dmtd_with_deglitcher: added clock enable input to allow for undersampling/gating

191c3bd6 · Tomasz Wlostowski · 814e2ab2 · 191c3bd6
Commit 191c3bd6 authored Mar 08, 2012 by Tomasz Wlostowski
Show whitespace changes
Inline Side-by-side

Showing with 44 additions and 37 deletions

dmtd_with_deglitcher.vhd modules/timing/dmtd_with_deglitcher.vhd +44 -37

No files found.
--- a/modules/timing/dmtd_with_deglitcher.vhd
+++ b/modules/timing/dmtd_with_deglitcher.vhd
@@ -6,7 +6,7 @@
 -- Author     : Tomasz Wlostowski
 -- Company    : CERN BE-Co-HT
 -- Created    : 2010-02-25
-- Last update: 2011-10-29
+-- Last update: 2012-03-06
 -- Platform   : FPGA-generic
 -- Standard   : VHDL '93
 -------------------------------------------------------------------------------
@@ -56,7 +56,7 @@ entity dmtd_with_deglitcher is
    -- the following formula:
    -- g_counter_bits = log2(f_in / abs(f_in - f_dmtd)) + 1
    g_counter_bits : natural := 17;
-    g_chipscope: boolean := false
+    g_chipscope    : boolean := false
    );
  port (
    -- resets for different clock domains
@@ -80,6 +80,13 @@ entity dmtd_with_deglitcher is
    -- [clk_dmtd_i] phase shift direction: 1 - forward, 0 - backward
    shift_dir_i : in std_logic;

+    -- DMTD clock enable, active high. Can be used to reduce the DMTD sampling
+    -- frequency - for example, two 10 MHz signals cannot be sampled directly
+    -- with a 125 MHz clock, but it's possible with a 5 MHz reference, obtained
+    -- by asserting clk_dmtd_en_i every 25 clk_dmtd_i cycles.
+
+    clk_dmtd_en_i : in std_logic := '1';
+
    -- [clk_dmtd_i] deglitcher threshold
    deglitch_threshold_i : in std_logic_vector(15 downto 0);

@@ -167,7 +174,7 @@ begin  -- rtl
        state         <= WAIT_STABLE_0;
        free_cntr     <= (others => '0');
        new_edge_sreg <= (others => '0');
-      else
+      elsif(clk_dmtd_en_i = '1') then
        
        if (shift_en_i = '0') then      -- phase shifter
          free_cntr <= free_cntr + 1;
@@ -232,7 +239,7 @@ begin  -- rtl

  tag_stb_p1_o <= new_edge_p;

-  gc_extend_pulse_1: gc_extend_pulse
+  gc_extend_pulse_1 : gc_extend_pulse
    generic map (
      g_width => 3000)
    port map (
@@ -241,7 +248,7 @@ begin  -- rtl
      pulse_i    => new_edge_p,
      extended_o => dbg_dmtdout_o);

-gen_with_csc:  if(g_chipscope) generate
+  gen_with_csc : if(g_chipscope) generate

    chipscope_ila_1 : chipscope_ila
      port map (
@@ -258,13 +265,13 @@ gen_with_csc:  if(g_chipscope) generate

    
    TRIG0(tag_int'left downto 0)   <= std_logic_vector(tag_int);
-  TRIG0(31) <=clk_i_d3;
+    TRIG0(31)                      <= clk_i_d3;
    TRIG0(30)                      <= '1' when (state = WAIT_STABLE_0) else '0';
    TRIG0(29)                      <= '1' when (state = WAIT_EDGE)     else '0';
    TRIG0(28)                      <= '1' when (state = GOT_EDGE)      else '0';
    TRIG1(stab_cntr'left downto 0) <= std_logic_vector(stab_cntr);
    TRIG2(free_cntr'left downto 0) <= std_logic_vector(free_cntr);

-end generate gen_with_csc;
+  end generate gen_with_csc;
  
 end rtl;