common: added module that can count inc/dec pulses in different clk domains

This is needed for fixed-latency streamers. Module was written by Tom,
he added it to wr-cores whereas it belongs here, I've moved it.

modules/common/Manifest.py

@@ -33,4 +33,5 @@ files = [
     "gc_ds182x_interface.vhd",
     "gc_ds182x_readout.vhd",
     "gc_sfp_i2c_adapter.vhd",
+    "gc_async_counter_diff.vhd",
 ];

modules/common/gc_async_counter_diff.vhd

+--------------------------------------------------------------------------------
+-- CERN
+-- general-cores
+-- https://www.ohwr.org/project/general-cores
+--------------------------------------------------------------------------------
+--
+-- unit name  : gc_async_counter_diff.vhd
+-- author     : Tomasz Wlostowski
+-- description:
+-- 
+-- The module counts pulses on inc_i and dec_i inputs. Each input can be
+-- in its own clock domain. The module outputs difference in the number of
+-- pulses counted on inc_i and dec_i. The output is in the clock domain
+-- selected with the g_output_clock generic (that of inc_i or of dec_i).
+-- 
+-- Internally, Grey Codes are used and count encoded with Grey Code is
+-- resynchronized to the output clock domain. Therefore, the output
+-- is provided few clock cycles after pulse actually occured.
+--
+--------------------------------------------------------------------------------
+-- Copyright (c) 2019 CERN BE/CO/HT
+--------------------------------------------------------------------------------
+-- GNU LESSER GENERAL PUBLIC LICENSE
+--------------------------------------------------------------------------------
+-- This source file is free software; you can redistribute it
+-- and/or modify it under the terms of the GNU Lesser General
+-- Public License as published by the Free Software Foundation;
+-- either version 2.1 of the License, or (at your option) any
+-- later version.
+--
+-- This source is distributed in the hope that it will be
+-- useful, but WITHOUT ANY WARRANTY; without even the implied
+-- warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+-- PURPOSE.  See the GNU Lesser General Public License for more
+-- details
+--
+-- You should have received a copy of the GNU Lesser General
+-- Public License along with this source; if not, download it
+-- from http://www.gnu.org/licenses/lgpl-2.1.html
+--
+-------------------------------------------------------------------------------
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+
+use work.gencores_pkg.all;
+
+entity gc_async_counter_diff is
+  generic (
+    g_bits         : integer := 8;
+    g_output_clock : string  := "inc"
+    );
+  port
+    (
+      -- reset (g_output_clock clock domain)
+      rst_n_i : in std_logic;
+
+      -- increment clock
+      clk_inc_i : in std_logic;
+      -- decrement clock
+      clk_dec_i : in std_logic;
+
+      -- increment enable (clk_inc_i clock domain)
+      inc_i : in std_logic;
+
+      -- decrement enable (clk_inc_i clock domain)
+      dec_i : in std_logic;
+
+      -- current counter value, signed (g_output_clock clock domain)
+      counter_o : out std_logic_vector(g_bits downto 0)
+
+      );
+end gc_async_counter_diff;
+
+architecture rtl of gc_async_counter_diff is
+
+  signal cnt1_bin, cnt2_bin   : unsigned(g_bits downto 0);
+  signal cnt1_gray, cnt2_gray : std_logic_vector(g_bits downto 0);
+
+  signal cnt1_gray_out : std_logic_vector(g_bits downto 0);
+  signal cnt2_gray_out : std_logic_vector(g_bits downto 0);
+
+  signal rst_n_inc, rst_n_dec : std_logic;
+
+begin
+
+  U_SyncReset_to_IncClk : gc_sync_ffs
+    port map (
+      clk_i    => clk_inc_i,
+      rst_n_i  => '1',
+      data_i   => rst_n_i,
+      synced_o => rst_n_inc);
+
+  U_SyncReset_to_DecClk : gc_sync_ffs
+    port map (
+      clk_i    => clk_dec_i,
+      rst_n_i  => '1',
+      data_i   => rst_n_i,
+      synced_o => rst_n_dec);
+
+
+  p_count_up : process(clk_inc_i)
+  begin
+    if rising_edge(clk_inc_i) then
+      if rst_n_inc = '0' then
+        cnt1_bin  <= (others => '0');
+        cnt1_gray <= (others => '0');
+      else
+        if inc_i = '1' then
+          cnt1_bin <= cnt1_bin + 1;
+        end if;
+
+        cnt1_gray <= f_gray_encode(std_logic_vector(cnt1_bin));
+      end if;
+    end if;
+  end process;
+
+  p_count_down : process(clk_dec_i)
+  begin
+    if rising_edge(clk_dec_i) then
+      if rst_n_dec = '0' then
+        cnt2_bin  <= (others => '0');
+        cnt2_gray <= (others => '0');
+      else
+        if dec_i = '1' then
+          cnt2_bin <= cnt2_bin + 1;
+        end if;
+
+        cnt2_gray <= f_gray_encode(std_logic_vector(cnt2_bin));
+      end if;
+    end if;
+  end process;
+
+  gen_out_clock_is_inc : if g_output_clock = "inc" generate
+
+    cnt1_gray_out <= cnt1_gray;
+
+    U_Sync : gc_sync_register
+      generic map (
+        g_width => g_bits+1)
+      port map (
+        clk_i     => clk_inc_i,
+        rst_n_a_i => rst_n_i,
+        d_i       => cnt2_gray,
+        q_o       => cnt2_gray_out);
+
+  end generate gen_out_clock_is_inc;
+
+  gen_out_clock_is_dec : if g_output_clock = "dec" generate
+    cnt2_gray_out <= cnt2_gray;
+
+    U_Sync : gc_sync_register
+      generic map (
+        g_width => g_bits+1)
+      port map (
+        clk_i     => clk_dec_i,
+        rst_n_a_i => rst_n_i,
+        d_i       => cnt1_gray,
+        q_o       => cnt1_gray_out);
+  end generate gen_out_clock_is_dec;
+
+  counter_o <= std_logic_vector(unsigned(cnt2_gray_out) - unsigned(cnt1_gray_out));
+
+
+end rtl;

modules/common/gencores_pkg.vhd

@@ -623,6 +623,22 @@ package gencores_pkg is
       sfp_data_i      : in  std_logic_vector (127 downto 0));
   end component gc_sfp_i2c_adapter;
 
+  ------------------------------------------------------------------------------
+  -- Asynchronous counter inc/dec pulses
+  ------------------------------------------------------------------------------
+  component gc_async_counter_diff is
+    generic (
+      g_bits         : integer := 8;
+      g_output_clock : string  := "inc");
+    port (
+      rst_n_i : in std_logic;
+      clk_inc_i : in std_logic;
+      clk_dec_i : in std_logic;
+      inc_i : in std_logic;
+      dec_i : in std_logic;
+      counter_o : out std_logic_vector(g_bits downto 0));
+  end component gc_async_counter_diff;
+
   --============================================================================
   -- Procedures and functions
   --============================================================================