----------------------------------------------------------------------------------
-- Module Name:    tb_top
-- Project Name:   AD7766_prj
-- Description:
--   Сквозной тест: модель AD7766 -> top -> UART -> разбор кадра в тестбенче.
--   Модель выдаёт группами по DECIM одинаковых слов, поэтому усреднённый
--   отсчёт обязан в точности совпасть со значением группы. Проверяются
--   разрядность, знак, порядок байт, CRC и счётчик кадров.
----------------------------------------------------------------------------------
library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
use std.env.all;

entity tb_top is
  generic (
    FRAMES : integer := 2 -- сколько кадров проверяем, переопределяется -gFRAMES=N
  );
end entity tb_top;

architecture sim of tb_top is

  constant CLK_T : time    := 20 ns;
  constant BAUD  : integer := 921600;
  constant BIT_T : time    := 1 sec / BAUD;
  constant DECIM : integer := 10;
  constant SPF   : integer := 50; -- отсчётов в кадре

  constant PAYLOAD_LEN : integer := 2 + 1 + SPF * 3; -- CNT + STATUS + DATA

  signal clk : std_logic := '0';
  signal run : boolean   := true;

  signal adc_sdo     : std_logic;
  signal adc_drdy    : std_logic;
  signal adc_sclk    : std_logic;
  signal adc_mclk    : std_logic;
  signal adc_sdi     : std_logic;
  signal adc_cs_n    : std_logic;
  signal adc_sync_pd : std_logic;
  signal uart_tx     : std_logic;
  signal led         : std_logic;

  signal next_word : std_logic_vector(23 downto 0);
  signal word_tick : std_logic;
  signal word_idx  : integer := 0;

  type byte_arr_t is array (natural range <>) of std_logic_vector(7 downto 0);

  -- Значения групп: крайние точки шкалы, единицы младшего разряда и оба знака
  function grp_value(g : integer) return signed is
    variable v : integer;
  begin
    case g mod 8 is
      when 0      => v := 0;
      when 1      => v := 8388607;  -- +полная шкала
      when 2      => v := - 8388608; -- -полная шкала
      when 3      => v := 1;
      when 4      => v := - 1;
      when 5      => v := 5592405;  -- 0x555555
      when 6      => v := - 5592406; -- 0xAAAAAA как знаковое
      when others => v := 1193046;  -- 0x123456
    end case;
    return to_signed(v, 24);
  end function;

  function crc16_upd(crc : std_logic_vector(15 downto 0);
    d                    : std_logic_vector(7 downto 0))
    return std_logic_vector is
    variable c  : std_logic_vector(15 downto 0) := crc;
    variable fb : std_logic;
  begin
    for i in 7 downto 0 loop
      fb := c(15) xor d(i);
      c  := c(14 downto 0) & '0';
      if fb = '1' then
        c := c xor x"1021";
      end if;
    end loop;
    return c;
  end function;

  procedure get_byte(signal rx : in std_logic;
    b                          : out std_logic_vector(7 downto 0)) is
    variable v : std_logic_vector(7 downto 0);
  begin
    wait until rx = '0'; -- фронт старт-бита
    wait for BIT_T / 2;
    assert rx = '0' report "start bit not confirmed" severity error;
    for i in 0 to 7 loop
      wait for BIT_T;
      v(i) := rx;
    end loop;
    wait for BIT_T;
    assert rx = '1' report "stop bit not at expected position" severity error;
    b := v;
  end procedure;

begin

  clk <= not clk after CLK_T / 2 when run else '0';

  next_word <= std_logic_vector(grp_value(word_idx / DECIM));

  word_cnt_proc : process
  begin
    wait until rising_edge(word_tick);
    word_idx <= word_idx + 1;
  end process word_cnt_proc;

  dut : entity work.Top(Behavioral)
    generic map(
      SYS_CLK_HZ => 50_000_000,
      BAUD_RATE  => BAUD
    )
    port map
    (
      clk         => clk,
      ADC_SDO     => adc_sdo,
      ADC_DRDY    => adc_drdy,
      ADC_SCLK    => adc_sclk,
      ADC_MCLK    => adc_mclk,
      ADC_SDI     => adc_sdi,
      ADC_CS_N    => adc_cs_n,
      ADC_SYNC_PD => adc_sync_pd,
      UART_TX     => uart_tx,
      LED         => led
    );

  adc : entity work.ad7766_model(model)
    port map
    (
      mclk      => adc_mclk,
      sync_pd_n => adc_sync_pd,
      cs_n      => adc_cs_n,
      sclk      => adc_sclk,
      next_word => next_word,
      sdo       => adc_sdo,
      drdy      => adc_drdy,
      word_tick => word_tick
    );

  check_proc : process
    variable b        : std_logic_vector(7 downto 0);
    variable prev     : std_logic_vector(7 downto 0) := (others => '0');
    variable pl       : byte_arr_t(0 to PAYLOAD_LEN - 1);
    variable crc      : std_logic_vector(15 downto 0);
    variable crc_rx   : std_logic_vector(15 downto 0);
    variable cnt_rx   : integer;
    variable got      : signed(23 downto 0);
    variable want     : signed(23 downto 0);
    variable errors   : integer := 0;
    variable frame_no : integer := 0;
  begin
    report "start: waiting for first frame";

    while frame_no < FRAMES loop

      -- Ищем SYNC A5 5A, как это будет делать приёмник на ПК
      loop
        get_byte(uart_tx, b);
        exit when prev = x"A5" and b = x"5A";
        prev := b;
      end loop;
      prev := (others => '0');

      for i in 0 to PAYLOAD_LEN - 1 loop
        get_byte(uart_tx, b);
        pl(i) := b;
      end loop;
      get_byte(uart_tx, b);
      crc_rx(15 downto 8) := b;
      get_byte(uart_tx, b);
      crc_rx(7 downto 0) := b;

      crc := x"FFFF";
      for i in 0 to PAYLOAD_LEN - 1 loop
        crc := crc16_upd(crc, pl(i));
      end loop;

      if crc /= crc_rx then
        report "frame " & integer'image(frame_no) & ": CRC mismatch" severity error;
        errors := errors + 1;
      end if;

      cnt_rx := to_integer(unsigned(std_logic_vector'(pl(0) & pl(1))));
      if cnt_rx /= frame_no then
        report "frame " & integer'image(frame_no) & ": FRAME_CNT = " &
          integer'image(cnt_rx) severity error;
        errors := errors + 1;
      end if;

      if pl(2) /= x"00" then
        report "frame " & integer'image(frame_no) & ": STATUS not zero" severity error;
        errors := errors + 1;
      end if;

      for i in 0 to SPF - 1 loop
        got := signed(std_logic_vector'(pl(3 + i * 3) & pl(4 + i * 3) & pl(5 + i * 3)));
        want := grp_value(frame_no * SPF + i);
        if got /= want then
          report "frame " & integer'image(frame_no) & " sample " & integer'image(i) &
            ": got " & integer'image(to_integer(got)) &
            ", want " & integer'image(to_integer(want)) severity error;
          errors := errors + 1;
        end if;
      end loop;

      report "frame " & integer'image(frame_no) & " parsed OK";
      frame_no := frame_no + 1;
    end loop;

    if errors = 0 then
      report "TEST PASSED: frames = " & integer'image(FRAMES) & "";
    else
      report "TEST FAILED: errors = " & integer'image(errors) severity error;
    end if;

    run <= false;
    stop;
  end process check_proc;

end architecture sim;