source: firmware/FAD/FACT_FAD_lib/hdl/phase_shifter.vhd

-- 
-- phase_shifter.vhd
-- 
-- implements interface between w5300_modul.vhd 
-- and clock_generator_variable_PS_struct.vhd 
-- 
library ieee;
use ieee.std_logic_1164.all;
use IEEE.NUMERIC_STD.all;

library FACT_FAD_lib;
use FACT_FAD_lib.fad_definitions.all;


ENTITY phase_shifter IS

        PORT(
                CLK : IN std_logic;
                rst : out std_logic := '0'; --asynch in of DCM
                
                -- interface to: clock_generator_variable_PS_struct.vhd 
                PSCLK : OUT std_logic;
                PSEN : OUT std_logic := '0'; 
                PSINCDEC : OUT std_logic := '1'; -- default is 'incrementing'
                PSDONE : IN std_logic; -- will pulse once, if phase shifting was done.
                LOCKED : IN std_logic; -- when is this going high?
                
                
                -- interface to: w5300_modul.vhd
                shift_phase : IN std_logic;
                direction : IN std_logic; -- corresponds to 'PSINCDEC'
                reset_DCM : in std_logic; -- asynch in: orders us, to reset the DCM
                
                -- status:
                shifting : OUT std_logic := '0';
                ready : OUT std_logic := '0';
                
                locked_status_o : OUT std_logic;
                ready_status_o : OUT std_logic;
                offset : OUT std_logic_vector (7 DOWNTO 0) := (OTHERS => '0')
                
                
        );
END phase_shifter;

-- usage:
-- w5300_modul will set 'direction' to desired direction and pulse 'shift_phase' once
-- to initiate a phase shifting process.
-- while phase shifting, 'shifting' will show '1' and further pulses will be discarded.
-- 'offset' shows the number of phase_shift steps that have been performed. 
-- ready is high, when DCM is LOCKED and not phase_shifting.
-- DCM_status is a copy, of the STATUS input.
-- DCM_locked is a copy of LOCKED
-- 
-- how it works internally:
-- PSCLK is connected to clk, always.
--
-- main FSM goes from init to ready, when LOCKED is high.
-- main FSM goes from ready to shifting, when shift_phase goes high.
--              when in shifting: 
--                      PSINCDEC is set to 'direction'
--                      PSEN is set high
--                      shifting is set high
--                      next state waiting-for-done is entered
--
--              when in waiting-for-done:
--                      PSEN is set low
--                      if PSDONE is found to be high.
--                      shifting is set low and state ready is entered.
--
--      whenever LOCKED goes low FSM enters 'init' state
--              when in init state:
--                      'ready' is set low

architecture first_behave of phase_shifter is
        constant OFFS_MIN : integer := -51;
        constant OFFS_MAX : integer := 51;
                
        type states is (INIT, READY_STATE, PRE_SHIFTING_STATE, SHIFTING_STATE, WAITINGFORDONE, RESET_STATE); 
        signal state : states := INIT;
        
        signal local_direction : std_logic;
        signal offset_int : integer range OFFS_MIN to OFFS_MAX := 0;
        signal lower_limit_reached : std_logic := '0';
        signal upper_limit_reached : std_logic := '0';
                
        signal reset_dcm_sr : std_logic_vector(1 downto 0) := "00";
        signal shift_phase_sr : std_logic_vector(1 downto 0) := "00";
        signal ready_int : std_logic := '0';
begin

-- concurrent statements:
ready <= ready_int;
PSCLK <= CLK;
offset <= std_logic_vector(to_signed(offset_int,8));
locked_status_o <= LOCKED;
ready_status_o <= ready_int;

        -- MAIN FSM
        FSM: process(CLK)
        begin
        
        if rising_edge(CLK) then
        reset_dcm_sr <= reset_dcm_sr(1) & reset_DCM;  --synch in
        shift_phase_sr <= shift_phase_sr(1) & shift_phase; --synch in
        
                case state is
                -- INIT state: here the FSM is idling, when LOCKED is not HIGH.
                when INIT =>
                        rst <= '0';
                        ready_int <= '0';
                        shifting <= '0';
                        PSEN <= '0';
                        offset_int <= 0;
                        if (LOCKED = '1') then
                                state <= READY_STATE;
                        else 
                                state <= INIT;
                        end if;
                        
                -- RESET state: when ordered to do so: DCM is reseted and FSM send back to INIT. 
                when RESET_STATE =>
                        rst <= '1';
                        ready_int <= '0';
                        shifting <= '0';
                        PSEN <= '0';
                        state <= INIT;
                        
                -- READY_STATE state: here FSM is waiting for the 'shift_phase' to go high, or
                -- if reset_DCM goes high, we will reset the DCM and go back to init.
                when READY_STATE =>
                        ready_int <= '1';
                        shifting <= '0';
                        PSEN <= '0';

                        lower_limit_reached <='0';
                        upper_limit_reached <='0';
                        if (offset_int = OFFS_MIN) then 
                                lower_limit_reached <= '1';
                        elsif (offset_int = OFFS_MAX) then
                                upper_limit_reached <= '1';
                        end if;
                        
                        if (shift_phase_sr = "01") then
                                local_direction <= direction; -- direction is sampled, once 'shift_phase' goes high
                                state <= PRE_SHIFTING_STATE;
                        else
                                state <= READY_STATE;
                        end if;
                        
                        if (reset_dcm_sr = "01") then   
                                state <= RESET_STATE;
                        end if;
                
                -- checks if possible to shift in asked direction. If not ... back to READY.
                when PRE_SHIFTING_STATE =>
                ready_int <= '0';
                        if (local_direction = '1' and upper_limit_reached = '1') or
                                (local_direction = '0' and lower_limit_reached = '1') then
                                state <= READY_STATE;
                        else
                                state <= SHIFTING_STATE;
                        end if;
                
                
                -- SHIFTING_STATE state: PSENC is set HIGH here and set low in the next state.
                when SHIFTING_STATE =>
                        ready_int <= '0';
                        shifting <= '1';
                        PSEN <= '1';
                        PSINCDEC <= local_direction; -- this is the value of 'direction', when 'shift_phase' went up.
                        state <= WAITINGFORDONE;
                
                -- WAITINGFORDONE state: PSENC is set LOW, ensuring that is was high only one clock cycle.
                when WAITINGFORDONE =>
                        ready_int <= '0';
                        shifting <= '1';
                        PSEN <= '0';
                        if (PSDONE = '1') then
                                state <= READY_STATE;
                                if (local_direction = '1') then
                                        offset_int <= offset_int + 1;
                                else
                                        offset_int <= offset_int - 1;
                                end if;
                        else
                                state <= WAITINGFORDONE;
                        end if;
                        
                -- does this work????
                when others =>
                        state <= RESET_STATE;
                
                end case;
                end if;
        end process;

end first_behave;