hw/qcounter.vhd

   1 library ieee;
   2 use ieee.std_logic_1164.all;
   3 use ieee.std_logic_arith.all;
   4 use ieee.std_logic_unsigned.all;
   5 use ieee.numeric_std.all;
   6 use work.lx_rocon_pkg.all;
   7
   8 -- Quadcounter (for IRC)
   9
  10 entity qcounter is
  11   port
  12         (
  13                 -- Inputs
  14     clk_i              : in std_logic;
  15     reset_i            : in std_logic;
  16     a0_i, b0_i         : in std_logic;
  17                 index0_i           : in std_logic;
  18                 -- Outputs
  19     qcount_o           : out std_logic_vector (31 downto 0);
  20                 qcount_index_o     : out std_logic_vector (31 downto 0);
  21     a_rise_o, a_fall_o : out std_logic;
  22                 b_rise_o, b_fall_o : out std_logic;
  23                 ab_event_o         : out std_logic;
  24     ab_error_o         : out std_logic
  25   );
  26 end qcounter;
  27
  28 architecture behavioral of qcounter is
  29
  30         signal last_reset_s       : std_logic;
  31   signal a_s, b_s           : std_logic;
  32         signal a_prev_s, b_prev_s : std_logic;
  33         signal index_s            : std_logic;
  34   signal count_prev_s       : std_logic_vector (29 downto 0);
  35   signal count_s            : std_logic_vector (29 downto 0);
  36         signal count_index_prev_s : std_logic_vector (31 downto 0);
  37   signal count_index_s      : std_logic_vector (31 downto 0);
  38
  39 begin
  40         dff_a: dff2
  41         port map
  42         (
  43                 clk_i   => clk_i,
  44                 reset_i => '0',
  45                 d_i     => a0_i,
  46                 q_o     => a_s
  47         );
  48
  49   dff_b: dff2
  50         port map
  51         (
  52                 clk_i   => clk_i,
  53                 reset_i => '0',
  54                 d_i     => b0_i,
  55                 q_o     => b_s
  56         );
  57
  58         dff_index: dff2
  59         port map
  60         (
  61                 clk_i   => clk_i,
  62                 reset_i => '0',
  63                 d_i     => index0_i,
  64                 q_o     => index_s
  65         );
  66
  67         qcount_o(0)           <= a_s xor b_s;
  68         qcount_o(1)           <= b_s;
  69         qcount_o(31 downto 2) <= count_s;
  70
  71         qcount_index_o        <= count_index_s;
  72
  73 comb_event:
  74         process (reset_i, last_reset_s, a_prev_s, b_prev_s, a_s, b_s)
  75         begin
  76     a_rise_o   <= '0';
  77     a_fall_o   <= '0';
  78     b_rise_o   <= '0';
  79     b_fall_o   <= '0';
  80     ab_event_o <= '0';
  81     ab_error_o <= '0';
  82
  83                 if reset_i = '0' and last_reset_s = '0' then
  84                         if ((a_s xor a_prev_s) and (b_s xor b_prev_s)) = '1' then
  85                                 -- forbidden double transition
  86                                 ab_error_o <= '1';
  87                         else
  88                                 a_rise_o   <= (a_s xor a_prev_s) and a_s;
  89                                 a_fall_o   <= (a_s xor a_prev_s) and (not a_s);
  90                                 b_rise_o   <= (b_s xor b_prev_s) and b_s;
  91                                 b_fall_o   <= (b_s xor b_prev_s) and (not b_s);
  92                                 ab_event_o <= (a_s xor a_prev_s) or (b_s xor b_prev_s);
  93                         end if;
  94                 end if;
  95   end process;
  96
  97 comb_count:
  98         process (reset_i, last_reset_s, a_prev_s, b_prev_s, a_s, b_s,
  99                                                 index_s, count_prev_s, count_index_prev_s)
 100         begin
 101                 if reset_i = '1' or last_reset_s = '1' then
 102                         count_s                      <= count_prev_s;
 103                         count_index_s                <= count_index_prev_s;
 104                 elsif (a_prev_s = '0') and (b_prev_s = '1') and (a_s = '0') and
 105                                                 (b_s = '0') then
 106       count_s                      <= count_prev_s + 1;
 107                         if index_s = '1' then
 108                                 count_index_s(0)           <= a_s xor b_s;
 109                                 count_index_s(1)           <= b_s;
 110                                 count_index_s(31 downto 2) <= count_prev_s + 1;
 111                         else
 112                                 count_index_s              <= count_index_prev_s;
 113                         end if;
 114     elsif (a_prev_s = '0') and (b_prev_s = '0') and (a_s = '0') and
 115                                                 (b_s = '1') then
 116       count_s                      <= count_prev_s - 1;
 117
 118                         if index_s = '1' then
 119                                 count_index_s(0)           <= a_s xor b_s;
 120                                 count_index_s(1)           <= b_s;
 121                                 count_index_s(31 downto 2) <= count_prev_s - 1;
 122                         else
 123                                 count_index_s              <= count_index_prev_s;
 124                         end if;
 125     else
 126       count_s                      <= count_prev_s;
 127                         if index_s = '1' then
 128                                 count_index_s(0)           <= a_s xor b_s;
 129                                 count_index_s(1)           <= b_s;
 130                                 count_index_s(31 downto 2) <= count_prev_s;
 131                         else
 132                                 count_index_s              <= count_index_prev_s;
 133                         end if;
 134     end if;
 135
 136   end process;
 137
 138 seq:
 139         process (clk_i)
 140         begin
 141                 -- Reset for qcounter is synchronous and lasts at least one more cycle
 142                 -- to prevent hazardous states after releasing it
 143                 if clk_i = '1' and clk_i'event then
 144                         if reset_i = '0' then
 145                                 count_prev_s       <= count_s;
 146                                 count_index_prev_s <= count_index_s;
 147                         else
 148                                 count_prev_s       <= (others => '0');
 149                                 count_index_prev_s <= (others => '0');
 150                         end if;
 151                         a_prev_s             <= a_s;
 152                         b_prev_s             <= b_s;
 153                         last_reset_s         <= reset_i;
 154                 end if;
 155   end process;
 156
 157 end behavioral;