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--
-- Copyright 2018 Ettus Research, A National Instruments Company
--
-- SPDX-License-Identifier: LGPL-3.0
--
-- Module: bitq_fsm
-- Description: Simple IP to shift bits in/out (primarily for JTAG)
-- bitq_fsm implements the state machine underlying the IP
library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
entity bitq_fsm is
port (
clk : in std_logic;
rstn : in std_logic;
prescalar : in std_logic_vector(7 downto 0);
bit_clk : inout std_logic;
bit_in : in std_logic;
bit_out : inout std_logic;
bit_stb : inout std_logic;
start : in std_logic;
ready : out std_logic;
len : in std_logic_vector(4 downto 0);
wr_data : in std_logic_vector(31 downto 0);
stb_data : in std_logic_vector(31 downto 0);
rd_data : out std_logic_vector(31 downto 0)
);
end bitq_fsm;
architecture arch of bitq_fsm is
type bitq_state_t is (IDLE, LOW, HIGH);
signal bitq_state : bitq_state_t;
signal bit_clk_count : unsigned(7 downto 0);
signal bit_count : unsigned(5 downto 0);
signal bit_out_r : std_logic;
signal bit_stb_r : std_logic;
signal rd_data_r : std_logic_vector(31 downto 0);
begin
rd_data <= rd_data_r;
gen_io : process (bitq_state, bit_count, bit_out_r, bit_stb_r)
begin
case (bitq_state) is
when IDLE =>
bit_clk <= 'Z';
bit_out <= 'Z';
bit_stb <= 'Z';
ready <= '1';
when LOW =>
bit_clk <= '0';
bit_out <= bit_out_r;
bit_stb <= bit_stb_r;
ready <= '0';
when HIGH =>
bit_clk <= '1';
bit_out <= bit_out_r;
bit_stb <= bit_stb_r;
ready <= '0';
when others =>
bit_clk <= 'Z';
bit_out <= 'Z';
bit_stb <= 'Z';
ready <= '1';
end case;
end process;
bit_clk_gen : process (clk)
begin
if rising_edge(clk) then
if (rstn = '0') or (bitq_state = IDLE) or
(bit_clk_count = 0) then
bit_clk_count <= unsigned(prescalar);
elsif (bit_clk_count /= 0) then
bit_clk_count <= bit_clk_count - 1;
end if;
end if;
end process bit_clk_gen;
fsm : process (clk)
begin
if rising_edge(clk) then
if (rstn = '0') then
bitq_state <= IDLE;
bit_count <= to_unsigned(0, bit_count'length);
rd_data_r <= (others => '0');
else
case bitq_state is
when IDLE =>
bit_count <= to_unsigned(0, bit_count'length);
if (start = '1') then
bitq_state <= LOW;
rd_data_r <= (others => '0');
bit_out_r <= wr_data(0);
bit_stb_r <= stb_data(0);
end if;
when LOW =>
if (bit_clk_count = 0) then
rd_data_r(to_integer(bit_count)) <= bit_in;
bit_count <= bit_count + 1;
bitq_state <= HIGH; --Rising edge
end if;
when HIGH =>
if (bit_clk_count = 0) then
if (bit_count > unsigned('0' & len)) then
bitq_state <= IDLE;
else
bit_out_r <= wr_data(to_integer(bit_count));
bit_stb_r <= stb_data(to_integer(bit_count));
bitq_state <= LOW; --Falling edge
end if;
end if;
end case;
end if;
end if;
end process fsm;
end arch;
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