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
• A file class needs to be defined before it can be used.
file_type_defn <= type file_type_name is file of type_mark ;
type integer _file is file of integer ;
• Once defined, a file object can be declared.
file_decl <= file id { , …} : subtype_indication
[ [ open file_open_kind ] is string_expr ;
type file_open_kind is
(read_mode, write_mode, append_mode);
file table: integer _file open read_mode is “table.dat” ;
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.
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;
Example
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
VHDL provides two implicit procedures:
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);
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