VHDL File I/O - File read write code example

     Here we present the VHDL File I/O syntax and examples.

     This is very useful in handling file i/o for processing signals, images into VHDL codes.

VHDL File operations:

• File open
• File read/write
• File close

Libraries: 
The file i/o procedures and commands are under IEEE -> STD_LOGIC_TEXTIO

library IEEE;
use IEEE.STD_LOGIC_TEXTIO.ALL;

File open syntax:

file <FILEPOINTER> : text is in "<FILENAME>";

File Read Syntax:

procedure READLINE(file F: TEXT; L: out LINE);
procedure READ(L: inout LINE; value: out bit);
-- line serves as a buffer for the data to be written/read  into/from  a file

    variable <inline>: line;
    variable <dataread> : real;

    readline(<infileptr>, <inline>);
    read(<inline>, <dataread>);

Then this real value can be converted into required datatype.

File Write Syntax:

procedure WRITELINE(file F: TEXT; L: inout LINE);
procedure WRITE(L: inout LINE; value: out bit);

    variable <inline>: line;
    variable <datas> : real;
    variable <dataint> : integer;

   write(<inline>, <datas>);   --writes real
   writeline(<infileptr>, <inline>);

   write(<inline>, <dataint>);  -- writes integer
   writeline(<infileptr>, <inline>);

For checking current line as end-of-file:

endfile(<fileptr>);

   
For writing string & bitvector:

WRITE (buf, string’("hello"));
WRITELINE(fileptr,buf);
WRITE (buf, bit_vector’("010111"));
WRITELINE(fileptr,buf);

Example for file read & write as a PROCESS:

din:STD_LOGIC_VECTOR(7 downto 0);
d1,intt,linenumber: integer;
dreal:real;

reading : process
    file infile : text is in "file1.txt"; --declare input file 1987
    variable inline: line; --line number declaration
    variable dataread1 : real;
    begin
        wait until clk = '1' and clk'event;
            if (not (endfile(infile)) then
                    readline(infile, inline);
                    read(inline, dataread1);
                    d1 <=integer(dataread1);
            else   
                endoffile <='1'; --set signal to tell end of file read file is reached.
        end if;
    end process reading;

writing : process
    file outfile : text is out "outimgvhdl.txt";
    variable buff_out : line; --line number declaration
    begin
        wait until clk = '1' and clk'event;
        if(endoffile='0') then --if the file end is not reached.
            write(buff_out, intt);             --writes integer
            writeline(outfile, buff_out);

            write(buff_out, din);             --writes STD_LV
            writeline(outfile, buff_out);

            write(buff_out, dreal);             --writes real data (float)
            writeline(outfile, buff_out);
          end if;   
            linenumber <= linenumber + 1;
        else
            null;
        end if;
    end process writing;

 

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