c4m/vhdl/jtag/c4m_jtag_idblock.vhdl

   1 -- The JTAG id and bypass handling block
   2
   3 library ieee;
   4 use ieee.std_logic_1164.ALL;
   5
   6 use work.c4m_jtag.ALL;
   7
   8 entity c4m_jtag_idblock is
   9   generic (
  10     IR_WIDTH:           integer := 2;
  11
  12     MANUFACTURER:       std_logic_vector(10 downto 0) := "10001111111";
  13     PART_NUMBER:        std_logic_vector(15 downto 0) := "0000000000000001";
  14     VERSION:            std_logic_vector(3 downto 0) := "0000"
  15   );
  16   port (
  17     -- needed TAP signals
  18     TCK:        in std_logic;
  19     TDI:        in std_logic;
  20     TDO:        out std_logic;
  21     TDO_EN:     out std_logic := '0';
  22
  23     -- The instruction
  24     IR:         in std_logic_vector(IR_WIDTH-1 downto 0);
  25
  26     -- actions
  27     CAPTURE:    in std_logic;
  28     SHIFT:      in std_logic;
  29     UPDATE:     in std_logic
  30   );
  31 end c4m_jtag_idblock;
  32
  33 architecture rtl of c4m_jtag_idblock is
  34   constant IDCODE:      std_logic_vector(31 downto 0) := VERSION & PART_NUMBER & MANUFACTURER & "1";
  35
  36   signal SR_ID:         std_logic_vector(31 downto 0);
  37   signal EN_TDO:        boolean;
  38
  39   constant CMD_IDCODE:  std_logic_vector(IR_WIDTH-1 downto 0) := c4m_jtag_cmd_idcode(IR_WIDTH);
  40   constant CMD_BYPASS:  std_logic_vector(IR_WIDTH-1 downto 0) := c4m_jtag_cmd_bypass(IR_WIDTH);
  41 begin
  42   process (TCK)
  43   begin
  44     if rising_edge(TCK) then
  45       if CAPTURE = '1' then
  46         SR_ID <= IDCODE;
  47       elsif SHIFT = '1' then
  48         if IR = CMD_IDCODE then
  49           SR_ID(30 downto 0) <= SR_ID(31 downto 1);
  50           SR_ID(31) <= TDI;
  51         elsif IR = CMD_BYPASS then
  52           SR_ID(0) <= TDI;
  53         end if;
  54       end if;
  55     end if;
  56   end process;
  57
  58   TDO <= SR_ID(0) when EN_TDO else
  59          '0';
  60   EN_TDO <= SHIFT = '1' and (IR = CMD_IDCODE or IR = CMD_BYPASS);
  61   TDO_EN <= '1' when EN_TDO else
  62             '0';
  63 end rtl;