From 3d4ae63afb93686dde6c3076db5c499ca4b68fa8 Mon Sep 17 00:00:00 2001
From: Derek Christ <dchrist@rhrk.uni-kl.de>
Date: Mon, 14 Nov 2022 16:41:54 +0100
Subject: [PATCH] Add scrolling timer

---
 soc/peripheral/scrolling_timer.vhd   | 50 ++++++++++++++++++
 soc/testbench/scrolling_timer_tb.vhd | 77 ++++++++++++++++++++++++++++
 2 files changed, 127 insertions(+)
 create mode 100644 soc/peripheral/scrolling_timer.vhd
 create mode 100644 soc/testbench/scrolling_timer_tb.vhd

diff --git a/soc/peripheral/scrolling_timer.vhd b/soc/peripheral/scrolling_timer.vhd
new file mode 100644
index 0000000..7f2d2ec
--- /dev/null
+++ b/soc/peripheral/scrolling_timer.vhd
@@ -0,0 +1,50 @@
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+
+entity scrolling_timer is
+    port(
+        clk : in std_logic;
+        rst : in std_logic;
+        cnt_start : in std_logic;
+        cnt_done : out std_logic;
+        cnt_value : in std_logic_vector(31 downto 0)
+    );
+end entity scrolling_timer;
+
+architecture Behavioral of scrolling_timer is
+
+	signal counter : std_logic_vector(31 downto 0);
+    signal done : std_logic;
+    signal counting : std_logic;
+    signal value : std_logic_vector(31 downto 0);
+
+begin
+
+	process(clk)
+	begin
+		if clk'event and clk='1' then
+			if rst = '1' then
+				counter <= x"00000000";
+				done <= '0';
+				counting <= '0';
+			else
+			    value <= cnt_value;
+                done <= '0';
+
+				if counter = value and counting = '1' then
+                    counter <= x"00000000";
+                    done <= '1';
+                    counting <= '0';
+                elsif counting = '1' then
+                    counter <= std_logic_vector(unsigned(counter) + 1);
+                elsif counting = '0' and cnt_start = '1' then
+                    counting <= '1';
+                end if;
+			end if;
+		end if;
+	end process;
+
+    cnt_done <= done;
+
+end Behavioral;
diff --git a/soc/testbench/scrolling_timer_tb.vhd b/soc/testbench/scrolling_timer_tb.vhd
new file mode 100644
index 0000000..95f31ff
--- /dev/null
+++ b/soc/testbench/scrolling_timer_tb.vhd
@@ -0,0 +1,77 @@
+-- See the file "LICENSE" for the full license governing this code. --
+LIBRARY ieee;
+USE ieee.std_logic_1164.ALL;
+USE ieee.numeric_std.ALL;
+
+LIBRARY work;
+USE work.lt16soc_peripherals.ALL;
+
+ENTITY scrolling_timer_tb IS
+END ENTITY;
+
+ARCHITECTURE sim OF scrolling_timer_tb IS
+
+    constant CLK_PERIOD : time := 10 ns;
+
+    signal rst : std_logic;
+    signal clk : std_logic := '0';
+
+	signal cnt_start : std_logic := '0';
+    signal cnt_done : std_logic := '0';
+    signal cnt_value : std_logic_vector(31 downto 0) := x"00000000";
+
+    component scrolling_timer is
+        port(
+            clk : in std_logic;
+            rst : in std_logic;
+            cnt_start : in std_logic;
+            cnt_done : out std_logic;
+            cnt_value : in std_logic_vector(31 downto 0)
+        );
+    end component;
+
+BEGIN
+
+	timer: scrolling_timer
+        port map(
+			clk => clk,
+            rst => rst,
+            cnt_start => cnt_start,
+            cnt_done => cnt_done,
+            cnt_value => cnt_value
+    );
+
+    clk_gen: process
+	begin
+		clk	<= not clk;
+		wait for CLK_PERIOD/2;
+	end process clk_gen;
+
+	stimuli: process
+	begin
+        rst <= '1';
+        wait for CLK_PERIOD;
+        rst <= '0';
+
+        wait for CLK_PERIOD*3;
+
+        cnt_value <= x"00000100";
+        cnt_start <= '1';
+        
+        wait for CLK_PERIOD;
+        cnt_start <= '0';
+
+		wait for CLK_PERIOD * 300;
+
+        cnt_value <= x"0000000A";
+        cnt_start <= '1';
+        
+        wait for CLK_PERIOD;
+        cnt_start <= '0';
+        
+        wait for CLK_PERIOD * 15;
+
+		assert false report "Simulation terminated!" severity failure;
+	end process stimuli;
+
+END ARCHITECTURE;