read_reg(7 downto 1) <= read_reg(6 downto 0);
cntr <= cntr + 1;
once <= '1';
end if;
elsif (cntr = 8) then
if (once = '1') then
data_ready_o <= '1';
once <= '0';
end if;
miso_data_o <= read_reg;
if (mosi_en = '1') then
if (en_i = '1') then
write_reg <= mosi_data_i;
mosi_o <= mosi_data_i(7);
sclk_o <= sclk;
cntr <= 0;
else
state <= S_IDLE;
cs_o <= '1';
end if;
end if;
elsif (cntr = 9) then
if (miso_en = '1') then
state <= S_IDLE;
cs_o <= '1';
end if;
else
sclk_o <= sclk;
if (miso_en = '1') then
read_reg(0) <= miso_i;
read_reg(7 downto 1) <= read_reg(6 downto 0);
cntr <= cntr + 1;
end if;
if (mosi_en = '1') then
mosi_o <= write_reg(7);
write_reg(7 downto 1) <= write_reg(6 downto 0);
end if;
end if;
else -- c_cpha = '0'
if (cntr = 0) then
sclk_o <= sclk;
if (miso_en = '1') then
read_reg(0) <= miso_i;
read_reg(7 downto 1) <= read_reg(6 downto 0);
cntr <= cntr + 1;
once <= '1';
end if;
elsif (cntr = 8) then
if (once = '1') then
data_ready_o <= '1';
once <= '0';
end if;
miso_data_o <= read_reg;
sclk_o <= sclk;
if (mosi_en = '1') then
if (en_i = '1') then
write_reg <= mosi_data_i;
mosi_o <= mosi_data_i(7);
cntr <= 0;
else
cntr <= cntr + 1;
end if;
if (miso_en = '1') then
state <= S_IDLE;
cs_o <= '1';
end if;
end if;
elsif (cntr = 9) then
if (miso_en = '1') then
state <= S_IDLE;
cs_o <= '1';
end if;
else
sclk_o <= sclk;
if (miso_en = '1') then
read_reg(0) <= miso_i;
read_reg(7 downto 1) <= read_reg(6 downto 0);
cntr <= cntr + 1;
end if;
if (mosi_en = '1') then
write_reg(7 downto 1) <= write_reg(6 downto 0);
end if;
end if;
end if;
end case;
end if;
end process P_MAIN;
--------------------------------------------------------------------------------
-- In the SCLK_GEN process, internal sclk signal is generated if sclk_en signal is '1'.
P_SCLK_GEN : process (clk_i) begin
if (rising_edge(clk_i)) then
if (sclk_en = '1') then
if edgecntr = c_edgecntrlimdiv2-1 then
sclk <= not sclk;
edgecntr <= 0;
else
edgecntr <= edgecntr + 1;
end if;
else
edgecntr <= 0;
if (c_cpol = '0') then
sclk <= '0';
else
sclk <= '1';
end if;
end if;
end if;
end process P_SCLK_GEN;
end Behavioral;

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LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
ENTITY tb_lw_spi_master IS
END tb_lw_spi_master;
ARCHITECTURE behavior OF tb_lw_spi_master IS
-- Component Declaration for the Unit Under Test (UUT)
COMPONENT lw_spi_master
PORT(
clk_i : IN std_logic;
en_i : IN std_logic;
mosi_data_i : IN std_logic_vector(7 downto 0);
miso_data_o : OUT std_logic_vector(7 downto 0);
data_ready_o : OUT std_logic;
cs_o : OUT std_logic;
sclk_o : OUT std_logic;
mosi_o : OUT std_logic;
miso_i : IN std_logic
);
END COMPONENT;
--Inputs
signal clk_i : std_logic := '0';
signal en_i : std_logic := '0';
signal mosi_data_i : std_logic_vector(7 downto 0) := (others => '0');
signal miso_i : std_logic := '0';
--Outputs
signal miso_data_o : std_logic_vector(7 downto 0);
signal data_ready_o : std_logic;
signal cs_o : std_logic;
signal sclk_o : std_logic;
signal mosi_o : std_logic;
-- Clock period definitions
-- Clock period definitions
constant clk_i_period : time := 20 ns;
constant sckPeriod : time := 200 ns;
signal SPISIGNAL : std_logic_vector(7 downto 0) := (others => '0');
signal spiWrite : std_logic := '0';
signal spiWriteDone : std_logic := '0';
BEGIN
-- Instantiate the Unit Under Test (UUT)
uut: lw_spi_master PORT MAP (
clk_i => clk_i,
en_i => en_i,
mosi_data_i => mosi_data_i,
miso_data_o => miso_data_o,
data_ready_o => data_ready_o,
cs_o => cs_o,
sclk_o => sclk_o,
mosi_o => mosi_o,
miso_i => miso_i
);
-- Clock process definitions
clk_i_process :process
begin
clk_i <= '0';
wait for clk_i_period/2;
clk_i <= '1';
wait for clk_i_period/2;
end process;
SPIWRITE_P : process begin
wait until rising_edge(spiWrite);
-- for cpol = 1 cpha = 1
-- for cpol = 0 cpha = 0
miso_i <= SPISIGNAL(7);
wait until falling_edge(sclk_o);
miso_i <= SPISIGNAL(6);
wait until falling_edge(sclk_o);
miso_i <= SPISIGNAL(5);
wait until falling_edge(sclk_o);
miso_i <= SPISIGNAL(4);
wait until falling_edge(sclk_o);
miso_i <= SPISIGNAL(3);
wait until falling_edge(sclk_o);
miso_i <= SPISIGNAL(2);
wait until falling_edge(sclk_o);
miso_i <= SPISIGNAL(1);
wait until falling_edge(sclk_o);
miso_i <= SPISIGNAL(0);
-- for cpol = 0 cpha = 1
-- for cpol = 1 cpha = 0
-- miso_i <= SPISIGNAL(7);
-- wait until rising_edge(sclk_o);
-- miso_i <= SPISIGNAL(6);
-- wait until rising_edge(sclk_o);
-- miso_i <= SPISIGNAL(5);
-- wait until rising_edge(sclk_o);
-- miso_i <= SPISIGNAL(4);
-- wait until rising_edge(sclk_o);
-- miso_i <= SPISIGNAL(3);
-- wait until rising_edge(sclk_o);
-- miso_i <= SPISIGNAL(2);
-- wait until rising_edge(sclk_o);
-- miso_i <= SPISIGNAL(1);
-- wait until rising_edge(sclk_o);
-- miso_i <= SPISIGNAL(0);
spiWriteDone <= '1';
wait for 1 ps;
spiWriteDone <= '0';
end process;
-- Stimulus process
stim_proc: process
begin
-- hold reset state for 100 ns.
wait for 100 ns;
wait for clk_i_period*10;
-- insert stimulus here
----------------------------------------------------------------
-- -- CPOL,CPHA = 00
en_i <= '1';
-- write 0xA7, read 0xB2
mosi_data_i <= x"A7";
wait until falling_edge(cs_o);
SPISIGNAL <= x"B2";
spiWrite <= '1';
wait until rising_edge(spiWriteDone);
spiWrite <= '0';
-- write 0xB8, read 0xC3
wait until rising_edge(data_ready_o);
mosi_data_i <= x"B8";
wait until falling_edge(data_ready_o);
SPISIGNAL <= x"C3";
spiWrite <= '1';
wait until rising_edge(spiWriteDone);
spiWrite <= '0';
en_i <= '0';
----------------------------------------------------------------
-- -- CPOL,CPHA = 10
-- en_i <= '1';
--
-- -- write 0xA7, read 0xB2
-- mosi_data_i <= x"A7";
-- wait until falling_edge(cs_o);
-- wait for 50 ns;
-- SPISIGNAL <= x"B2";
-- spiWrite <= '1';
-- wait until rising_edge(spiWriteDone);
-- spiWrite <= '0';
--
-- -- write 0xB8, read 0xC3
-- wait until rising_edge(data_ready_o);
-- mosi_data_i <= x"B8";
-- wait until falling_edge(data_ready_o);
-- SPISIGNAL <= x"C3";
-- spiWrite <= '1';
-- wait until rising_edge(spiWriteDone);
-- spiWrite <= '0';
-- en_i <= '0';
----------------------------------------------------------------
-- CPOL,CPHA = 01
-- en_i <= '1';
--
-- -- write 0xA7, read 0xB2
-- mosi_data_i <= x"A7";
-- wait until falling_edge(cs_o);
-- wait until rising_edge(sclk_o);
-- SPISIGNAL <= x"B2";
-- spiWrite <= '1';
-- wait until rising_edge(spiWriteDone);
-- spiWrite <= '0';
--
-- -- write 0xB8, read 0xC3
-- wait until rising_edge(data_ready_o);
-- mosi_data_i <= x"B8";
-- wait until rising_edge(sclk_o);
-- SPISIGNAL <= x"C3";
-- spiWrite <= '1';
-- wait until rising_edge(spiWriteDone);
-- spiWrite <= '0';
-- en_i <= '0';
----------------------------------------------------------------
-- -- CPOL,CPHA = 11
-- en_i <= '1';
--
-- -- write 0xA7, read 0xB2
-- mosi_data_i <= x"A7";
-- wait until falling_edge(cs_o);
-- wait until falling_edge(sclk_o);
-- SPISIGNAL <= x"B2";
-- spiWrite <= '1';
-- wait until rising_edge(spiWriteDone);
-- spiWrite <= '0';
--
-- -- write 0xB8, read 0xC3
-- wait until rising_edge(data_ready_o);
-- mosi_data_i <= x"B8";
-- wait until falling_edge(sclk_o);
-- SPISIGNAL <= x"C3";
-- spiWrite <= '1';
-- wait until rising_edge(spiWriteDone);
-- spiWrite <= '0';
-- en_i <= '0';
wait for 1 us;
assert false
report "SIM DONE"
severity failure;
end process;
END;