wic_main: simplify periodic VAR3 updating

There is no need for updating it periodically with a counter. It's enough to update it after previous VAR3 was produced (even if there was no change in inputs).

wic_main: simplify periodic VAR3 updating
There is no need for updating it periodically with a counter. It's enough to update it after previous VAR3 was produced (even if there was no change in inputs).
252483b4 · Grzegorz Daniluk · c7dfc62b · 252483b4
Commit 252483b4 authored Aug 17, 2018 by Grzegorz Daniluk
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Showing with 7 additions and 9 deletions

wic_main.vhd hdl/rtl/wic_modules/wic_main.vhd +7 -9

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--- a/hdl/rtl/wic_modules/wic_main.vhd
+++ b/hdl/rtl/wic_modules/wic_main.vhd
@@ -91,7 +91,6 @@ architecture rtl of wic_main is
  constant c_NF_VAR_MAXSIZE       : unsigned(9 downto 0) := to_unsigned(124, 10);
  --------------------------

-  constant c_UPDATE_PERIOD : unsigned(15 downto 0) := x"FFFF";
  type t_state is (IDLE, READ_LEN, READ_VAR1, WRITE_VAR3);

  signal state   : t_state;
@@ -106,7 +105,7 @@ architecture rtl of wic_main is
  signal var1_read    : std_logic;

  -- VAR3 producing
-  signal refresh_cnt   : unsigned(15 downto 0);
+  signal var3_rdy_d0   : std_logic;
  signal var3_reg      : t_wic_var;
  signal var3_refresh  : std_logic; -- triggers sending status of all inputs
  signal var3_written  : std_logic;
@@ -316,23 +315,22 @@ begin
  loops_changed <= '1' when(f_detect_change(slots_in_synced, slots_in_reg, g_NUM)) else
                   '0';

-  -- Counter for periodic VAR3 updates
+  -- process monitors when a refresh of VAR3 should be triggered
  process(clk_i)
  begin
    if rising_edge(clk_i) then
      if rst_n_i = '0' then
        var3_refresh   <= '0';
-        refresh_cnt    <= (others=>'0');
        in_error       <= '0'; -- TODO: add loops toggling detection
+        var3_rdy_d0    <= '0';
      else
-        if refresh_cnt = c_UPDATE_PERIOD or loops_changed = '1' then
+        var3_rdy_d0    <= var3_rdy_i;
+        if (var3_rdy_d0 = '0' and var3_rdy_i = '1') or loops_changed = '1' then
+          -- force the state machine to write VAR3 if inputs have changed, or
+          -- at least after previous VAR3 was read - to show that we're alive.
          var3_refresh <= '1';
-          refresh_cnt  <= (others=>'0');
        elsif var3_written = '1' then
          var3_refresh <= '0';
-          refresh_cnt  <= refresh_cnt + 1;
-        else
-          refresh_cnt  <= refresh_cnt + 1;
        end if;
      end if;
    end if;