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Fix VHDL value of undriven net 

This ensures an undriven net has the correct value in
the generated VHDL (either '1', '0', or 'Z').

This is a fix for pr2489116.
This commit is contained in:
Nick Gasson 2009-01-06 21:20:12 +00:00 committed by Stephen Williams
parent 02b58f6ae8
commit 50f11390b2
1 changed files with 81 additions and 0 deletions
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81
tgt-vhdl/scope.cc
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@ -125,6 +125,36 @@ static string visible_nexus_signal_name(nexus_private_t *priv, vhdl_scope *scope
return sn->sig ? get_renamed_signal(sn->sig) : sn->tmpname;
}
/*
* Calculate the signal type of a nexus. This is modified from
* draw_net_input in tgt-vvp. This also returns the width of
* the signal(s) connected to the nexus.
*/
static ivl_signal_type_t signal_type_of_nexus(ivl_nexus_t nex, int &width)
{
ivl_signal_type_t out = IVL_SIT_TRI;
width = 0;
for (unsigned idx = 0; idx < ivl_nexus_ptrs(nex); idx += 1) {
ivl_signal_type_t stype;
ivl_nexus_ptr_t ptr = ivl_nexus_ptr(nex, idx);
ivl_signal_t sig = ivl_nexus_ptr_sig(ptr);
if (sig == 0)
continue;
width = ivl_signal_width(sig);
stype = ivl_signal_type(sig);
if (stype == IVL_SIT_TRI)
continue;
if (stype == IVL_SIT_NONE)
continue;
out = stype;
}
return out;
}
/*
* Generates VHDL code to fully represent a nexus.
*/
@ -136,6 +166,9 @@ void draw_nexus(ivl_nexus_t nexus)
int nptrs = ivl_nexus_ptrs(nexus);
// Number of drivers for this nexus
int ndrivers = 0;
// First pass through connect all the signals up
for (int i = 0; i < nptrs; i++) {
ivl_nexus_ptr_t nexus_ptr = ivl_nexus_ptr(nexus, i);
@ -178,6 +211,11 @@ void draw_nexus(ivl_nexus_t nexus)
link_scope_to_nexus_tmp(priv, vhdl_scope, ss.str());
}
// If this is connected to pin-0 then this nexus is driven
// by this logic gate
if (ivl_logic_pin(log, 0) == nexus)
ndrivers++;
}
else if ((lpm = ivl_nexus_ptr_lpm(nexus_ptr))) {
ivl_scope_t lpm_scope = ivl_lpm_scope(lpm);
@ -209,6 +247,11 @@ void draw_nexus(ivl_nexus_t nexus)
link_scope_to_nexus_tmp(priv, vhdl_scope, ss.str());
}
// If this is connected to the LPM output then this nexus
// is driven by the LPM
if (ivl_lpm_q(lpm, 0) == nexus)
ndrivers++;
}
else if ((con = ivl_nexus_ptr_con(nexus_ptr))) {
if (ivl_const_type(con) == IVL_VT_REAL) {
@ -222,6 +265,44 @@ void draw_nexus(ivl_nexus_t nexus)
priv->const_driver =
new vhdl_const_bits(ivl_const_bits(con), ivl_const_width(con),
ivl_const_signed(con) != 0);
// A constant is a sort of driver
ndrivers++;
}
}
// Drive undriven nets with a constant
if (ndrivers == 0) {
char def = 0;
int width;
switch (signal_type_of_nexus(nexus, width)) {
case IVL_SIT_TRI:
def = 'Z';
break;
case IVL_SIT_TRI0:
def = '0';
break;
case IVL_SIT_TRI1:
def = '1';
break;
case IVL_SIT_TRIAND:
error("No VHDL translation for triand nets");
break;
case IVL_SIT_TRIOR:
error("No VHDL translation for trior nets");
break;
default:
;
}
if (def) {
if (width > 1)
priv->const_driver =
new vhdl_bit_spec_expr(vhdl_type::std_logic(),
new vhdl_const_bit(def));
else
priv->const_driver = new vhdl_const_bit(def);
}
}