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Add appropriate hysteresis to tranif input pins. 

The tranif input pins are normally nothing special, but sometimes
they are fed back from the switch body. In this case, the control
needs to see the current *output* from the fed back port, in order
to get the results that people expect.
This commit is contained in:
Stephen Williams 2009-10-13 19:01:02 -07:00
parent 6b17dcc587
commit 33158355ba
2 changed files with 21 additions and 9 deletions
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4
tgt-vvp/draw_net_input.c
View File

@ -597,9 +597,9 @@ static void draw_net_input_x(ivl_nexus_t nex,
ivl_nexus_ptr_t nptr = ivl_nexus_ptr(nex, idx);
/* If this object is part of an island, then we'll be
making a port. If this nexus is an output to any
making a port. If this nexus is an output from any
switches in the island, then set island_input_flag to
true. Save the island cookie. */
false. Save the island cookie. */
if ( (sw = ivl_nexus_ptr_switch(nptr)) ) {
assert(island == 0 || island == ivl_switch_island(sw));
island = ivl_switch_island(sw);

26
vvp/island_tran.cc
View File

@ -74,22 +74,17 @@ static inline vvp_island_branch_tran* BRANCH_TRAN(vvp_island_branch*tmp)
void vvp_island_tran::run_island()
{
// Test to see if any of the branches are enabled. This loop
// tests the elabled inputs for all the branches and caches
// tests the enabled inputs for all the branches and caches
// the results in the enabled_flag for each branch. The
// run_test_enabled() method also clears all the processing
// flags for the branches so that we are in a good start
// state.
//
// If, after testing all the branches, none are enabled, the
// handle that special case by ignoring the island.
bool runnable = false;
for (vvp_island_branch*cur = branches_ ; cur ; cur = cur->next_branch) {
vvp_island_branch_tran*tmp = dynamic_cast<vvp_island_branch_tran*>(cur);
assert(tmp);
runnable |= tmp->run_test_enabled();
}
if (runnable == false)
return;
// Now resolve all the branches in the island.
for (vvp_island_branch*cur = branches_ ; cur ; cur = cur->next_branch) {
@ -113,9 +108,26 @@ bool vvp_island_branch_tran::run_test_enabled()
return true;
}
// Get the input that is driving this enable.
// SPECIAL NOTE: Try to get the input value from the
// *outvalue* of the port. If the enable is connected to a
// .port (instead of a .import) then there may be feedback
// going on, and we need to be looking at the resolved input,
// not the event input. For example:
//
// tranif1 (pin, X, pin);
//
// In this case, when we test the value for "pin", we need to
// look at the value that is resolved from this
// island. Reading the outvalue will do the trick.
//
// If the outvalue is nil, then we know that this port is a
// .import after all, so just read the invalue.
enabled_flag = false;
vvp_bit4_t enable_val;
if (ep->invalue.size() == 0)
if (ep->outvalue.size() != 0)
enable_val = ep->outvalue.value(0).value();
else if (ep->invalue.size() == 0)
enable_val = BIT4_Z;
else
enable_val = ep->invalue.value(0).value();