EE295 - ASIC Design With VHDL Class - Fall 1999

Files and I/O

Files are used to store values to apply to designs, initialize design components or compare design outputs.
Often referred to as 'pattern' files because these files may be used for other purposes like supplying
patterns to the ASIC manufacturing  tester.

VHDL provides a package of utility types, file objects, procedures.
VHDL Strives to be a portable language. The file interface is simple and the LRM does not
describe how to impliment physical files so exact details mary vary by product.

Outline:

• File Declarations
• Reading from Files
• Writing to Files
• Explicit Open and Close
• File I/O Status
• Files Declared in SubPrograms
• Text I/O
• Types
• PreDefined Files
• Read Procedures
• Write Procedures:
• Detecting End of File
•  Example of TextIO Read
•  Example of TextIO Write

---

File Declarations

type file_type is file of type_mark ;
 
Declares a file_type
 
example..
 
type bitfile is file of bit_vector ( 0 to 31 ) ;
 

---

VHDL-93
file file_name {,...} : subtype_indication
[[ open file_open_kind_expession ] is string_expression ] ;
type file_open_kind is ( read_mode, write_mode, append_mode );

example..

file p_file : bitfile  is "C:\CLASS\ALU.PAT" ;
 

---

VHDL-87
file file_name {,...} : subtype_indication
[[ open in | out ] is string_expression ] ;
 
Note - This is not Upward Compatable with VHDL-93. Keywords in and  out replaced
with file_open_kind.
Avoid Declaring Multiple File Objects to the Same Physical File.
VHDL Legal But Unpredictable

Reading from Files

Implicitly Declared Routines

procedure read ( file f : file_type; value : out element_type ) ;

function endfile ( file f : file_type )  return boolean ;
 

Example:
 
file p_file : bitfile open read_mode is patterns ;

...

While not( endfile ( p_file ) loop
 

read ( p_file, p ( i ) );
i := i + 1 ;
end loop;
 
Initalizing an Array Using a SubRoutine to Read a File..
 
constant bit_array : bit_vector := read_array ( "C:|CLASS\ALU.PAT", 16 );

Writing to Files

Implicitly Declared Routine

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

Example:

file p_file : bitfile open write_mode is patterns ;

...

For i in p'range loop
 

write ( p_file, p ( i ) );
i := i + 1 ;
end loop;
 

Explicit Open and Close

Files Can Be Opened at Simulation Initialization or Under Explicit Control

PreDefined SubRoutines
 
procedure file_open (  file f : file_type,
external_name :  in string ,
open_kind : in file_open_kind := read_mode ) ;
 
procedure file_close (  file f : file_type ) ;
 
 
Example:
 
file p_file : bitfile  is "C:\CLASS\ALU.PAT" ;

...

procedure file_open (  p_file,

external_name => "C:\CLASS\ALU.PAT ,
open_kind => read_mode ) ;
 

File I/O Status

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

---

file_open_status

open_ok
File Opened Successfully
status_error
File Previously Opened
name_error
read_mode, append_mode - File Does Not Exist
write_mode - Can Not Create File file_name
mode_error
File Exists But Can NotOpened in Specific Mode

Files Declared in SubPrograms

File Objects Declared in an Architecture and Opened
• Open at Simulation Initialization
• Remain Open During Entire Simulation
• Close at Termination of Simulation
 
File Objects Declared in SubPrograms
• Open Upon SubProgram Invocation
• Remain Open Throughout SubPRogram Execution
• Close at Termination of SubRoutine

Text I/O

The LRM specifies a textio package in library std.

Useful utilities for processing text files.

Types:

Type Text is file of String;

Type Line is access String;

Type Side is ( Right, Left );

Subtype Width is Natural;
 

---

PreDefined Files

Input : Text is in "Std_Input";  -- usually mapped to keyboard

Output : Text is out "Std_Output"; --usually mapped to console

---

Read Procedures:

procedure ReadLine ( F : in Text; L : out Line );

procedure Read ( L : inout; Value : out; |Good : out Boolean| );

Read is an Overloaded Procedure Where Value May be of Type:

• Bit, Bit_Vector
• Boolean
• Character
• Integer
• Real
• String
• Time
 
 

---

Write Procedures:

 
procedure WriteLine ( F : out Text; L : out Line );

procedure Write ( L : inout;..

Write is an Overloaded Procedure Where Value May be of Type:

• Bit, Bit_Vector
• Boolean
• Character
• Integer
• Real
• String
• Time

---

Detecting End of File Condition:

VHDL-87 Included

function endfile ( F : in File ) return Boolean;

VHDL-93 Equivalant

L'length = 0
 

---

 Example of TextIO Read Operation:

file p_file : text  open read_mode is "C:\CLASS\ALU.PAT" ;

Begin

Process
Variable l : Line;
Variable b : Bit;
...
Begin
While Not Endfile( f ) Loop
Readline ( p_file, l );
Read ( l, b );
...
End Loop;
End Process;
End Arc;

---

Example of TextIO Write Operation:

file p_file : text  open write_mode is "C:\CLASS\ALU.PAT" ;

Begin

Process
Variable l : Line;
Variable r : Bit_vector ( 31 downto 0 ) ;
...
Begin
For i in r'range  Loop
Write ( l, r ( i ) );
...
Writeline ( p_file, l ). ;
End Loop;
End Process;
End Arc;
 

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