From e29d030c7ccc11c4c880908901d7a6c63a11ce34 Mon Sep 17 00:00:00 2001
From: Rutherther <rutherther@proton.me>
Date: Thu, 28 Dec 2023 15:38:09 +0100
Subject: [PATCH] feat: add utility entities

Delay, metastability filter, open drain buffer, synchronous edge detector
---
 src/utils/delay.vhd                | 36 ++++++++++++++++++++
 src/utils/metastability_filter.vhd | 26 ++++++++++++++
 src/utils/open_drain_buffer.vhd    | 25 ++++++++++++++
 src/utils/pulse_delay.vhd          |  0
 src/utils/sync_edge_detector.vhd   | 54 ++++++++++++++++++++++++++++++
 5 files changed, 141 insertions(+)
 create mode 100644 src/utils/delay.vhd
 create mode 100644 src/utils/metastability_filter.vhd
 create mode 100644 src/utils/open_drain_buffer.vhd
 create mode 100644 src/utils/pulse_delay.vhd
 create mode 100644 src/utils/sync_edge_detector.vhd

diff --git a/src/utils/delay.vhd b/src/utils/delay.vhd
new file mode 100644
index 0000000000000000000000000000000000000000..3b8380fcc04602eeb60ce63d9568218c9e5f51d2
--- /dev/null
+++ b/src/utils/delay.vhd
@@ -0,0 +1,36 @@
+library ieee;
+use ieee.std_logic_1164.all;
+
+entity delay is
+  generic (
+    DELAY : natural);
+
+  port (
+    clk_i   : in std_logic;
+    rst_in  : in std_logic;
+    signal_i : in std_logic;
+    signal_o : out std_logic);
+
+end entity delay;
+
+architecture a1 of delay is
+  signal DELAYED_PULSE_POS : natural := DELAY - 1;
+  signal curr_pulses : std_logic_vector(DELAYED_PULSE_POS downto 0);
+  signal next_pulses : std_logic_vector(DELAYED_PULSE_POS downto 0);
+begin  -- architecture a1
+
+  signal_o <= curr_pulses(DELAYED_PULSE_POS);
+  next_pulses <= curr_pulses(DELAYED_PULSE_POS - 1 downto 1) & signal_i;
+
+  set_regs: process (clk_i) is
+  begin  -- process set_regs
+    if rising_edge(clk_i) then          -- rising clock edge
+      if rst_in = '0' then              -- synchronous reset (active low)
+        curr_pulses <= (others => '0');
+      else
+        curr_pulses <= next_pulses;
+      end if;
+    end if;
+  end process set_regs;
+
+end architecture a1;
diff --git a/src/utils/metastability_filter.vhd b/src/utils/metastability_filter.vhd
new file mode 100644
index 0000000000000000000000000000000000000000..cb507717668907bf8e1fbaea0ac23fa8139a3480
--- /dev/null
+++ b/src/utils/metastability_filter.vhd
@@ -0,0 +1,26 @@
+library ieee;
+use ieee.std_logic_1164.all;
+
+entity metastability_filter is
+
+  port (
+    clk_i    : in  std_logic;
+    signal_i : in  std_logic;
+    signal_o : out std_logic);
+
+end entity metastability_filter;
+
+architecture a1 of metastability_filter is
+
+begin  -- architecture a1
+
+  entity work.delay
+    generic map (
+      DELAY => 2)
+    port map (
+      clk_i   => clk_i,
+      rst_in  => '1',
+      signal_i => signal_i,
+      signal_o => signal_o);
+
+end architecture a1;
diff --git a/src/utils/open_drain_buffer.vhd b/src/utils/open_drain_buffer.vhd
new file mode 100644
index 0000000000000000000000000000000000000000..dbfa2d62233262f3754be0a64a53fa160d38fcb6
--- /dev/null
+++ b/src/utils/open_drain_buffer.vhd
@@ -0,0 +1,25 @@
+library ieee;
+use ieee.std_logic_1164.all;
+
+entity open_drain_buffer is
+
+  port (
+    pad_io   : inout std_logic;         -- The pad itself, will be set to 'Z'
+                                        -- when enable_i = '0'
+    enable_i : in    std_logic;         -- Whether to enable output, ie. set
+                                        -- pad to '0' for enable_i = '1'
+    state_o  : out   std_logic);        -- The state of the pad, relevant if
+                                        -- enable_i = '0'
+
+end entity open_drain_buffer;
+
+architecture a1 of open_drain_buffer is
+
+begin  -- architecture a1
+
+  pad_io <= '0' when enable_i = '0' else
+            'Z';
+
+  state_o <= pad_io;
+
+end architecture a1;
diff --git a/src/utils/pulse_delay.vhd b/src/utils/pulse_delay.vhd
new file mode 100644
index 0000000000000000000000000000000000000000..e69de29bb2d1d6434b8b29ae775ad8c2e48c5391
diff --git a/src/utils/sync_edge_detector.vhd b/src/utils/sync_edge_detector.vhd
new file mode 100644
index 0000000000000000000000000000000000000000..0a75f774d1474c9733a864365c05c829404b9e48
--- /dev/null
+++ b/src/utils/sync_edge_detector.vhd
@@ -0,0 +1,54 @@
+-------------------------------------------------------------------------------
+-- Title      : Synchronous edge detector
+-- Project    :
+-------------------------------------------------------------------------------
+-- File       : sync_edge_detector.vhd
+-- Author     : Frantisek Bohacek  <rutherther@protonmail.com>
+-- Created    : 2023-11-26
+-- Last update: 2023-11-26
+-- Platform   :
+-- Standard   : VHDL'93/02
+-------------------------------------------------------------------------------
+-- Description: Detects edges in signal_i, synchronously to clk_i
+-------------------------------------------------------------------------------
+-- Copyright (c) 2023
+-------------------------------------------------------------------------------
+-- Revisions  :
+-- Date        Version  Author  Description
+-- 2023-11-26  1.0      ruther	Created
+-------------------------------------------------------------------------------
+
+
+library ieee;
+use ieee.std_logic_1164.all;
+
+entity sync_edge_detector is
+
+  port (
+    clk_i          : in  std_logic;
+    signal_i       : in  std_logic;
+    rising_edge_o  : out std_logic;
+    falling_edge_o : out std_logic);
+
+end entity sync_edge_detector;
+
+architecture a1 of sync_edge_detector is
+  signal reg_prev_signal : std_logic;
+  signal next_prev_signal : std_logic;
+begin  -- architecture a1
+  next_prev_signal <= signal_i;
+
+  rising_edge_o <= '1' when reg_prev_signal = '0' and signal_i = '1' else
+                   '0';
+
+  falling_edge_o <= '1' when reg_prev_signal = '1' and signal_i = '0' else
+                    '0';
+
+  set_next: process (clk_i) is
+  begin  -- process set_next
+    if rising_edge(clk_i) then          -- rising clock edge
+      reg_prev_signal <= next_prev_signal;
+    end if;
+  end process set_next;
+
+end architecture a1;