VHDL Papilio LED animation - pattern, speed, direction

papilioAnimatedLEDs.VHD

-- File: Blink.VHD -------

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity Blink is
 Port (
  PB : in  STD_LOGIC_VECTOR(7 downto 0);
  LED : inout  BIT_VECTOR(7 downto 0);
  clk : in STD_LOGIC
 );
end Blink;

architecture Behavioral of Blink is
	signal counter : STD_LOGIC_VECTOR(20 downto 0) := (others => '0');
	signal ticks : STD_LOGIC_VECTOR(1 downto 0) := (others => '0');
	signal dir : BIT := '0';
	signal fast : BIT := '0';
	constant speed: INTEGER := 19;
begin

	process(clk, PB)	
	begin
	
		if (clk'event and clk =  '1') then
			counter <= counter + 1;
		end if; 		
		
		if (rising_edge(counter(speed))) then
			if(fast = '1') then ticks <= ticks + 2;
			else ticks <= ticks + 1;
			end if;			
		end if;
		
		if    (PB(0) = '1') 	then LED <= "00000001"; 
		elsif (PB(2) = '1') 	then LED <= "00001111";
		elsif (PB(4) = '1') 	then LED <= "01111111"; 
		elsif (PB(6) = '1') 	then LED <= "11001100";
		elsif (PB(1) = '1') 	then dir <= '0';
		elsif (PB(7) = '1') 	then dir <= '1';
		elsif (PB(3) = '1') 	then fast <= '0';
		elsif (PB(5) = '1') 	then fast <= '1';
		elsif rising_edge(ticks(1)) then	
			if(dir = '0') then LED <= LED ror 1; 
			else LED <= LED rol 1; 
			end if;
		end if;
		
	end process;

end Behavioral;



##################
##   UCF file   ##
##################

NET "clk" LOC = "P89" | IOSTANDARD = LVCMOS25 | PERIOD = 31.25ns ;
# Wing2 Column C
NET "LED<7>" LOC = "P91" ;		
NET "LED<6>" LOC = "P94" ;  
NET "LED<5>" LOC = "P98" ; 	
NET "LED<4>" LOC = "P3" ;  		
NET "LED<3>" LOC = "P5" ;  	 
NET "LED<2>" LOC = "P10" ;	
NET "LED<1>" LOC = "P12" ;	
NET "LED<0>" LOC = "P16" ;	

NET "PB<7>" LOC = "P92" ;  	
NET "PB<6>" LOC = "P95" ;  	 	
NET "PB<5>" LOC = "P2" ;  
NET "PB<4>" LOC = "P4" ;  
NET "PB<3>" LOC = "P9" ;  
NET "PB<2>" LOC = "P11" ;	
NET "PB<1>" LOC = "P15" ;	
NET "PB<0>" LOC = "P17" ;