vpr/src/base/constant_nets.cpp

#include "constant_nets.h"

#include "clustered_netlist.h"

#include "vtr_assert.h"

void process_constant_nets(ClusteredNetlist& nlist, e_constant_net_method method, int verbosity) {
    if (method == CONSTANT_NET_GLOBAL) {
        /*
         * Treat constant nets (e.g. gnd/vcc) as globals so they are not routed.
         * Identifying these nets as constants is more robust than the previous
         * approach (exact name match to gnd/vcc).
         *
         * Note that by not routing constant nets we are implicitly assuming that all pins
         * in the FPGA can be tied to gnd/vcc, and hence we do not need to route them.
         */
        size_t constant_net_count = 0;
        for (ClusterNetId net : nlist.nets()) {
            if (nlist.net_is_constant(net)) {
                //Mark net as global, so that it is not routed
                VTR_LOGV_WARN(verbosity > 2, "Treating constant net '%s' as global (will not be routed)\n",
                              nlist.net_name(net).c_str());
                nlist.set_net_is_ignored(net, true);
                ++constant_net_count;
            }
        }
        VTR_LOG_WARN("Treated %zu constant nets as global which will not be routed (to see net names increase packer verbosity).\n", constant_net_count);
    } else {
        VTR_ASSERT(method == CONSTANT_NET_ROUTE);
        /* Treat constants the same as any other net, so they will be routed. Note that this requires
         * they have a valid driver (e.g. constant LUT).
         *
         * TODO: We should ultimately make this architecture driven (e.g. specify which
         *       pins which can be tied to gnd/vcc), and then route from those pins to
         *       deliver any constants to those primitive input pins which can not be directly
         *       tied directly to gnd/vcc.
         */
    }
}