Reading and writing files from Verilog model.pdf

Reading and writing files from Verilog models

http://larc.ee.nthu.edu.tw/~lmdenq/doc/fileio.htm

Introduction

This describes how you can read and write files in a Verilog model using a set of user functions,

based on the C stdio package. With these functions you can perform file input and output directly

in Verilog models without having to learn C or the PLI. This code works with VCS, MTI, Verilog-XL,

and NC-Verilog (see $fread for one restriction).

Note that Synopsys' VCS 6.1, NC-Verilog 3.3, and MTI's ModelSim 5.5 offer native support for the

IEEE-1364 2001 standard. Verilog-XL does not support these tasks except through this PLI

Restrictions and Caveats

Reading pattern files

Comparing outputs with expected results

Reading script files

Reading data files into memories

Linking with VCS

Linking with Verilog-XL

Linking with MTI

Linking with NC-Verilog

This program is free software; you can redistribute it and/or modify it under the terms of the

GNU General Public License as published by the Free Software Foundation; either version 2 of the

License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;

without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR

PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if

not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

files to load memories, apply stimulus, and control simulation. Files can also be written. The

format of the file I/O functions is based on the C stdio routines, such as fopen, fgetc, fprintf, and

fscanf.

The Verilog language has a rich set of system functions to write files ($fdisplay, $fwrite, etc.) but

only reads files with a single, fixed format ($readmem). In the past if you wanted to read a file

that was not in $readmem format, you would have to learn the Programming Language Interface

(PLI) and the C language, write C code to read the file and pass values into Verilog, then debug

the combined C and Verilog code. In addition, the Verilog is limited to 32 open files at a time.

However, using the new file I/O system functions you can perform your file I/O directly from

have hundreds of log files open simultaneously (though they are written to one at a time)

Code for all the examples in this file is included in the examples directory for the file I/O

Note that these system tasks behave the same as the equivalent stdio routines. For example,

$fscanf will skip over white-space, including blank lines, just like fscanf(). You can prototype code

in C then convert it to Verilog.

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Differences between fileio and IEEE-1364

Verilog-2001 (V2K) standard

In V2K, there is a single $fopen for both multi-channel descriptors (MCD) and file descriptors (FD).

Whether an FD or MCD is produced is indicated by the presence of a mode string added to

$fopen in V2K:

file = $fopen("filename", "w"); // FD

file = $fopen("filename"); // MCD

Fileio supports the V2K $fopen format under a package compilation switch but that then blocks

any use of MCDs since it hides the builtin $fopen.

Fileio supports the V2K $fclose format under a package compilation switch but that then blocks

any use of MCDs since it hides the builtin $fclose.

3) Fileio $getchar is not directly supported in Verilog-2001. The operation can be done by using

$fgetc('h8000_0000) which makes use of the reserved FD for stdin.

4) Fileio defines $fgets as:

r = $fgets(string, n, file);

5) Fileio $scanf is not directly supported in Verilog 2001. The operation can be done by using:

$fscanf('h8000_0000, format, args);

which makes use of the reserved FD for stdin.

6) Fileio does not support ? as an alias for X; V2K does.

9) Fileio does not support %u, %z, %v, %t, or %m input format specifiers; V2K supports all of

them.

10) Fileio supports special character input handling for \ (i.e. \\, \oNNN); V2K does not support

this (not in LRM).

11) Fileio requires that $fread on a memory use "mem[0]" as the memory referend. V2K

requires "mem" since "mem[0]" will be taken as a register read.

produce the same result independent of whether the target is a string, file, or standard output.

13) Fileio $ferror only returns a status. V2k $ferror takes a second parameter and stores the

error string in that register. Additionally, V2K $ferror accepts a file descriptor with the value 0

and simple produces the most recent system error status.

14) Fileio requires an argument to $fflush; V2K permits a parameterless call and flushes all files

(including MCD files) in that case. V2K $fflush supports either MCDs or FDs.

15) V2K supports $rewind which Fileio does not.