ECE 368 CAD-Based Logic Design

Shantanu Dutt

Lecture 11

File I/O and Textio in VHDL

(courtesy of Karam Chatha, ASU)

Files

• In all the testbenches we created so far, the test stimuli were coded inside each testbench.

• Hence, if we need to change the test stimuli we

need to modify the model or create a new model.

• Input and output files can be used to get around

this problem.

File Definition and Declaration

file_type_defn <= type file_type_name is file of type_mark ;

• A file class needs to be defined before it can be used.

• Once defined, a file object can be declared.

type integer _file is file of integer ;

file_decl <= file id { , …} : subtype_indication

[ [ open file_open_kind ] is string_expr ;

file table: integer _file open read_mode is “table.dat” ;

type file_open_kind is (read_mode, write_mode, append_mode);

File reading

• Given a file definition, VHDL implicitly provides the following subprograms:

type file_type is file of element_type; procedure read ( file f: file_type; value : out element_type; length : out natural); function endfile ( file f: file_type ) return boolean;

If the length of the element is greater than the length of the actual data on the file, it is placed left justified in the element.

Example p1: process is

type bit_vector_file is file of bit_vectors; file vectors: bit_vector_file open read_mode is “vec.dat”; variable next_vector : bit_vector (63 downto 0); variable actual_len: natural;

begin while not endfile(vectors) loop

read (vectors,next_vector,actual_len); if actual_len > next_vector’length then

report “vector too long”; else

for bit_index in 1 to actual_len loop ….

end loop; end if;

end loop; wait;

end process;

File writing

• Given a file definition, VHDL implicitly provides the following subprograms:

type file_type is file of element_type; procedure write ( file f: file_type; value : in element_type);

Problem Description

• Write a process description that writes the data of integer type from an input signal to a file. • Assume that the input signal “s1” is an “in” port of the top level entity. • Assume the file name to be “out.dat”.

Example

P1: process (s1) is type integer_file is file of integer; file out_file: integer_file open write_mode is “out.dat”;

begin write (out_file,s1);

end;

Files in Subprograms

• In all the examples of file I/O thus far, files are opened at the start of simulation, and automatically closed at end of simulation.

• However, for files declared in subprograms, files

are opened and closed at each invocation of the subprogram.

Example

function read_array (file_name: string; len: natural) return integer_vector is

type integer_file is file of integer; file data_file: integer_file open read_mode is file_name; variable result: integer_vector(1 to len); variable index: integer := 1;

begin while not endfile(data_file) and index <= len loop

read(data_file, result(index)); index:= index + 1;

end loop; return result;

end;

File open and close

• In the examples discussed thus far: • we have opened the files at definition. • we have implicitly closed the files.

• VHDL permits explicit opening and closing of

files.

File open and close

procedure file_open (status : out file_open_status; file f: file_type; extern_name: in string; open_kind : in file_open_mode := read_mode); type file_open_status is (open_ok, status_error, name_error, mode_error);

VHDL provides two implicit procedures:

procedure file_close (file f: file_type);

Open errors

status_error: file object previously open and associated with a physical file.

name_error: in read mode indicates file does not exist.

in write mode indicates file cannot be created. in append mode indicates both.

mode_error: indicates file cannot be opened in the specified

mode.

File procedure parameters

procedure read_transform (file f: transform_file; variable transform : out transform_array) is begin

for i in transform’range(1) loop for j in transform’range(2) loop

if endfile(f) then report “unexpected end of file” severity error;

return end if; read (f,transform(i,j));

end loop; end loop;

end;

VHDL does not permit reading or writing of 2-D arrays.

Package textio

• The file that we have created can read only one type of objects.

• The package textio provides useful functions for

reading general text files.

• The package is part of the standard library “std”.

Package textio

type line is access string;

type text is file of string;

type side is (right,left);

subtype width is natural;

file input: text open read_mode is “std_input”;

file output: text open write_mode is “std_output”;

procedure readline (file f: text; L: inout line);

procedure writeline (file f: text; L: inout line);

Using textio procedures

• The type “access” denotes a pointer in VHDL.

• textio works with a pointer to a line of

text or string.

• A pointer is an object that has the starting address

of the line of text.

Pointer String

• “readline” and “writeline” read and write an entire string that is pointed to by the pointer.

textio read procedures procedure read (L : inout line; value: out bit; good: out boolean); procedure read (L : inout line; value: out bit_vector; good: out boolean); procedure read (L : inout line; value: out boolean; good: out boolean); procedure read (L : inout line; value: out character; good: out boolean); procedure read (L : inout line; value: out integer; good: out boolean); procedure read (L : inout line; value: out real; good: out boolean); procedure read (L : inout line; value: out string; good: out boolean); procedure read (L : inout line; value: out time; good: out boolean);

textio read operation • Every read operation that reads a data type other than “character” skips whitespace (ws) characters: Space, Tab. Reading a character does not skip ws chars since they are legitimate characters; if they need to be skipped, then that does need to be done explicitly at the point of the ws character w/ a read: read(L,c), where “c” is of type character. • If the line contains the following items:

fred “cat” 1001010 12 -4.7 a 10 ns

readline(file_id,L); read (L,s); -- L is a string, s is a string read (L,s); read (L,bv); -- bv is a bit_vector read (L,i); -- i is an integer read (L,r); -- r is a real read (L,c); read(L,c); -- c is a character read (L,t); -- t is a time

textio write procedures procedure write (L : inout line; value: in bit; justified: in side := right; field: in width := 0); procedure write (L : inout line; value: in bit_vector; justified: in side := right; field: in width := 0); procedure write (L : inout line; value: in boolean; justified: in side := right; field: in width := 0); procedure write (L : inout line; value: in character; justified: in side := right; field: in width := 0); procedure write (L : inout line; value: in integer; justified: in side := right; field: in width := 0); procedure write (L : inout line; value: in real; justified: in side := right; field: in width := 0); procedure write (L : inout line; value: in string; justified: in side := right; field: in width := 0); procedure write (L : inout line; value: in time; justified: in side := right; field: in width; unit: in time:= ns);

textio write operation

write (L,i,left,5); -- L is a line, i = 45 write (L,’ ‘); write (L,i,right,5); write (L,’ ‘); write (L,”fred”); write (L,’ ‘); write (L,”101”); write (L,’ ‘); write (L,r,left,3); -- r = 3.14159 write (L,’ ‘); write (L,t,left,0,ms); -- t = 23 micro secs writeline(file_id,L);

45bbb bbb45 fred 101 3.1 0.023 ms