From 33d341bbbb8d41ccfbe5e4d826de332798d4cd9d Mon Sep 17 00:00:00 2001
From: Rutherther <rutherther@proton.me>
Date: Fri, 29 Dec 2023 20:53:47 +0100
Subject: [PATCH] feat: add stateful sda, scl switch

---
 src/i2c/sdascl_enabler.vhd | 91 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)
 create mode 100644 src/i2c/sdascl_enabler.vhd

diff --git a/src/i2c/sdascl_enabler.vhd b/src/i2c/sdascl_enabler.vhd
new file mode 100644
index 0000000..14f1a54
--- /dev/null
+++ b/src/i2c/sdascl_enabler.vhd
@@ -0,0 +1,91 @@
+library ieee;
+use ieee.std_logic_1164.all;
+
+library utils;
+
+entity sdascl_enabler is
+  generic (
+    DELAY : natural);
+
+  port (
+    clk_i          : in  std_logic;
+    rst_in         : in  std_logic;
+
+    scl_i : in std_logic;
+    sda_i : in std_logic;
+
+    scl_falling_pulse_i : in std_logic;
+
+    transmitting_i : in  std_logic;
+    receiving_i    : in  std_logic;
+
+    expects_ack_i  : in  std_logic;
+    generate_ack_i : in  std_logic;
+
+    tx_sda_i         : in std_logic;
+    tx_scl_stretch_i : in std_logic;
+    rx_scl_stretch_i : in std_logic;
+
+    sda_enable_o   : out std_logic;
+    scl_enable_o   : out std_logic);
+
+end entity sdascl_enabler;
+
+architecture a1 of sdascl_enabler is
+  type state_t is (TRANSMITTING, RECEIVING, EXPECTS_ACK, GENERATE_ACK, NONE);
+  signal curr_state : state_t;
+  signal next_state : state_t;
+
+  signal curr_scl_enable : std_logic := '0';
+  signal next_scl_enable : std_logic;
+
+  signal any_stretch : std_logic;
+  signal should_start_stretch : std_logic;
+
+  signal delayed_scl_pulse : std_logic;
+begin  -- architecture a1
+  scl_falling_delay: entity utils.delay
+    generic map (
+      DELAY => DELAY)
+    port map (
+      clk_i   => clk_i,
+      rst_in  => rst_in,
+      signal_i => scl_falling_pulse_i,
+      signal_o => delayed_scl_pulse);
+
+  scl_enable_o <= curr_scl_enable;
+  sda_enable_o <= '0' when curr_state = EXPECTS_ACK else
+                  '1' when curr_state = GENERATE_ACK else
+                  not tx_sda_i when curr_state = TRANSMITTING else
+                  '0';
+
+  any_stretch <= '1' when
+                    (tx_scl_stretch_i = '1' and transmitting_i = '1') or
+                    (rx_scl_stretch_i = '1' and receiving_i = '1')
+                 else '0';
+  should_start_stretch <= '1' when any_stretch = '1' and scl_i = '0' else '0';
+
+  next_scl_enable <= '1' when should_start_stretch = '1' else
+                     '0' when any_stretch = '0' else
+                     curr_scl_enable;
+
+  next_state <= TRANSMITTING when transmitting_i = '1' and delayed_scl_pulse = '1' else
+                RECEIVING when receiving_i = '1' and delayed_scl_pulse = '1'else
+                EXPECTS_ACK when expects_ack_i = '1' and delayed_scl_pulse = '1'else
+                GENERATE_ACK when generate_ack_i = '1' and delayed_scl_pulse = '1'else
+                curr_state;
+
+  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_state <= NONE;
+        curr_scl_enable <= '0';
+      else
+        curr_state <= next_state;
+        curr_scl_enable <= next_scl_enable;
+      end if;
+    end if;
+  end process set_regs;
+
+end architecture a1;
-- 
2.48.1