6 files changed, 209 insertions, 0 deletions
diff --git a/examples/icestick/uart/README.md b/examples/icestick/uart/README.md
new file mode 100755
index 0000000..b53def6
--- /dev/null
+++ b/examples/icestick/uart/README.md
@@ -0,0 +1,11 @@
+# icestick-uart
+Simple UART sender and receiver for the lattice icestick. It echoes every received word back.
+Configuration: 115200 8N1
+
+## Repository structure
+- hdl: Contains the hardware design.
+- syn: Contains the scripts and constraints for synthesis.
+
+## Usage
+- `cd syn && ./synth.sh`
+- configure and open putty or another serial terminal and type something
+\ No newline at end of file
diff --git a/examples/icestick/uart/hdl/uart_rx.vhd b/examples/icestick/uart/hdl/uart_rx.vhd
new file mode 100755
index 0000000..5f488cc
--- /dev/null
+++ b/examples/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;
diff --git a/examples/icestick/uart/hdl/uart_top.vhd b/examples/icestick/uart/hdl/uart_top.vhd
new file mode 100755
index 0000000..889a3a0
--- /dev/null
+++ b/examples/icestick/uart/hdl/uart_top.vhd
@@ -0,0 +1,49 @@
+library ieee;
+  use ieee.std_logic_1164.all;
+
+entity uart_top is
+  generic (
+    C_BITS : integer := 8
+  );
+  port (
+    isl_clk    : in std_logic;
+    isl_data_n : in std_logic;
+    osl_data_n : out std_logic;
+    osl_ready  : out std_logic
+  );
+end uart_top;
+
+architecture behavioral of uart_top is
+  constant C_QUARTZ_FREQ : integer := 12000000; -- Hz
+  constant C_BAUDRATE : integer := 115200; -- words / s
+  constant C_CYCLES_PER_BIT : integer := C_QUARTZ_FREQ / C_BAUDRATE;
+
+  signal sl_valid_out_tx : std_logic := '0';
+  signal slv_data_out_tx : std_logic_vector(C_BITS-1 downto 0) := (others => '0');
+
+begin
+  i_uart_rx: entity work.uart_rx
+  generic map (
+    C_BITS => C_BITS,
+    C_CYCLES_PER_BIT => C_CYCLES_PER_BIT
+  )
+  port map (
+    isl_clk => isl_clk,
+    isl_data_n => isl_data_n,
+    oslv_data => slv_data_out_tx,
+    osl_valid => sl_valid_out_tx
+  );
+
+  i_uart_tx: entity work.uart_tx
+  generic map (
+    C_BITS => C_BITS,
+    C_CYCLES_PER_BIT => C_CYCLES_PER_BIT
+  )
+  port map (
+    isl_clk => isl_clk,
+    isl_valid => sl_valid_out_tx,
+    islv_data => slv_data_out_tx,
+    osl_data_n => osl_data_n,
+    osl_ready => osl_ready
+  );
+end behavioral;
+\ No newline at end of file
diff --git a/examples/icestick/uart/hdl/uart_tx.vhd b/examples/icestick/uart/hdl/uart_tx.vhd
new file mode 100755
index 0000000..b6c5800
--- /dev/null
+++ b/examples/icestick/uart/hdl/uart_tx.vhd
@@ -0,0 +1,62 @@
+library ieee;
+  use ieee.std_logic_1164.all;
+
+entity uart_tx is
+  generic (
+    -- TODO: range in submodules is not yet supported by synthesis
+    --       it would be useful to limit between 5 to 8
+    C_BITS           : integer := 8;
+    C_CYCLES_PER_BIT : integer := 104
+  );
+  port (
+    isl_clk    : in std_logic;
+    isl_valid  : in std_logic;
+    islv_data  : in std_logic_vector(C_BITS-1 downto 0);
+    osl_ready  : out std_logic;
+    osl_data_n : out std_logic
+  );
+end entity uart_tx;
+
+architecture rtl of uart_tx 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+2 := 0;
+
+  signal slv_data : std_logic_vector(C_BITS downto 0) := (others => '0');
+
+  type t_state is (IDLE, INIT, SEND);
+  signal state : t_state;
+
+begin
+  process(isl_clk)
+  begin
+    if rising_edge(isl_clk) then
+      case state is
+        when IDLE =>
+          if isl_valid = '1' then
+            state <= INIT;
+          end if;
+
+        when INIT =>
+          int_cycle_cnt <= 0;
+          int_bit_cnt <= 0;
+          slv_data <= islv_data & '1';
+          state <= SEND;
+        
+        when SEND =>
+          if int_cycle_cnt < C_CYCLES_PER_BIT-1 then
+            int_cycle_cnt <= int_cycle_cnt+1;
+          elsif int_bit_cnt < C_BITS+1 then
+            int_cycle_cnt <= 0;
+            int_bit_cnt <= int_bit_cnt+1;
+            slv_data <= '0' & slv_data(slv_data'LEFT downto 1);
+          else
+            state <= IDLE;
+          end if;
+
+      end case;
+    end if;
+  end process;
+
+  osl_ready <= '1' when state = IDLE else '0';
+  osl_data_n <= not slv_data(0); -- low active
+end architecture rtl;
+\ No newline at end of file
diff --git a/examples/icestick/uart/syn/constraints/uart.pcf b/examples/icestick/uart/syn/constraints/uart.pcf
new file mode 100755
index 0000000..e3e5016
--- /dev/null
+++ b/examples/icestick/uart/syn/constraints/uart.pcf
@@ -0,0 +1,6 @@
+# FTDI Port B UART
+set_io osl_data_n 8  # UART TX
+set_io isl_data_n 9  # UART RX
+
+# 12 MHz clock
+set_io isl_clk 21
diff --git a/examples/icestick/uart/syn/synth.sh b/examples/icestick/uart/syn/synth.sh
new file mode 100755
index 0000000..884f1b6
--- /dev/null
+++ b/examples/icestick/uart/syn/synth.sh
@@ -0,0 +1,15 @@
+set -e
+
+ROOT="$(pwd)/.."
+
+rm -rf build
+mkdir -p build
+cd build
+
+ghdl -a "$ROOT"/hdl/uart_rx.vhd
+ghdl -a "$ROOT"/hdl/uart_tx.vhd
+ghdl -a "$ROOT"/hdl/uart_top.vhd
+yosys -m ghdl -p 'ghdl uart_top; synth_ice40 -json uart_top.json'
+nextpnr-ice40 --hx1k --json uart_top.json --pcf ../constraints/uart.pcf --asc uart_top.asc --pcf-allow-unconstrained
+icepack uart_top.asc uart_top.bin
+iceprog uart_top.bin