一个rom程序，编译时总说"std_logic_textio"denoted by prefix"IEEE"must exist in the library,请高手指教
library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_arith.all;
use IEEE.std_logic_textio.all;
library STD;
use STD.textio.all;
------------------------ ENTITY DECLARATION -------------------------
entity mc8051_rom is
generic (c_init_file : string := "mc8051_rom.dua");
port (clk : in std_logic; -- clock signal
reset : in std_logic; -- reset signal
rom_data_o : out std_logic_vector(7 downto 0); -- data output
rom_adr_i : in std_logic_vector(15 downto 0)); -- adresses
end mc8051_rom;
architecture sim of mc8051_rom is
type rom_type is array (65535 downto 0) of bit_vector(7 downto 0);
signal s_init : boolean := false;
begin
------------------------------------------------------------------------------
-- rom_read
------------------------------------------------------------------------------
p_read : process (clk, reset, rom_adr_i)
variable v_loop : integer;
variable v_line : line;
variable v_rom_data : rom_type;
file f_initfile : text is in c_init_file;
begin
if (not s_init) then
v_loop := 0;
while ((not endfile(f_initfile) and (v_loop < 65535))) loop
readline(f_initfile,v_line);
read(v_line,v_rom_data(v_loop));
v_loop := v_loop + 1;
end loop;
s_init <= true;
end if;
if (clk'event and (clk = '1')) then -- rising clock edge
rom_data_o <= to_stdlogicvector(v_rom_data(conv_integer(unsigned(rom_adr_i))));
end if;
end process p_read;
end sim;
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