Need to time outputs

R

RRamsey118

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Hey I'm supposed to be making a digital pattern generator for class, but I can't figure out how to slow down the outputs. When I use the logic analyzer it only goes gets the last output. I tried using wait statements but I can only have one per process. My book is pretty crappy and I can't seem to really find anything on the internet, can someone help me out?

Edit: forgot to mention some of the inptus, scancode_in is a command from a ps2 keyboard, with F0 saying released key and 5A signifying return. Choice is controlled by scan code in a different part of the system. Clock_48MHZ is a 48mhz clock on the board we're using. Custom input is just a custom input std_logic vector, don't really care about timing on that one.

My code
Code: 
LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_ARITH.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;

ENTITY PRESETS IS
	PORT(	current_choice    	:IN		STD_LOGIC_VECTOR(3 DOWNTO 0);
			custom_input		:IN		STD_LOGIC_VECTOR(17 DOWNTO 0);
			preset_output		:OUT	STD_LOGIC_VECTOR(17 DOWNTO 0);
			scancode_in			:IN		STD_LOGIC_VECTOR(7 DOWNTO 0);
			clk_48mhz			:IN		STD_LOGIC);
END PRESETS;
	
ARCHITECTURE a OF PRESETS IS
	SIGNAL SCANLAST					:STD_LOGIC_VECTOR(7 DOWNTO 0);
	SIGNAL preset_last				:STD_LOGIC_VECTOR(17 DOWNTO 0);

BEGIN
	PROCESS(scancode_in, current_choice, clk_48mhz)
		BEGIN
			IF ((scancode_in = x"5A") AND (SCANLAST = x"F0")) THEN
				CASE current_choice(3 DOWNTO 0) IS
					WHEN "0000" =>  -- Count up
						preset_last(17 downto 0) <= "000000000000000000";
						preset_output <= preset_last;
						
						
					WHEN "0001" => -- count down
						preset_last(17 downto 0) <= "111111111111111111";
						preset_output <= preset_last;
						

						
					WHEN "0010" => --BIT SHIFT L to R
						
						preset_last(17 downto 0) <= "000000000000000000";
						preset_output <= preset_last;
						
						preset_last(17 downto 0) <= "100000000000000000";
						preset_output <= preset_last;					
								
						for i in 0 to 16 loop
						preset_output(17-i downto 16-i) <= "01";
						end loop;
						
					WHEN "0011" =>  -- bit shift R to L
						
						preset_output(17 downto 0) <= "000000000000000000";
						preset_output(17 downto 0) <= "000000000000000001";				
						preset_output(17 downto 0) <= "000000000000000010";				
						preset_output(17 downto 0) <= "000000000000000100";						
						preset_output(17 downto 0) <= "000000000000001000";						
						preset_output(17 downto 0) <= "000000000000010000";
						preset_output(17 downto 0) <= "000000000000100000";
						preset_output(17 downto 0) <= "000000000001000000";
						preset_output(17 downto 0) <= "000000000010000000";
						preset_output(17 downto 0) <= "000000000100000000";
						preset_output(17 downto 0) <= "000000001000000000";
						preset_output(17 downto 0) <= "000000010000000000";
						preset_output(17 downto 0) <= "000000100000000000";
						preset_output(17 downto 0) <= "000001000000000000";
						preset_output(17 downto 0) <= "000010000000000000";
						preset_output(17 downto 0) <= "000100000000000000";
						preset_output(17 downto 0) <= "001000000000000000";
						preset_output(17 downto 0) <= "010000000000000000";
						preset_output(17 downto 0) <= "100000000000000000";
					
					WHEN "0100" => -- all bits on from L to R 				
						
						preset_output <= "000000000000000000";
						preset_output <= "100000000000000000";
						preset_output <= "110000000000000000";
						preset_output <= "111000000000000000";
						preset_output <= "111100000000000000";
						preset_output <= "111110000000000000";
						preset_output <= "111111000000000000";
						preset_output <= "111111100000000000";
						preset_output <= "111111110000000000";
						preset_output <= "111111111000000000";
						preset_output <= "111111111100000000";
						preset_output <= "111111111110000000";
						preset_output <= "111111111111000000";
						preset_output <= "111111111111100000";
						preset_output <= "111111111111110000";
						preset_output <= "111111111111111000";
						preset_output <= "111111111111111100";
						preset_output <= "111111111111111110";
						preset_output <= "111111111111111111";
					
					
					WHEN "0110" => --OR all bits off from L to R
						preset_output <= NOT "000000000000000000";
						preset_output <= NOT "110000000000000000";
						preset_output <= NOT "111000000000000000";
						preset_output <= NOT "111100000000000000";
						preset_output <= NOT "111110000000000000";
						preset_output <= NOT "111111000000000000";
						preset_output <= NOT "111111100000000000";
						preset_output <= NOT "111111110000000000";
						preset_output <= NOT "111111111000000000";
						preset_output <= NOT "111111111100000000";
						preset_output <= NOT "111111111110000000";
						preset_output <= NOT "111111111111000000";
						preset_output <= NOT "111111111111100000";
						preset_output <= NOT "111111111111110000";
						preset_output <= NOT "111111111111111000";
						preset_output <= NOT "111111111111111100";
						preset_output <= NOT "111111111111111110";
						preset_output <= NOT "111111111111111111";

					WHEN "0101" => -- all bits on from R to L
						preset_output <= "000000000000000001";
						preset_output <= "000000000000000011";
						preset_output <= "000000000000000111";
						preset_output <= "000000000000001111";
						preset_output <= "000000000000011111";
						preset_output <= "000000000000111111";
						preset_output <= "000000000001111111";
						preset_output <= "000000000011111111";
						preset_output <= "000000000111111111";
						preset_output <= "000000001111111111";
						preset_output <= "000000011111111111";
						preset_output <= "000000111111111111";
						preset_output <= "000001111111111111";
						preset_output <= "000011111111111111";
						preset_output <= "000111111111111111";
						preset_output <= "001111111111111111";
						preset_output <= "011111111111111111";
						preset_output <= "111111111111111111";
					
					
					WHEN "0111" => -- all bits off from R to L
						preset_output <= NOT "000000000000000001";
						preset_output <= NOT "000000000000000011";
						preset_output <= NOT "000000000000000111";
						preset_output <= NOT "000000000000001111";
						preset_output <= NOT "000000000000011111";
						preset_output <= NOT "000000000000111111";
						preset_output <= NOT "000000000001111111";
						preset_output <= NOT "000000000011111111";
						preset_output <= NOT "000000000111111111";
						preset_output <= NOT "000000001111111111";
						preset_output <= NOT "000000011111111111";
						preset_output <= NOT "000000111111111111";
						preset_output <= NOT "000001111111111111";
						preset_output <= NOT "000011111111111111";
						preset_output <= NOT "000111111111111111";
						preset_output <= NOT "001111111111111111";
						preset_output <= NOT "011111111111111111";
						preset_output <= NOT "111111111111111111";
					
					WHEN ("1000" OR "1001")=> -- Zeros with collapsing ones
						preset_last <= "000000000000000000";
						IF current_choice="1001" THEN
						preset_output <= preset_last(17 downto 0); --for collapsing ones
						ELSE
						preset_output <= NOT preset_last;		-- for collapsing zeros
						end if;
						preset_last <= "100000000000000001";
						IF current_choice="1001" THEN
						preset_output <= preset_last(17 downto 0); --for collapsing ones
						ELSE
						preset_output <= NOT preset_last;		-- for collapsing zeros
						end if;
						preset_last <= "110000000000000011";
						IF current_choice="1001" THEN
						preset_output <= preset_last(17 downto 0); --for collapsing ones
						ELSE
						preset_output <= NOT preset_last;		-- for collapsing zeros
						end if;
						preset_last <= "111000000000000111";
						IF current_choice="1001" THEN
						preset_output <= preset_last(17 downto 0); --for collapsing ones
						ELSE
						preset_output <= NOT preset_last;		-- for collapsing zeros
						end if;
						preset_last <= "111100000000001111";
						IF current_choice="1001" THEN
						preset_output <= preset_last(17 downto 0); --for collapsing ones
						ELSE
						preset_output <= NOT preset_last;		-- for collapsing zeros
						end if;
						preset_last <= "111110000000011111";
						IF current_choice="1001" THEN
						preset_output <= preset_last(17 downto 0); --for collapsing ones
						ELSE
						preset_output <= NOT preset_last;		-- for collapsing zeros
						end if;
						preset_last <= "111111000000111111";
						IF current_choice="1001" THEN
						preset_output <= preset_last(17 downto 0); --for collapsing ones
						ELSE
						preset_output <= NOT preset_last;		-- for collapsing zeros
						end if;
						preset_last <= "111111100001111111";
						IF current_choice="1001" THEN
						preset_output <= preset_last(17 downto 0); --for collapsing ones
						ELSE
						preset_output <= NOT preset_last;		-- for collapsing zeros
						end if;
						preset_last <= "111111110011111111";
						IF current_choice="1001" THEN
						preset_output <= preset_last(17 downto 0); --for collapsing ones
						ELSE
						preset_output <= NOT preset_last;		-- for collapsing zeros
						end if;
						preset_last <= "111111111111111111";
						IF current_choice="1001" THEN
						preset_output <= preset_last(17 downto 0); --for collapsing ones
						ELSE
						preset_output <= NOT preset_last;		-- for collapsing zeros
						end if;
					
					WHEN OTHERS =>
						-- do nothing
					
				end case;
			
			end if;
			
			IF current_choice = "1010" THEN
				preset_output(17 downto 0) <= custom_input(17 downto 0);
			END IF;	
				
			SCANLAST <= SCANCODE_IN;
	
END PROCESS;



END a;
 
Last edited:
J

jeppe

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Well you must realize - when a signal assigned inside a process will it always be the last assignment that "wins". All the previous "forgotten".

Please search for the intactive book at VHDL - Evita to learn more - speciallly chapter 6.

My surgestion will be:

1) Put wait for xx ns (but Im not sure this will work together with the sensitivitylist)
2) put after xx ns statements like xx<"00" after 1 ns (same problem as above)
3) make a more complex statemachine driven by the 48 MHz clock (complicated :-(

Hope this made sense
Jeppe
 
R

RRamsey118

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I tried using "wait for XX ns;" and the thing yelled at me saying I needed "until" which seems wrong to me. Either way I don't think it'll let me have multiple wait statements will it?

Either way, I guess I'll start working on a different design then. Thanks.
(unless someone has a magic fix, which would be awesome)
 
J

jeppe

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Well indeed: The only way your allowed to generate this kind waveform will be some kind of state machine, counter or shiftregister which controlled by the 48MHz clock.
I forgot to mention - The wait for statement not for synthesizing.
Jeppe
 

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