Initial (random) placer capability

This commit also includes changes to jsonparse to allow it to
1) recognize ports with no connection, and set their net pointers to NULL
2) recognize designs with a ports node rather than a ports_direction

The rule checker has also been modified to accommodate possible NULL netlists

The ice40 chip now also has iterator operations ++bi and bi++.

1 files changed, 19 insertions, 1 deletions

diff --git a/frontend/json/jsonparse.cc b/frontend/json/jsonparse.cc
index 41ecebd4..3d7c52ea 100644
--- a/frontend/json/jsonparse.cc
+++ b/frontend/json/jsonparse.cc
@@ -413,7 +413,25 @@ void	json_import_cell_ports(Design *design, string &modname, CellInfo *cell,
 	is_bus = (wire_group_node->data_array.size()>1);
 
 	// Now loop through all of the connections to this port.
-	for(int index=0; index < wire_group_node->data_array.size(); index++) {
+	if (wire_group_node->data_array.size() == 0) {
+		//
+		// There is/are no connections to this port.
+		//
+		// Create the port, but leave the net NULL
+		PortInfo	this_port;
+
+		//
+		this_port.name = port_info.name;
+		this_port.type = port_info.type;
+		this_port.net = NULL;
+
+		cell->ports[this_port.name] = this_port;
+
+		if (json_debug) log_info("      Port \'%s\' has no connection in \'%s\'\n",
+			this_port.name.c_str(), cell->name.c_str());
+
+	} else for(int index=0; index < wire_group_node->data_array.size();
+			index++) {
 		//
 		JsonNode	*wire_node;
 		PortInfo	this_port;