entity ch_02_01 is

end entity ch_02_01;


----------------------------------------------------------------


architecture test of ch_02_01 is
begin


  section_2_1_a : process is

    -- code from book:

    constant number_of_bytes : integer := 4;
    constant number_of_bits : integer := 8 * number_of_bytes;
    constant e : real := 2.718281828;
    constant prop_delay : time := 3 ns;
    constant size_limit, count_limit : integer := 255;

    --

    variable index : integer := 0;
    variable sum, average, largest : real;
    variable start, finish : time := 0 ns; 

    -- end of code from book

  begin
    wait;
  end process section_2_1_a;


  ----------------


  section_2_1_b : process is

    -- code from book:

    variable start : time := 0 ns; 
    variable finish : time := 0 ns; 

    -- end of code from book

    variable program_counter : integer;
    variable index : integer;

  begin

    -- code from book:

    program_counter := 0;
    index := index + 1;

    -- end of code from book

    wait;
  end process section_2_1_b;


  ----------------


  section_2_2_a : process is

    -- code from book:

    type apples is range 0 to 100;
    type oranges is range 0 to 100;

    --

    type day_of_month is range 0 to 31;
    type year is range 0 to 2100;

    variable today : day_of_month := 9;
    variable start_year : year := 1987;

    --

    constant number_of_bits : integer := 32;
    type bit_index is range 0 to number_of_bits - 1;

    --

    type set_index_range is range 21 downto 11;
    type mode_pos_range is range 5 to 7;
    variable set_index : set_index_range;
    variable mode_pos : mode_pos_range;

    --

    type input_level is range -10.0 to +10.0;
    type probability is range 0.0 to 1.0;

    --

    variable input_A : input_level;

    -- end of code from book

  begin

    -- code from book:

    -- error: Incompatible types for assignment
    -- start_year := today;

    -- end of code from book

    wait;
  end process section_2_2_a;


  ----------------


  section_2_2_b : process is

    -- code from book:

    type resistance is range 0 to 1E9
      units
        ohm;
      end units resistance;

    -- end of code from book

  begin
    wait;
  end process section_2_2_b;


  ----------------


  section_2_2_c : process is

    -- code from book:

    type resistance is range 0 to 1E9
      units
        ohm;
        kohm = 1000 ohm;
        Mohm = 1000 kohm;
      end units resistance;

    -- end of code from book

  begin
    wait;
  end process section_2_2_c;


  ----------------


  section_2_2_d : process is

    -- code from book:

    type length is range 0 to 1E9
      units
        um;			-- primary unit: micron
        mm = 1000 um;		-- metric units
        m = 1000 mm;
        inch = 25400 um;        -- imperial units
        foot = 12 inch;
      end units length;

    -- end of code from book

  begin
    wait;
  end process section_2_2_d;


  ----------------


  section_2_2_e : process is

    -- code from book:

    -- type time is range implementation_defined
    type time is range integer'low to integer'high
      units
        fs;
        ps = 1000 fs;
        ns = 1000 ps;
        us = 1000 ns;
        ms = 1000 us;
        sec = 1000 ms;
        min = 60 sec;
        hr = 60 min;
      end units;

    -- end of code from book

  begin
    wait;
  end process section_2_2_e;


  ----------------


  section_2_2_f : process is

    -- code from book:

    type alu_function is (disable, pass, add, subtract, multiply, divide);

    --

    type octal_digit is ('0', '1', '2', '3', '4', '5', '6', '7');

    --

    variable alu_op : alu_function;
    variable last_digit : octal_digit := '0';

    --

    type logic_level is (unknown, low, undriven, high);
    variable control : logic_level;
    type water_level is (dangerously_low, low, ok);
    variable water_sensor : water_level;

    -- end of code from book

  begin

    -- code from book:

    alu_op := subtract;
    last_digit := '7';

    --

    control := low;
    water_sensor := low;

    -- end of code from book

    wait;
  end process section_2_2_f;


  ----------------


  section_2_2_g : process is

    -- code from book:

    type severity_level is (note, warning, error, failure);
    type file_open_status is (open_ok, status_error, name_error, mode_error);
    type file_open_kind is (read_mode, write_mode, append_mode);

    -- end of code from book

  begin
    wait;
  end process section_2_2_g;


  ----------------


  section_2_2_g1 : process is

    -- code from book:

    type character is (
      nul, soh,  stx,  etx,  eot,  enq,  ack,  bel,
      bs,  ht,  lf,  vt,  ff,  cr, so, si,
      dle,  dc1,  dc2,  dc3,  dc4,  nak,  syn,  etb,
      can,  em,  sub,  esc,  fsp,  gsp,  rsp,  usp,
      ' ',  '!',  '"',  '#',  '$',  '%',  '&',  ''',
      '(',  ')',  '*',  '+',  ',',  '-',  '.',  '/',
      '0',  '1',  '2',  '3',  '4',  '5',  '6',  '7',
      '8',  '9',  ':',  ';',  '<',  '=',  '>',  '?',
      '@',  'A',  'B',  'C',  'D',  'E',  'F',  'G',
      'H',  'I',  'J',  'K',  'L',  'M',  'N',  'O',
      'P',  'Q',  'R',  'S',  'T',  'U',  'V',  'W',
      'X',  'Y',  'Z',  '[',  '\',  ']',  '^',  '_', 
      '`',  'a',  'b',  'c',  'd',  'e',  'f',  'g',
      'h',  'i',  'j',  'k',  'l',  'm',  'n',  'o',
      'p',  'q',  'r',  's',  't',  'u',  'v',  'w',
      'x',  'y',  'z',  '{',  '|',  '}',  '~',  DEL,
      c128,  c129,  c130,  c131,  c132,  c133,  c134,  c135,
      c136,  c137,  c138,  c139,  c140,  c141,  c142,  c143,
      c144,  c145,  c146,  c147,  c148,  c149,  c150,  c151,
      c152,  c153,  c154,  c155,  c156,  c157,  c158,  c159,
      ' ',  '¡',  '¢',  '£',  '¤',  '¥',  '¦',  '§',
      '¨',  '©',  'ª',  '«',  '¬',  '­',  '®',  '¯',
      '°',  '±',  '²',  '³',  '´',  'µ',  '¶',  '·',
      '¸',  '¹',  'º',  '»',  '¼',  '½',  '¾',  '¿',
      'À',  'Á',  'Â',  'Ã',  'Ä',  'Å',  'Æ',  'Ç',
      'È',  'É',  'Ê',  'Ë',  'Ì',  'Í',  'Î',  'Ï',
      'Ð',  'Ñ',  'Ò',  'Ó',  'Ô',  'Õ',  'Ö',  '×',
      'Ø',  'Ù',  'Ú',  'Û',  'Ü',  'Ý',  'Þ',  'ß',
      'à',  'á',  'â',  'ã',  'ä',  'å',  'æ',  'ç',
      'è',  'é',  'ê',  'ë',  'ì',  'í',  'î',  'ï',
      'ð',  'ñ',  'ò',  'ó',  'ô',  'õ',  'ö',  '÷',
      'ø',  'ù',  'ú',  'û',  'ü',  'ý',  'þ',  'ÿ');

    -- end of code from book

  begin
    wait;
  end process section_2_2_g1;


  ----------------


  section_2_2_h : process is

    -- code from book:

    variable cmd_char, terminator : character;

    -- end of code from book

  begin

    -- code from book:

    cmd_char := 'P';
    terminator := cr;

    -- end of code from book

    wait;
  end process section_2_2_h;


  ----------------


  section_2_2_i : process is

    -- code from book:

    type boolean is (false, true);

    --

    type bit is ('0', '1');

    -- end of code from book

  begin
    wait;
  end process section_2_2_i;


  ----------------


  section_2_2_j : process is

    variable write_enable_n, select_reg_n, write_reg_n : bit;

  begin

    -- code from book:

    write_reg_n := not ( not write_enable_n and not select_reg_n );

    -- end of code from book

    wait;
  end process section_2_2_j;


  ----------------


  section_2_2_k : process is

    -- code from book:

    type std_ulogic is ( 'U',	-- Uninitialized
                         'X',	-- Forcing Unknown
                         '0',	-- Forcing zero
                         '1',	-- Forcing one
                         'Z',	-- High Impedance
                         'W',	-- Weak Unknown
                         'L',	-- Weak zero
                         'H',	-- Weak one
                         '-' );	-- Don't care

    -- end of code from book

  begin
    wait;
  end process section_2_2_k;


  ----------------


  section_2_3_a : process is

    -- code from book:

    subtype small_int is integer range -128 to 127;

    --

    variable deviation : small_int;
    variable adjustment : integer;

    --

    subtype bit_index is integer range 31 downto 0;

    -- end of code from book

  begin

    deviation := 0;
    adjustment := 0;

    -- code from book:

    deviation := deviation + adjustment;

    -- end of code from book

    wait;
  end process section_2_3_a;


  ----------------


  section_2_3_b : process is

    constant highest_integer : integer := integer'high;

    constant highest_time : time := time'high;

    -- code from book:

    subtype natural is integer range 0 to highest_integer;
    subtype positive is integer range 1 to highest_integer;

    --

    subtype delay_length is time range 0 fs to highest_time;

    -- end of code from book

  begin
     wait;
 end process section_2_3_b;


  ----------------


  section_2_3_c : process is

    -- code from book:

    type logic_level is (unknown, low, undriven, high);
    type system_state is (unknown, ready, busy);

    --

    subtype valid_level is logic_level range low to high;

    -- end of code from book

  begin
    wait;
  end process section_2_3_c;


  ----------------


  section_2_4_a : process is

    -- code from book:

    type resistance is range 0 to 1E9
      units
        ohm;
        kohm = 1000 ohm;
        Mohm = 1000 kohm;
      end units resistance;

    type set_index_range is range 21 downto 11;

    type logic_level is (unknown, low, undriven, high);

    -- end of code from book

  begin

    -- output from vsim: "2000"
    report resistance'image(2 kohm);

    -- code from book:

    assert resistance'left = 0 ohm;
    assert resistance'right = 1E9 ohm;
    assert resistance'low = 0 ohm;
    assert resistance'high = 1E9 ohm;
    assert resistance'ascending = true;
    assert resistance'image(2 kohm) = "2000 ohm";
    assert resistance'value("5 Mohm") = 5_000_000 ohm;

    assert set_index_range'left = 21;
    assert set_index_range'right = 11;
    assert set_index_range'low = 11;
    assert set_index_range'high = 21;
    assert set_index_range'ascending = false;
    assert set_index_range'image(14) = "14";
    assert set_index_range'value("20") = 20;

    assert logic_level'left = unknown;
    assert logic_level'right = high;
    assert logic_level'low = unknown;
    assert logic_level'high = high;
    assert logic_level'ascending = true;
    assert logic_level'image(undriven) = "undriven";
    assert logic_level'value("Low") = low;

    --

    assert logic_level'pos(unknown) = 0;
    assert logic_level'val(3) = high;
    assert logic_level'succ(unknown) = low;
    assert logic_level'pred(undriven) = low;

    --

    assert time'pos(4 ns) = 4_000_000;

    -- end of code from book

    wait;
  end process section_2_4_a;


  ----------------


  section_2_4_b : process is

    -- code from book:

    type length is range integer'low to integer'high
      units
        mm;
      end units length;

    type area is range integer'low to integer'high
      units
        square_mm;
      end units area;

    --

    variable L1, L2 : length;
    variable A : area;

    -- end of code from book

  begin

    -- code from book:

    -- error: No feasible entries for infix op: "*"
    -- A := L1 * L2;      -- this is incorrect

    --

    A := area'val( length'pos(L1) * length'pos(L2) );

    -- end of code from book

    wait;
  end process section_2_4_b;


  ----------------


  section_2_4_c : process is

    -- code from book:

    type opcode is (nop, load, store, add, subtract, negate, branch, halt);
    subtype arith_op is opcode range add to negate;

    -- end of code from book

  begin

    -- code from book:

    assert arith_op'base'left = nop;
    assert arith_op'base'succ(negate) = branch;

    -- end of code from book

    wait;
  end process section_2_4_c;


end architecture test;