Icestick uart (#37)

* added UART example for the icestick

* extended testsuite by the UART example

1 files changed, 66 insertions, 0 deletions

diff --git a/icestick/uart/hdl/uart_rx.vhd b/icestick/uart/hdl/uart_rx.vhd
new file mode 100755
index 0000000..5f488cc
--- /dev/null
+++ b/icestick/uart/hdl/uart_rx.vhd
@@ -0,0 +1,66 @@
+library ieee;
+  use ieee.std_logic_1164.all;
+
+entity uart_rx is
+  generic (
+    C_BITS           : integer := 8;
+    C_CYCLES_PER_BIT : integer := 104
+  );
+  port (
+    isl_clk    : in std_logic;
+    isl_data_n : in std_logic;
+    oslv_data  : out std_logic_vector(C_BITS-1 downto 0);
+    osl_valid  : out std_logic
+  );
+end entity uart_rx;
+
+architecture rtl of uart_rx is
+  signal int_cycle_cnt : integer range 0 to C_CYCLES_PER_BIT-1 := 0;
+  signal int_bit_cnt : integer range 0 to C_BITS+1 := 0;
+
+  signal slv_data : std_logic_vector(C_BITS-1 downto 0) := (others => '0');
+  signal sl_valid : std_logic := '0';
+
+  type t_state is (IDLE, INIT, RECEIVE);
+  signal state : t_state;
+
+begin
+  process(isl_clk)
+  begin
+    if rising_edge(isl_clk) then
+      case state is
+        when IDLE =>
+          sl_valid <= '0';
+          if isl_data_n = '0' then
+            -- wait for the start bit
+            state <= INIT;
+          end if;
+        
+        when INIT =>
+          int_cycle_cnt <= C_CYCLES_PER_BIT / 2;
+          int_bit_cnt <= 0;
+          state <= RECEIVE;
+
+        when RECEIVE =>
+          if int_bit_cnt < C_BITS+1 then
+            if int_cycle_cnt < C_CYCLES_PER_BIT-1 then
+              int_cycle_cnt <= int_cycle_cnt+1;
+            else
+              -- receive data bits
+              int_cycle_cnt <= 0;
+              int_bit_cnt <= int_bit_cnt+1;
+              slv_data <= not isl_data_n & slv_data(slv_data'LEFT downto 1); -- low active
+            end if;
+          elsif isl_data_n = '1' then
+            -- wait for the stop bit
+            sl_valid <= '1';
+            state <= IDLE;
+          end if;
+
+      end case;
+    end if;
+  end process;
+
+  oslv_data <= slv_data;
+  osl_valid <= sl_valid;
+end architecture rtl;