1 H ardware D escription L anguages Basic Input/Output

2 File Objects VHDL objects: Signals, Variables, Constants, Files Files provides an interface between the VHDL programs and the host environment VHDL Program file: type declaration operations

3 Basic I/O Operations File Type and Declaration Opening and Closing a File of a specified type Reading and Writing from a file A very useful example of the application of file I/O is the construction of testbenches Example: the testbench reads test inputs from a file, applies them to the model under test, and records model outputs for analysis

4 File Type and Declaration Files are distinguished by the type of information stored type textFileType is file of string ; type integerFileType is file of integer ; File declarations VHDL 1987 file infile: textFileType is in “inputdata.txt”; file outfile: textFileType is out “outputdata.txt”; File declarations VHDL 1993 file infile: textFileType open read_mode is “inputdata.txt”; file outfile: textFileType open write_mode is “outputdata.txt”;

5 Binary File I/O (VHDL 1987) VHDL 1987 provides read(f,value), write(f, value) and endfile(f) It uses implicit file open operations via file declarations test of binary file I/O -- entity io87 is end io87; architecture beh of io87 is begin process type IntegerFileType is file of integer; file dataout:IntegerFileType is out “output.txt”; variable check :integer :=0; begin for count in 1 to 10 loop check := check+1; write(dataout, check); end loop; wait; end process; end beh;

6 Binary File I/O (VHDL 1993) – cont. entity io93 is end entity io93; architecture beh of io93 is begin process is type IntFileType is file of integer; -- file declarations file dataout :IntFileType; variable count : integer:= 0; variable fstatus: FILE_OPEN_STATUS; begin file_open(fstatus,dataout,"myfile.txt",write_mode); -- open the file for j in 1 to 8 loop write(dataout,count); -- some random values count := count+2; end loop; wait; -- an artificial way to stop the process end process; end architecture beh;

7 VHDL ’93 provides READ(file_handle,value), WRITE(file_handle, value) and ENDFILE(file_handle), and also FILE_OPEN() and FILE_CLOSE() VHDL ’93 allows both explicit and implicit file open operations procedure FILE_OPEN( file file_handle: FILE_TYPE File_name: in STRING; Open_kind: in FILE_OPEN_KIND := READ_MODE); procedure FILE_OPEN(File_Status:out FILE_OPEN_STATUS; file file_handle: FILE_TYPE File_name: in STRING; Open_kind: in FILE_OPEN_KIND := READ_MODE); procedure FILE_CLOSE( file file_handle: FILE_TYPE) Binary File I/O (VHDL 1993) – cont.

8 FILE_OPEN_KIND may have one of 3 values: READ_MODE, WRITE_MODE, APPEND_MODE FILE_STATUS may have one of 4 values: OPEN_OK file open operation was successfull STATUS_ERROR attempted to open an already open file NAME_ERROR file not found MODE_ERROR file cannot be opened in this mode Binary File I/O (VHDL 1993)

9 Binary File I/O limitations The values passed on each line of the file are all of the same type It would be very “handy” to be able to pass different types ……..

10 The TEXTIO Package line file read(buf,c) write(buf,arg) writeline() buffer One common approach to I/O for the predefined types of the language is to use the TEXTIO package I/O is text based (ASCII) The TEXTIO package is in the STD library, which is implicitly declared. You do not need to declare the usage of the library STD, however you still need to declare the use of the package contents via the use clause

11 The TEXTIO Package Text based I/O A file is organized by lines read() and write() procedures operate on line data structures readline() and writeline() procedures transfer data from-to files The TEXTIO package is in the library STD and provides: procedures for reading and writing the pre-defined types from lines predefined access to std_input and std_output procedures names are overloaded procedure

12 Example: Use of the TEXTIO Package use std.textio.all; entity formatted_io is -- this entity is empty end formatted_io; architecture behavioral of formatted_io is begin process is file outfile :text; -- declare the file to be a text file variable fstatus :File_open_status; variable count: integer := 5; variable value : bit_vector(3 downto 0):= X”6”; variable buf: line; -- buffer to file begin -- open the file for writing file_open(fstatus, outfile,”myfile.txt”, write_mode); L1: write(buf, “This is an example of formatted I/O”); L2: writeline(outfile, buf); -- write buffer to file L3: write(buf, “The First Parameter is =”); L4: write(buf, count); L5: write(buf, ‘ ‘); L6: write(buf, “The Second Parameter is = “); L7: write(buf, value); L8: writeline(outfile, buf); L9: write(buf, “...and so on”); L10: writeline(outfile, buf); L11: file_close(outfile); -- flush the buffer to the file wait; end process; end architecture behavioral; This is an example of formatted I/O The First Parameter is = 5 The Second Parameter is = and so on Result

13 Passing Filenames interactively process is variable buf : line; variable fname : string(1 to 10); begin prompt and read filename from standard input -- write(output, “Enter Filename: “); readline(input, buf); read(buf, fname); process code -- end process; Generally “input” and “output” are mapped to standard input and standard output respectively

14 Extending TEXTIO for other Datatypes Hide the ASCII format of TEXTIO from the user Create type conversion procedures for reading and writing desired datatypes Encapsulate procedures in a package Install package in a library and make its contents visible via the use clause library ieee; use ieee.std_logic_textio.all;

15 Constructing Testbenches General approach: Apply stimulus vectors and Measure and Record response vectors If the number of test vectors is too big procedural vectors generation is preferable to FILE I/O vectors generation Clock and reset generation is usually done with procedural stimulus

16 Testbenches: I/O stimulus generation example... while not endfile(vectors) loop readline(vectors, vectorline); -- file format is if (vectorline(1) = ‘#’ then next; end if; read(vectorline, datavar); read((vectorline, A); -- A, B, and C are two bit vectors read((vectorline, B); -- of type std_logic read((vectorline, C); -- --signal assignments Indata <= to_stdlogic(datavar); A_in <= unsigned(to_stdlogicvector(A)); -- A_in, B_in and C_in are B_in <= unsigned(to_stdlogicvector(B)); -- of unsigned vectors C_in <= unsigned(to_stdlogicvector(C)); wait for ClockPeriod; end loop;...

17 Testbenches: Validation Compare reference vectors with response vectors and record errors in external files In addition to failed tests record simulation time

18 The “ASSERT” Statement Designer can report errors at predefined levels: NOTE, WARNING, ERROR and FAILURE (enumerated type) Report argument is a character string written to simulation output TEXTIO may be faster than ASSERT if we do not need to stop the simulation assert Q = check(1) and Qbar = check(0) report “Test Vector Failed” severity error;

19 Summary Basic Input/Output Binary I/O ASCII I/O and the TEXTIO package VHDL 87 vs. VHDL 93 Testbenches The ASSERT statement