Netlist.pm

#** @file Netlist.pm
# @verbatim
#-------------------------------------------------------------------------------
#  University of Applied Sciences Technikum Wien
#
#  Department of Embedded Systems
#  http://embsys.technikum-wien.at
#
#  Josef Ressel Center for Verification of Embedded Computing Systems
#  http://vecs.technikum-wien.at
#
#-------------------------------------------------------------------------------
#  File:              Netlist.pm
#  Created on:        29.04.2015
#  $LastChangedBy$
#  $LastChangedDate$
#
#  Description:
#
#  FIJI Netlist class: Functions to instrument & export a Verilog::Netlist
#-------------------------------------------------------------------------------
# @endverbatim
#*

## @file Netlist.pm
# @brief Contains class \ref FIJI::Netlist

## @class FIJI::Netlist
# @brief Functions to instrument & export a Verilog::Netlist
package FIJI::Netlist;

use strict;
use warnings;

use Scalar::Util 'blessed';
use Log::Log4perl qw(get_logger :easy);
use File::Basename qw(basename);

use Verilog::Netlist 99.415;
use Verilog::Language 99.415;
use Data::Dumper;

use FIJI::VHDL;

use constant HIERSEP               => "|";
use constant FIJI_NAMESPACE_PREFIX      => "fiji_";
use constant FIJI_PORT_IN_POSTFIX  => "_inj_i";
use constant FIJI_PORT_OUT_POSTFIX => "_ori_o";
use constant MAX_UNIQUE_TRIES => 10;

use constant FIJI_LOGO => <<logo_end;
//  FIJIFIJIFIJIFIJIFIJIFIJIFIJIFIJIFIJIFIJI
//  FIJIFIJIFIJIFIJIF   FIJIFIJIFIJIFIJIFIJI
//  FIJIFIJIFIJIFIJ    IFIJIFIJIFIJIFIJIFIJI
//  FIJIF       FI           IJIFIJIFIJIFIJI
//  FIJIFIJIFI            JIFIJIFIJIFIJIFIJI
//  FIJIFIJI            FIJIFIJIFIJIFIJIFIJI
//  FIJIFI    JI   IFI   IJIFIJIFIJIFIJIFIJI
//  FIJIF   FIJ   JIFIJ   JIFIJIFIJIFIJIFIJI
//  FIJIFIJIFI   IJIFIJI   IFIJIFIJIFIJIFIJI
//  FIJIFIJIF    IJIFIJIFIJIFIJIFIJIFIJIFIJI
//  FIJIFIJI    FIJIFIJIFIJIFIJIFIJIFIJIFIJI
//  FIJIFIJ     FIJIF           FIJIFIJIFIJI
//  FIJIFI     IFI      Fault      IFIJIFIJI
//  FIJIF             InJection     FIJIFIJI
//  FIJ              Instrumenter    IJIFIJI
//  F                                    IJI
//  FIJIFIJIFIJIFIJIFIJIFIJIFIJIFIJIFIJIFIJI
logo_end

## @function public new ()
# @brief creates a new FIJI::Netlist object
#
# @returns the newly created FIJI::Netlist object
sub new {

    my ($class) = @_;

    my $self = {};
    bless $self, $class;

    $self->{'nl'} = new Verilog::Netlist(

        # options => $opt,
        # keep_comments => 1, # include comments in netlist
        link_read_nonfatal => 1,    # do not fail if module description not found
        use_vars           => 1,
    );
    return $self;
}

## @method public read_file ($filename)
# @brief Tries to read a Verilog netlist from the given file
#
# @param filename    The Verilog file to read
#
# @returns 1   if an error occurred
# @returns 0   if successful
sub read_file {
    my $logger = get_logger("");
    my ($self, $filename) = @_;

    ## Netlist synthesized from VHDL could contain SV keywords at this point.
    Verilog::Language::language_standard("1364-2001");

    $logger->info("Reading in netlist from file \"$filename\".");
    eval {
        $self->{'nl'}->read_file(filename => $filename);    # read Verilog file
        $self->{'nl'}->link();                              # Read in any sub-modules
    };

    if ($self->{'nl'}->errors() != 0 || $@) {
        $logger->error("Could not parse $filename!", $@ ? "\n" . $@ : "");
        return 1;
    }

    $self->{'filename'} = $filename;

    $logger->info("Successfully read in netlist from file \"$filename\".");
    return 0;
}

## @method public get_toplevel_port_names ()
# @brief retrieves the port names of all toplevel modules
#
# @returns an array of Verilog::Port references
sub get_toplevel_port_names {
    my ($self, $dir) = @_;
    my $ports_ref = [];
    foreach my $mod ($self->{'nl'}->top_modules_sorted) {
        foreach my $port ($mod->ports) {
            if (   !defined($dir)
                || ($dir eq "o" && $port->direction eq "out")
                || ($dir eq "i" && $port->direction eq "in"))
            {
                push @{$ports_ref}, $port->name;
            }
        }
    }
    return $ports_ref;
}

## @method public get_toplevel_module ()
# @brief retrieves the port names of all toplevel modules
#
# @returns a Verilog::Module reference
sub get_toplevel_module {
    my ($self) = @_;
    my @m      = $self->{'nl'}->top_modules_sorted;
    my $n      = @m;
    return $m[0] if ($n == 1);
    return "More than one toplevel module present in netlist." if ($n > 1);
    return "No toplevel module found.";
}

## @method public get_nets ()
# @brief retrieves all nets in the netlist
#
# @returns an array of hashes for all nets containing:
# 'name' the name of the net
# 'path' the hierarchical path of the net
# 'net'  the Verilog::Netlist::Net reference to the net
sub get_nets {
    my ($self) = @_;

    # my $nets_ref = {'metadata' => [], 'names' => [], 'nets' => []};
    my $nets_ref = [];
    my $hier     = "";
    foreach my $mod ($self->{'nl'}->top_modules_sorted) {
        $self->_get_subnets($nets_ref, $mod, $hier);
    }
    return $nets_ref;
}

sub _extract_low_high {
    my ($in_low, $in_high) = @_;
    my ($out_low, $out_high);

    # msb might be lower than lsb if index range is "upto" -> swap
    if ($in_high < $in_low) {
        $out_low = $in_high;
        $out_high = $in_low;
    } else {
        $out_low = $in_low;
        $out_high = $in_high;
    }
    return ($out_low, $out_high);
}

#** @method private _get_subnets ($nets_ref,$mod,$hier)
# @brief retrieves all nets in the given module
#
# @param nets_ref    the central reference to push found nets (name,path,netref) to
# @param mod         the module to search
# @param hier        a string representing the current hierarchy level, separated
#                    be HIERSEP
sub _get_subnets {

    my $logger = get_logger("");
    my ($self, $nets_ref, $mod, $hier) = @_;

    my $thishier = $hier;
    $thishier .= HIERSEP if $thishier ne "";
    $thishier .= $mod->name;

    foreach my $n ($mod->nets) {
        if (defined($n->msb) && defined($n->lsb)) {
            my ($low, $high) = _extract_low_high($n->lsb, $n->msb);
            for (my $sub = $low ; $sub <= $high ; $sub++) {
                my $thisnet_ref = {name => $n->name . "[$sub]", path => $thishier, net => $n, index => $sub};
                push(@{$nets_ref}, $thisnet_ref);
            }
        } else {
            my $thisnet_ref = {name => $n->name, path => $thishier, net => $n};
            push(@{$nets_ref}, $thisnet_ref);
        }

    }

    foreach my $cell ($mod->cells) {
        if (defined($cell->submod)) {
            $self->_get_subnets($nets_ref, $cell->submod, $thishier);
        }
    }
}

## @function private _check_name_in_hierarchy ($startmod,$name)
# @brief checks if a given name exists
# checks if the $name exists as port, net, or cell name in the instantiation tree.
#
# @param startmod    the module to start with
# @param name        the name to check against
sub _check_name_in_hierarchy {

    my $logger = get_logger("");
    my ($startmod, $name) = @_;
    my $nl = $startmod->netlist;

    $logger->debug("Checking \"" . $startmod->name . "\" for name \"$name\"");

    # check if a net is named the same
    for my $net ($startmod->nets) {
        if ($net->name eq $name) {
            my $msg = "Name \"$name\" does already exist as net in " . $startmod->name;
            return $msg;
        }
    }

    # check if a port is named the same
    for my $port ($startmod->ports) {
        if ($port->name eq $name) {
            my $msg = "Name \"$name\" does already exist as port in " . $startmod->name;
            return $msg;
        }
    }

    for my $cell ($startmod->cells) {
        if ($cell->name eq $name) {
            my $msg = "Name \"$name\" does already exist as cell in " . $startmod->name;
            return $msg;
        }
    }

    # find any module instantiating the current start module
    foreach my $mod ($nl->modules) {
        foreach my $cell ($mod->cells) {
            if (defined $cell->submod && $cell->submod == $startmod) {
                my $msg = _check_name_in_hierarchy($mod, $name);
                return $msg if defined $msg;
            }
        }
    }

    return undef;
}

## @function private _add_port_to_hierarchy ($startmod,$name,$function,$index,$indent)
# @brief adds a port to all modules starting from a leaf node
#
# @param startmod    the module to start with
# @param name        the port name to be generated
# @param function    the function of this port in FIJI (FIJI::VHDL->FIJI_PORTTYPE_xxx)
# @param index       for ORIGINAL,MODIFIED and FAULT_DETECT: the index of this net
# @param indent      optional, needed just for formatting logging output
#
# @returns undef if the given port $name is already found
# @returns Verilog::Port reference to the new port if successful
sub _add_port_to_hierarchy {

    my $logger = get_logger("");
    my ($startmod, $name, $function, $index, $indent) = @_;
    my $nl        = $startmod->netlist;
    my $direction = "undef";
    if (!defined $indent) {
        $indent = "";
    } else {
        $indent .= "  ";
    }

    return undef if ($startmod->find_port($name));

    $logger->debug($indent . "Adding port \"$name\" to module \"" . $startmod->name . "\"");

    # decide direction
    if (   $function == FIJI::VHDL->FIJI_PORTTYPE_MODIFIED
        || $function == FIJI::VHDL->FIJI_PORTTYPE_RESET_TO_DUT)
    {
        $direction = "in";
    } else {
        $direction = "out";
    }

    # generate port
    my $np = $startmod->new_port(name => $name, direction => $direction);

    # set port type for wrapper generation
    $np->userdata(FIJI::VHDL->FIJI_USERDATA_PORTTYPE, $function);

    # set indices
    if (   $function == FIJI::VHDL->FIJI_PORTTYPE_MODIFIED
        || $function == FIJI::VHDL->FIJI_PORTTYPE_ORIGINAL)
    {
        $np->userdata(FIJI::VHDL->FIJI_USERDATA_FIU_INDEX, $index);
    } elsif ($function == FIJI::VHDL->FIJI_PORTTYPE_FAULT_DETECTION) {
        $np->userdata(FIJI::VHDL->FIJI_USERDATA_FD_INDEX, $index);
    }

    # let Verilog-Perl create a new net for the new port.
    $startmod->link;

    # find all modules instantiating the current module
    foreach my $mod ($nl->modules_sorted) {
        foreach my $cell ($mod->cells) {
            if (defined $cell->submod && $cell->submod == $startmod) {
                $logger->debug($indent . "Adding pin \"$name\" to cell \"" . $cell->name . "\"");
                $logger->debug($indent . "Connecting pin \"" . $cell->name . HIERSEP . $name . "\" to port \"" . $np->module->name . HIERSEP . $np->name . "\"");
                $cell->new_pin(
                    name     => $name,
                    portname => $np->name,
                    netnames => [{'netname' => $np->net->name}],
                );

                # let verilog-perl find the net and port.
                # @FIXME sufficient to link "mod" here?
                $mod->link;
                _add_port_to_hierarchy($mod, $name, $function, $index, $indent);
            }
        }
    }

    return $np;
}

## @method public net_add_function($net, $function, $port_name, $index)
# @brief Generate external access to a single net
#
# Performs the following steps:
#    1.  check if the default port name does not yet exist
#    1a. if it exists, generate a new net name
#    2.  add a port through the entire hierarchy
#    3.  assign the net to the port using a contassign statement
#
# @param net         the Verilog::Net object to be used
# @param function    the function out of FIJI::VHDL->FIJI_PORTTYPE_xxx
# @param port_name   how the port shall be named (will be prefixed with "fiji_")
# @param index       for some FIJI_PORTTYPEs, an index is needed (FIU and Fault Detect)
#
# @returns undef
sub net_add_function {
    my $logger = get_logger("");
    my ($self, $net, $function, $port_name, $index) = @_;

    $logger->debug("Adding function to \"" . $net->module->name . "\", net \"" . $net->name . "\"");

    my $prefix = "fiji_";

    my $unique_name = _unique_name($net->module,$prefix.$port_name);

    if (!defined $unique_name) {
        $logger->error("Could not find a unique name for prefix ".$prefix.$port_name)
    }

    $logger->debug("\"" . $unique_name . "\" can be used as fiji connector");
    my $op = _add_port_to_hierarchy($net->module, $unique_name, $function, $index);

    $logger->debug("Connecting Port \"" . $op->name . "\" to net \"" . $net->name . "\"");

    # connect the net to the newly created port
    $net->module->new_contassign(
        keyword => "assign",
        lhs     => $op->name,
        rhs     => $net->name,
        module  => $op->module,
        netlist => $op->module->netlist
    );

    return undef;
}

# tries to generate a unique but recognizable net name by appending a
# random hex number if necessary
sub _unique_name {
    my $logger = get_logger("");
    my ($mod,$requested_name) = @_;

    # check if requested name is OK
    my $msg = _check_name_in_hierarchy($mod, $requested_name);
    
    if (!defined $msg) {
        return $requested_name;
    }

    # else try up to 10 times to generate a unique name by appending
    # a 4-digit random hex number
    for (my $tries = 0; $tries < MAX_UNIQUE_TRIES; $tries++) {
        my $name = sprintf("%s_%04x", $requested_name, rand(0xffff));
        $msg = _check_name_in_hierarchy($mod, $name);
        return $name if (!defined $msg);
    }
    
    return undef
}

# take a possible escaped identifier and make it a legal _and_ sane verilog identifier
sub _sanitize_identifier {
    my $insane = shift;

    # Verilog allows "non-alphanumeric" characters in identifiers if they start with a backslash and end with whitespace (escaped identifiers) but we don't want to.
    my $sane = ($insane =~ s/[^a-zA-Z0-9_]+/_/gr);
    # VHDL signals must not contain multiple subsequent underscores
    $sane =~ s/__+/_/g;
    return $sane
}

sub generate_contassign {
    my $logger = get_logger("");
    my ($module, $lhs, $rhs) = @_;
    $logger->trace("Setting \"$lhs = $rhs\"");
    $module->new_contassign(
        keyword => "assign",
        lhs     => $lhs,
        rhs     => $rhs,
        module  => $module,
        netlist => $module->netlist
    );
}

## @method public instrument_net($net,$fiu_idx, $driver, $driver_type)
# @brief instruments a single net for fault injection
#
# This method performs the following steps
#   1. determine the connected objects (driver as well as driven nets, pins etc)
#   2. generate external access output and input ports and intermediate nets
#   3. interconnect these ports to the matching driver and driven cells via the intermediate nets
#
# @param net_path        the Verilog::Net to instrument
# @param fiu_idx         the FIU number this external access shall be connected to
# @param driver_path     the path to the driver of this net (optional but depends on driver_type)
# @param driver_type     the type of the driver (can be PIN, PORT, ASSIGN) (optional but depends on driver_path)
#
# @returns STRING          if an error occurred
# @returns undef           if successful
sub instrument_net {

    my $logger = get_logger("");
    my ($self, $net_path, $fiu_idx, $driver_path, $driver_type) = @_;

    # split hierarchical net path
    my $net_descriptor = $self->get_netdescriptor_from_path($net_path);

    if (ref($net_descriptor) ne "HASH") {
        return $net_descriptor;
    }

    my $net = $net_descriptor->{'net'};
    my $net_name = $net_descriptor->{'net_name'};
    my $msb = $net_descriptor->{'msb'};
    my $lsb = $net_descriptor->{'lsb'};
    my $mod = $net_descriptor->{'mod'};
    my $idx = '';
    my $idx_postfix = '';

    # We need to produce names for the i/o ports that route the signals
    # to the FIC. To allow to instrument multiple indices of a single
    # signal we need to make these names unique thus we even include the
    # indices if used.
    if (defined $msb && defined $lsb) {
        if ($msb ne $lsb) {
            # We dont support the instrumentation of vectors (only sinlge indices of busses).
            return "The given net to instrument is a vector with multiple bits.\nThis is not supported.\nMay you want to instrument a single bit of said vector instead?";
            # $idx         = "[".$msb.":".$lsb."]";
            # $idx_postfix = "_".$msb."_".$lsb."_";
        } else {
            $idx         = "[".$msb."]";
            $idx_postfix = "_".$msb."_";
        }
    }

    $logger->info("Instrumenting \"" . $net->module->name . "\", net \"" . $net->name.$idx . "\"");

    # we want to perceive the connection state before any changes (at least w/o changes by this invocation)
    my %connections;
    my $rv = $self->_get_net_connections($net, \%connections, $msb, $driver_path, $driver_type);
    return $rv if (defined $rv);

    my $output_name = (FIJI_NAMESPACE_PREFIX . $net->name . $idx_postfix . FIJI_PORT_OUT_POSTFIX);
    $output_name = _sanitize_identifier($output_name);
    my $input_name  = (FIJI_NAMESPACE_PREFIX . $net->name . $idx_postfix . FIJI_PORT_IN_POSTFIX);
    $input_name = _sanitize_identifier($input_name);

    # generate unique name for output port, return with error message if that fails
    my $unique_output_name = _unique_name($mod, $output_name);
    return "Could not generate unique name for prefix $output_name" if (!defined $unique_output_name);

    $logger->debug("\"" . $unique_output_name . "\" will be used as fiji connector (output)");
    my $op = _add_port_to_hierarchy($mod, $unique_output_name, FIJI::VHDL->FIJI_PORTTYPE_ORIGINAL, $fiu_idx);

    # generate unique name for input port, return with error message if that fails
    my $unique_input_name = _unique_name($mod, $input_name);
    return "Could not generate unique name for prefix $input_name" if (!defined $unique_input_name);

    $logger->debug("\"" . $unique_input_name . "\" will be used as fiji connector (input)");
    my $ip = _add_port_to_hierarchy($mod, $unique_input_name, FIJI::VHDL->FIJI_PORTTYPE_MODIFIED, $fiu_idx);


    # Add an intermediate net to allow patching without rewriting connections everywhere
    #
    # We use the requested signal as sink/destination.
    # That way we only need to change the driver to drive our intermediate net.
    #
    # We first generate a suitable name for the intermediate net,
    # then change the driver accordingly and handle other aspects of
    # the intermediate net at the very bottom of this function.

    # Choose intermediate net name
    my $net_name_tmp = _sanitize_identifier(FIJI_NAMESPACE_PREFIX . $net_name . "_in_tmp");
    my $name_check = _check_name_in_hierarchy($mod, $net_name_tmp);

    # Switch the driver from the original signal to the intermediate net.
    my $driver_is_vector = 0;
    my $driver_is_port = 0;
    foreach my $connection (@{$connections{'drivers'}}) {
        if (ref($connection) eq "Verilog::Netlist::Pin") {
            # If the driver is a pin of a (sub)cell, connect this pin to the intermediate net
            $logger->debug("Connecting (output) pin \"" . $connection->cell->name . HIERSEP . $connection->name . "\" to intermediate net \"$net_name_tmp\"");
            # FIXME: do concatenations really work? They are apparently split already by Verilog::perl but...
            for my $netname (@{$connection->netnames}) {
                if ($netname->{'netname'} eq $net->name) {
                    $netname->{'netname'} = $net_name_tmp; # FIXME: do we need to force a re-link (by deleting $connection->nets)?
                    # This net is a vector if the underlying net is a bus and we do not just select a single bit
                    if (defined($net->msb) || (!defined($netname->{'msb'}) || $netname->{'msb'} != $netname->{'lsb'})) {
                        $driver_is_vector = 1;
                    }
                }
            }
            # $connection->port(undef);    # resolved by link
        } else {
            if (ref($connection) eq "Verilog::Netlist::Port") {
                $driver_is_port = 1;
                # If instrumented net is a vector we will need an intermediate bus
                if (defined($net->msb)) {
                    $driver_is_vector = 1;
                    # If port is vector change type of existing non-instrumented input to wire -
                    # practically transforming it to an ordinary wire that can easily be intrumented
                    $connection->net->net_type("wire");
                    $connection->net->port(undef);
                    $logger->debug("Transforming previous port named \"". $connection->name . "\" into an ordinary wire");
                }
                # FIXME: rename port in instantiation of current module
                $logger->warn("Instantiation of module \"" . $mod->name . "\" needs to change port \"" . $connection->name . "\" to \"$net_name_tmp\" - not supported yet...");
                # if ($mod->is_top) {
                    # FIXME: add naming information for wrapper generator
                # } else {
                # }
                # Eventually connect this port to the intermediate net by changing its name
                $logger->debug("Connecting (input) port \"" . $connection->name . "\" to intermediate net \"$net_name_tmp\"");
                $connection->name($net_name_tmp);
            } elsif (ref($connection) eq "Verilog::Netlist::ContAssign") {
                # FIXME: concatenations
                # If the driver is an assignment, replace the LHS with the intermediate net
                if(0) {
                    $logger->debug("Connecting to intermediate net \"" . $net_name_tmp . "\" the continuous assignment of \"" . $connection->rhs . "\"");
                    $connection->lhs($net_name_tmp);
                } else {
                    # Retrieve net object of LHS of the assignment to determine if it is a bus and if the assignment is to the complete net or a single bit.
                    my $lhs_elems = $self->_extract_netstring_elements($connection->lhs);
                    my $lhs_net_name = $lhs_elems->{'net_name'};
                    my $lhs_net = $mod->find_net($lhs_net_name);
                    if (!defined($lhs_net)) {
                        my $lhs_port = $mod->find_port($lhs_net_name);
                        if (!defined($lhs_port)) {
                            return "Could not find net or port in module \"" . $mod->name . "\" matching LHS of assignment \"" . $connection->lhs . "\" = \"" . $connection->rhs . "\"";
                        }
                        # FIXME: so this is actually a port...
                        $logger->fatal("Found port name in continuous assignment. This is not supported yet.");
                        return "BORKED";
                    }
                    my $rhs_elems = $self->_extract_netstring_elements($connection->rhs);
                    my $rhs_net_name = $rhs_elems->{'net_name'};

                    my $rhs_net = $mod->find_net($rhs_net_name);
                    # If driver is a vector we need a vectored intermediate bus.
                    # This is the case if on the RHS
                    #   - the underlying net is a vector and there are no indices
                    #   - the underlying net is a vector and there are two different indices
                    if (defined($rhs_net->msb) && (!defined($rhs_elems->{'msb'}) || ($rhs_elems->{'msb'} != $rhs_elems->{'msb'}))) {
                        $driver_is_vector = 1;
                    }
                    $logger->debug("Connecting to intermediate net \"" . $net_name_tmp . "\" the continuous assignment of \"" . $connection->rhs . "\"");
                    $connection->lhs($net_name_tmp);
                     if(1) {} else {
                        # If LHS is a bus however we need to drive the bit we want to instrument only
                        $logger->debug("Connecting to intermediate net \"" . $net_name_tmp."[".$msb."]" . "\" the continuous assignment of \"" . $connection->rhs . "\"");
                        $connection->lhs($net_name_tmp."[".$msb."]");
                        # $logger->debug("Connecting to non-instrumented bits of the intermediate net \"" . $connection->lhs."[".$msb."]" . "\" the continuous assignment of \"" . $net_name_tmp."[".$msb."]" . "\"");
                        # generate_contassign($mod, $connection->lhs."[".$msb."]", $net_name_tmp."[".$msb."]");
                    }
                }
            } else {
                $logger->debug("Driver instance is neither pin, port nor contassign?");
            }
        }
    }

    # Below we create the intermediate net as needed.
    # A suitable name for the tmp net was already determined.
    # 1.) Generate the tmp net.
    # 2.) Assign injected signal from input pin to original signal.
    # 3.) If original signal is a bus forward orignal data from tmp net to untouched bits of original signal
    # 4.) Forward (injected bit of) intermediate net to FIC by assigning it to the output pin
    #
    my $net_tmp;
    # If the name is already taken then assume we need to instrument another bit of a bus
    # FIXME: maybe we should try harder to find out the reason why _check_name_in_hierarchy failed
    if (defined($name_check)) {
        if (!defined($net->msb)) {
            my $err = "Tried to instrument non-vector signal (\"$net_name\") twice or we really have a naming conflict.";
            $logger->error($err);
            return $err;
        }
        $net_tmp = $mod->find_net($net_name_tmp);
        # We need to undo the previous assignment of the respective bit
        foreach my $statement ($mod->statements) {
            if ($statement->rhs =~ /^[ \t]*~?[ \t]*\Q$net_name_tmp\E(\[(\Q$msb\E)\])?$/) {
                $logger->debug("    unassigning \"" . $statement->lhs . " = " . $statement->rhs . "\"");
                $statement->delete();
            }
        }

        $logger->debug("    reassigning \"" . $net_name."[".$msb."] = " . $ip->net->name . "\"");
        generate_contassign($mod, $net_name."[".$msb."]", $ip->net->name);
    } else {
        # 2.) Generate intermediate (tmp) net for easier input and output routing
        # If the driver is a vector then we will generate a vectored intermediate net as well.
        # However, if the driver is a single-bit net or a single bit of a vector we get away
        # without an intermediate net.
        my @net_cfg = (name => $net_name_tmp);
        push(@net_cfg, net_type => 'input') if $driver_is_port;
        
        if ($driver_is_vector) {
            $logger->debug("Generating intermediate " . ($driver_is_port ? 'port' : 'wire') . " named \"" . $net_name_tmp . "[" . $net->msb .":". $net->lsb . "]\" to patch \"$net_name\"");
            push(@net_cfg,
                msb => $net->msb,
                lsb => $net->lsb,
            );
        } else {
            $logger->debug("Generating intermediate " . ($driver_is_port ? 'port' : 'wire') . " named \"" . $net_name_tmp . "\" to patch \"$net_name\"");
        }
        $net_tmp = $mod->new_net(@net_cfg,);

        # 3+4.) Assign injected (and uninjected bits of vectors) to previous signal.
        # Below we assign the altered signal from the FIC to the original signal.
        # For busses we need to connect all non-instrumented bits of the tmp net
        # additionally to preserve their unmodified values.

        if (!defined($net->msb)) {
            # If the instrumented net is not a vector we simply assign the injected signal
            generate_contassign($mod, $net_name, $ip->net->name);
        
        } elsif (!defined($net_tmp->msb)) {
            # If the net is a vector but the driver was driving only one bit
            # then we need to drive the originally driven bit only
            generate_contassign($mod, $net_name."[".$msb."]", $ip->net->name);
        } else {
            # For drivers of complete busses we need to connect all non-instrumented bits of the tmp net
            # additionally to preserve their unmodified values.
            my ($low, $high) = _extract_low_high($net_tmp->lsb, $net_tmp->msb);
            for (my $i = $low ; $i <= $high ; $i++) {
                if ($i == $msb) {
                    generate_contassign($mod, $net_name."[".$i."]", $ip->net->name);
                } else {
                    generate_contassign($mod, $net_name."[".$i."]", $net_name_tmp."[".$i."]");
                }
            }
        }
    }

    # 5.) Connect the tmp net to the output pin that forwards the signal to the FIC
    if (!defined($net_tmp->msb)) {
        $logger->debug("    assigning \"" . $op->net->name . " = " . $net_name_tmp . "\"");
        generate_contassign($mod, $op->net->name, $net_name_tmp);
    } else {
        $logger->debug("    assigning \"" . $op->net->name . " = " . $net_name_tmp ."[".$msb."]\"");
        generate_contassign($mod, $op->net->name, $net_name_tmp."[".$msb."]");
    }
    $mod->link;
    return undef;
}

## @method public validate_driver($net_path, $driver_path, $driver_type)
# @brief Check if the given driver is valid for the given net
#
# Check if the driver specified by $driver_type and $driver_path
# is actually connected to the net specified by $net_path
#
# @param net_path        The hierarchical path of the net, separeted by HIERSEP
# @param driver_path     The hierarchical path of the driver object, separated by HIERSEP
# @param driver_type     The type of the driver object, one of {PIN, PORT, ASSIGN}
#
# @returns STRING          if an error occurred
# @returns undef           if successfull
sub _validate_driver {
    my $logger = get_logger("");
    my ($self, $net_path, $driver_path, $driver_type) = @_;

    my $connection_object = $self->get_connection_object($driver_path, $driver_type);
    my $connections       = {};
    $self->_get_net_connections_from_path($net_path, $connections);

    goto FAIL if (!defined $connection_object);

    my @in_drivers     = grep { $_ == $connection_object } @{$connections->{'drivers'}};
    my @in_connections = grep { $_ == $connection_object } @{$connections->{'connected'}};

    goto FAIL if (@in_drivers == 0 && @in_connections == 0);

    return undef;

FAIL:
    my $msg = "No possible driver found";
    $logger->error($msg);
    return $msg;
}

## @function private _select_driver($connected,$net)
# @brief Prompt the user to select a driver for a net from a set of given cells/outputs
#
# @param connected       list reference containing connected Verilog::Perl instances
# @param net             the Verilog::Perl::Net instance to select the driver for
#
# @returns STRING          if an error occurred
# @returns Driver object   if successful
sub _select_driver {
    my ($connected, $net) = @_;

    print "Select driver for net " . $net->name . ": \n";
    my $di;
    for ($di = 0 ; $di < @{$connected} ; $di++) {
        printf("[%d] %s\n", $di, FIJI::Netlist->_connection_tostr(@{$connected}[$di]));
    }
    printf("[x] none of the above.\n", $di);
    my $sel;
    while (1) {
        $sel = <STDIN>;
        if ($sel =~ m/[0-9]+/ && defined @{$connected}[$sel]) {
            last;
        } elsif ($sel =~ m/[xX]/) {
            my $msg = "No driver selected for net " . $net->name;
            return $msg;
        } else {
            print "Invalid driver.\n";
        }
    }
    return @{$connected}[$sel];
}

## @method private _connection_tostr ($connection,$conn_str_list_ref)
# @brief Stringifies a connection information
#
# The string is in the format \<TYPE\>: \<PATH|TO|Netname\>
# Where '|' can be any HIERSEP and TYPE is one of {PIN, PORT, ASSIGN}
# and optionally pushes a hash {path=>...,type=>...,} onto the list @$conn_str_list_ref
#
# @param connection          the connection to print
# @param conn_str_list_ref   optional list where a hash describing the connection is pushed
#
# @returns STRING  in the format \<TYPE\>: \<PATH|TO|Netname\>
sub _connection_tostr {
    my ($self, $connection, $conn_str_list_ref) = @_;
    my $path;
    my $type;
    my $str;

    if (ref($connection) eq "Verilog::Netlist::Pin") {
        $path = $connection->cell->module->name . HIERSEP . $connection->cell->name . HIERSEP . $connection->name;
        $type = "PIN";
        $str = $type . ": " . $path
    } elsif (ref($connection) eq "Verilog::Netlist::Port") {
        $path = $connection->module->name . HIERSEP . $connection->name;
        $type = "PORT";
        $str = $type . ": " . $path
    } elsif (ref($connection) eq "Verilog::Netlist::ContAssign") {
        $path = $connection->module->name . HIERSEP . $connection->rhs;
        $type = "ASSIGN";
        $str = $type . ": " . $connection->rhs;
    }
    push @{$conn_str_list_ref}, {path => $path, type => $type} if defined $conn_str_list_ref;
    return $str
}

## @method public get_connection_object ($connection_path,$connection_type)
# @brief Retrieves the connection object specified by path and type
#
# Retrieves a reference to the Verilog::Pin, Verilog::Port or Verilog::ContAssign
# Object specified by the parameters
#
# @param connection_path     the hierarchichal PATH|To|the|object
# @param connection_type     the type of the object {PIN,PORT,ASSIGN}
#
# @returns the Verilog::Pin, Verilog::Port or Verilog::ContAssign Object specified by the parameters
sub get_connection_object {
    my $logger = get_logger("");
    my ($self, $connection_path, $connection_type) = @_;

    my $rv;
    my $SEP = HIERSEP;

    if ($connection_type eq "PIN") {
        if ($connection_path =~ /^(.+)\Q$SEP\E(.+)\Q$SEP\E(.+)$/) {

            $logger->trace("Looking for pin named \"$3\" in cell \"$2\" of module \"$1\"...");

            my $mod  = $self->{'nl'}->find_module($1);
            my $cell = $mod->find_cell($2) if (defined $mod);
            my $pin  = $cell->find_pin($3) if (defined $cell);
            $rv = $pin;
        }
    } elsif ($connection_type eq "PORT") {
        if ($connection_path =~ /^(.+)\Q$SEP\E(.+)$/) {

            $logger->trace("Looking for port named \"$2\" in module \"$1\"...");

            my $mod = $self->{'nl'}->find_module($1);
            my $port = $mod->find_port($2) if (defined $mod);
            $rv = $port;
        }
    } elsif ($connection_type eq "ASSIGN") {
        if ($connection_path =~ /^(.+)\Q$SEP\E(.+)$/) {
            my $lhs = $2;

            $logger->trace("Looking for assignment to/from \"$2\" in module \"$1\"...");
            my $mod = $self->{'nl'}->find_module($1);

            if (defined $mod) {
                my $assign;
                for my $a (grep { $_->isa("Verilog::Netlist::ContAssign") } $mod->statements) {
                    if ($a->lhs eq $lhs || $a->rhs =~ /\Q$lhs\E/) {
                        $assign = $a;
                        $logger->trace(sprintf("Constant assignment: \"%s\" = \"%s\"", $a->lhs, $a->rhs));
                        last;
                    }
                }
                $rv = $assign;
            }
        }
    }
    $logger->warn("Could not find $connection_type \"$connection_path\"!") if !defined($rv);
    return $rv;
}


## @method private _get_net_connections ($net,$connection_hashref)
# @brief retrieves connections of a given net
#
# gets all pins, ports and assignments a net is connected to
#
# @param net_path               hierarchical path string of the net to be examined
# @param connection_hashref     a hashref where the results can be placed
#                               connection_hashref->{'drivers'} contains a list of driver cells
#                               connection_hashref->{'driven'} contains a list of driven cells
#                               connection_hashref->{'connected'} contains a list cells connected to the
#                               net but driver/driven cannot be decided
sub _get_net_connections_from_path {
    my $logger = get_logger("");
    my ($self, $net_path, $connection_hashref) = @_;
    my $net_descriptor = $self->get_netdescriptor_from_path($net_path);
    return $net_descriptor if (ref($net_descriptor) ne "HASH");
    my $net = $net_descriptor->{net};
    return $self->_get_net_connections($net, $connection_hashref, $net_descriptor->{'msb'});
}

## @method private _untie_concatenations ($concat, $arrayref)
# @brief breaks up a verilog concatenation into single net elements
#
# @param concat     string (including the {}) forming a verilog concatenation
# @return arrayref   array reference containing the individual concatenated verilog expressions in the given string
sub _untie_concatenations {
    my $logger = get_logger("");
    my ($self, $concat) = @_;

    if ($concat =~ /^\{(.+)\}$/) {
        $concat = $1;
    }
    my @net_strings;
    foreach my $net_string ($concat =~ /(.+)/g) {
        push(@net_strings, $net_string);
    }
    return \@net_strings;
}

## @method private _get_net_connections ($net,$connection_hashref)
# @brief retrieves connections of a given net
#
# gets all pins, ports and assignments a net is connected to
#
# @param net                    the net to be examined
# @param connection_hashref     a hashref where the results can be placed
#                               connection_hashref->{'drivers'} contains a list of driver cells
#                               connection_hashref->{'driven'} contains a list of driven cells
#                               connection_hashref->{'connected'} contains a list cells connected to the
#                               net but driver/driven cannot be decided
# @param bit                    one bit of the net to check for connections (optional, only useful for vectored nets)
# @param driver_path            the path to the driver of this net (optional but depends on driver_type)
# @param driver_type            the type of the driver (can be PIN, PORT, ASSIGN) (optional but depends on driver_path)
sub _get_net_connections {
    my $logger = get_logger("");
    my ($self, $net, $connection_hashref, $bit, $driver_path, $driver_type) = @_;

    my $driver;
    my $pin_driver_supplied;
    my $port_driver_supplied;
    my $assign_driver_supplied;
    if (defined $driver_path && defined $driver_type) {
        $driver = $self->get_connection_object($driver_path, $driver_type);
        if (!defined($driver)) {
            return sprintf("No driver found for \"%s\".", $driver_path);
        }
        $pin_driver_supplied = $driver->isa("Verilog::Netlist::Pin");
        $port_driver_supplied = $driver->isa("Verilog::Netlist::Port");
        $assign_driver_supplied = (!$pin_driver_supplied && !$port_driver_supplied);
    }
    if (!defined($bit)) {
        $bit = "";
    }

    # We need this in regexes below, that do not execute function calls (FFS) thus create an intermediate variable.
    my $net_name = $net->name();

    my $connections = $connection_hashref;
    my @drivers     = ();
    my @driven      = ();
    my @connected   = ();
    $connections->{'drivers'}   = \@drivers;
    $connections->{'driven'}    = \@driven;
    $connections->{'connected'} = \@connected;

    # @FIXME what to do with bussed nets
    # @FIXME what to do with instantiations like that (concatenated nets):
    # input [5:0] p_nbus_byte_controller_c_state ;
    #  ...
    # .p_nbus_byte_controller_c_state (
    #                     {byte_controller_c_state[5],byte_controller_c_state[3]
    #                      ,byte_controller_c_state[2],byte_controller_c_state[1]
    #                      ,byte_controller_c_state[4],byte_controller_c_state[0]
    #                      })
    #
    # @TODO: can Verilog::Language::split_bus help us here?

    if (!$net->isa("Verilog::Netlist::Net")) {
        my $msg = "$net is no Verilog::Netlist::Net";
        $logger->error($msg);
        return $msg;
    }

    my $mod = $net->module;

    $logger->debug("Net \"" . $mod->name . HIERSEP . $net_name . "\", connections:");

    # find nets driven by continuous assignment (e.g., constant or inverter)
    foreach my $statement ($mod->statements) {