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/rtl/spi_master.vhd
0,0 → 1,315
--------------------------------------------------------------------------------
-- 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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