-- Tyler Lutz; July 26, 2011; 
-- Constant Fraction Timing Discriminator;
--Input->digital signal from ASIC, time from onboard clock;
--Output->calculated time of arrival of pulse based on intersection of an attenuated version of the pulse (to 30%) and a delayed version of the same pulse;

-------------------------------------------------------------------------
--((o))--((o))--((o))--((o))--((o))--((o))--((o))--((o))--((o))--((o))--
-------------------------------------------------------------------------

library ieee;
use ieee.std_logic_1164.all;

entity fitting_etc_CFD is
port(	pulse: in std_logic_vector (0 to 11);						--assumed that ASIC readout is in parallel(?), and if not it is easy to parallelize serial input
		clk: in std_logic;
	 OCFD: out std_logic_vector (0 to 11);         --Output for constant fraction discrimination timing calculation
	 OTEST: out std_logic_vector (0 to 11);       --for simulating miscellaneous calculations
end fitting_etc_CFD;  

-- ==I==I==I==I==I==I==I==I==I==I==I== --

architecture Herjolfssen7 of fitting_etc_CFD is					

	begin
  
    process(clk)
	variable accsec: integer :=0;										--"seconds" or any other arbitrary time unit, to be adjusted based on the frequency of clock used.
		type gaul is array(natural range <>) of integer;		--define unconstrained array type
	variable pulsebit: gaul (0 to 11);									--pulse is converted later to an integer for calculation purposes; this is an intermediate step
	variable multithreshold: gaul (0 to 2);							--stores our three constant threshold values for the multithresh mode
		variable pulsar: integer:=0;									-- intergized value of incoming pulse
		constant savescope: integer:=100;							--scope size of CFD delay memory and base line averager (here, last 1000 data points)
   	variable pulsarsave: gaul (0 to savescope+4);							--allows us to delay the pulse (the 10^10 is totally arbitrary)
variable letop: integer:=0;
		constant delay: integer:=4;              --delay length for CFD (150-200 ps = 4 using our clock specs (see testbench))
		variable eventprint: gaul (0 to 4);							--array output, listing arrival time against event number
      variable eventprintread: gaul (0 to 3);   --"scratchpaper" variable
	  variable inhibit_cfd: integer:=0;         --ditto


    
-- ==I==I==I==I==I==I==I==I==I==I==I== --

	begin

	if clk'event and clk='1' then      --program loops at clock rising edge 
	
letop:=(letop+1)mod 50;--1000000;  --slow down clock to 10MHz
	

if letop=0 then

accsec:=(accsec+1) mod 2**12;      --our stopwatch
	
                            --our oscilloscope data is converted to decimal stored in 'pulsar':
		for j in 0 to 11 loop				-- intigerizing the input pulse; logic vector to binary array to integer(pulsar)
				if pulse(j)='0' then
			pulsebit(j):=1;                --binary array
				elsif pulse(j)='1' then
			pulsebit(j):=0;
				end if;	
				if j=0 then	
				  pulsar:=pulsebit(0);      --a clever way to reinitialize the summand 'pulsar'
				else
				  pulsar:= pulsar+(pulsebit(j))*(2**(j));  --actual binary to integer conversion
				end if;
		end loop;

		
		  multithreshold(0):=11;           --specify desired threshold values for multithreshold claculations
			multithreshold(1):=14;
			multithreshold(2):=17;
			
		
if (pulsar<multithreshold(0) and pulsarsave(0)/=pulsar)then     --shut up output (supposing there is some) if pulse changes
          	for s in 0 to 11 loop
		         OCFD(s)<='0';              --reset to allow continued data acquisition
		       end loop;   
					inhibit_cfd:=0;
					eventprint(3):=0;
	       end if;
	       
	    
	 
		
				for k in savescope+2 downto 1 loop      	--pulse saver, for use in averaging and delaying pulse

					pulsarsave(k):=pulsarsave(k-1);            --shift data over one bin in pulsarsave
				end loop;
 
				 pulsarsave(0):=pulsar;								              --stick new incoming data in bin 0
				 
---- 

--  _/__/___/____/_____/______/_______/________/_________/__________/___________/____________/_____________/______________/_______________/ 
	
		if pulsar<multithreshold(0) then
			inhibit_cfd:=0;
		end if;
		
		if (pulsar>multithreshold(0)) and inhibit_cfd=0 then											--first threshold "arms" the Constant Fraction Discrimination calculation
		                                                     -- multiply by ten to reduce truncation error
			if (((-30*pulsar/10+10*pulsarsave(delay)) > 0)) then --and ((-30*pulsarsave(1)/10+10*pulsarsave((delay+1))) < 0)) then						--pulse attenuated to 30% (=3/10), inverted, and added to the delayed pulse  ('delay' indicates length of delay, to be adjusted based on actual clock freq) 
			eventprint(3):=accsec-delay;											              	--time of zerocrossing recorded (delay time subtracted)
			inhibit_cfd:=1;
			     		  		
	     	end loop;
			end if;
		end if;
		
		

--  _/__/___/____/_____/______/_______/________/_________/__________/___________/____________/_____________/______________/_______________/ 



tester:=eventprint(3);


	for v in 11 downto 0 loop                              --readout in parallel
		      		if tester>=(2**v) then
		         			OCFD(v)<='1'; 
		        				tester:=tester -2**v;			
		      		else
		      	  	  OCFD(v)<='0';
	     		  	end if;	
	     		  		
	     	end loop;
			
	 end if;	
end if;	 
  end process;
end Herjolfssen7;