route_breadth_first.c

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#include <stdio.h>
#include "util.h"
#include "vpr_types.h"
#include "globals.h"
#include "route_export.h"
#include "route_common.h"
#include "route_breadth_first.h"

/********************* Subroutines local to this module *********************/

static boolean breadth_first_route_net(int inet, float bend_cost);

static void breadth_first_expand_trace_segment(struct s_trace *start_ptr,
        int remaining_connections_to_sink);

static void breadth_first_expand_neighbours(int inode, float pcost, int inet,
        float bend_cost);

static void breadth_first_add_source_to_heap(int inet);

/************************ Subroutine definitions ****************************/

boolean try_breadth_first_route(struct s_router_opts router_opts,
        t_ivec ** clb_opins_used_locally, int width_fac) {

    /* Iterated maze router ala Pathfinder Negotiated Congestion algorithm,  *
     * (FPGA 95 p. 111).  Returns TRUE if it can route this FPGA, FALSE if   *
     * it can't.                                                             */

    float pres_fac;
    boolean success, is_routable, rip_up_local_opins;
    int itry, inet;

    /* Usually the first iteration uses a very small (or 0) pres_fac to find  *
     * the shortest path and get a congestion map.  For fast compiles, I set  *
     * pres_fac high even for the first iteration.                            */

    pres_fac = router_opts.first_iter_pres_fac;

    for (itry = 1; itry <= router_opts.max_router_iterations; itry++) {

        for (inet = 0; inet < num_nets; inet++) {
            if (clb_net[inet].is_global == FALSE) { /* Skip global nets. */

                pathfinder_update_one_cost(trace_head[inet], -1, pres_fac);

                is_routable = breadth_first_route_net(inet,
                        router_opts.bend_cost);

                /* Impossible to route? (disconnected rr_graph) */

                if (!is_routable) {
                    vpr_printf(TIO_MESSAGE_INFO, "Routing failed.\n");
                    return (FALSE);
                }

                pathfinder_update_one_cost(trace_head[inet], 1, pres_fac);

            }
        }

        /* Make sure any CLB OPINs used up by subblocks being hooked directly     *
         * to them are reserved for that purpose.                                 */

        if (itry == 1)
            rip_up_local_opins = FALSE;
        else
            rip_up_local_opins = TRUE;

        reserve_locally_used_opins(pres_fac, rip_up_local_opins,
                clb_opins_used_locally);

        success = feasible_routing();
        if (success) {
            vpr_printf(TIO_MESSAGE_INFO, "Successfully routed after %d routing iterations.\n", itry);
            return (TRUE);
        }

        if (itry == 1)
            pres_fac = router_opts.initial_pres_fac;
        else
            pres_fac *= router_opts.pres_fac_mult;

        pres_fac = std::min(pres_fac, static_cast<float>(HUGE_POSITIVE_FLOAT / 1e5));

        pathfinder_update_cost(pres_fac, router_opts.acc_fac);
    }

    vpr_printf(TIO_MESSAGE_INFO, "Routing failed.\n");
    return (FALSE);
}

static boolean breadth_first_route_net(int inet, float bend_cost) {

    /* Uses a maze routing (Dijkstra's) algorithm to route a net.  The net       *
     * begins at the net output, and expands outward until it hits a target      *
     * pin.  The algorithm is then restarted with the entire first wire segment  *
     * included as part of the source this time.  For an n-pin net, the maze     *
     * router is invoked n-1 times to complete all the connections.  Inet is     *
     * the index of the net to be routed.  Bends are penalized by bend_cost      *
     * (which is typically zero for detailed routing and nonzero only for global *
     * routing), since global routes with lots of bends are tougher to detailed  *
     * route (using a detailed router like SEGA).                                *
     * If this routine finds that a net *cannot* be connected (due to a complete *
     * lack of potential paths, rather than congestion), it returns FALSE, as    *
     * routing is impossible on this architecture.  Otherwise it returns TRUE.   */

    int i, inode, prev_node, remaining_connections_to_sink;
    float pcost, new_pcost;
    struct s_heap *current;
    struct s_trace *tptr;

    free_traceback(inet);
    breadth_first_add_source_to_heap(inet);
    mark_ends(inet);

    tptr = NULL;
    remaining_connections_to_sink = 0;

    for (i = 1; i <= clb_net[inet].num_sinks; i++) { /* Need n-1 wires to connect n pins */
        breadth_first_expand_trace_segment(tptr, remaining_connections_to_sink);
        current = get_heap_head();

        if (current == NULL) { /* Infeasible routing.  No possible path for net. */
            vpr_printf (TIO_MESSAGE_INFO, "Cannot route net #%d (%s) to sink #%d -- no possible path.\n",
                    inet, clb_net[inet].name, i);
            reset_path_costs(); /* Clean up before leaving. */
            return (FALSE);
        }

        inode = current->index;

        while (rr_node_route_inf[inode].target_flag == 0) {
            pcost = rr_node_route_inf[inode].path_cost;
            new_pcost = current->cost;
            if (pcost > new_pcost) { /* New path is lowest cost. */
                rr_node_route_inf[inode].path_cost = new_pcost;
                prev_node = current->u.prev_node;
                rr_node_route_inf[inode].prev_node = prev_node;
                rr_node_route_inf[inode].prev_edge = current->prev_edge;

                if (pcost > 0.99 * HUGE_POSITIVE_FLOAT) /* First time touched. */
                    add_to_mod_list(&rr_node_route_inf[inode].path_cost);

                breadth_first_expand_neighbours(inode, new_pcost, inet,
                        bend_cost);
            }

            free_heap_data(current);
            current = get_heap_head();

            if (current == NULL) { /* Impossible routing. No path for net. */
                vpr_printf (TIO_MESSAGE_INFO, "Cannot route net #%d (%s) to sink #%d -- no possible path.\n",
                        inet, clb_net[inet].name, i);
                reset_path_costs();
                return (FALSE);
            }

            inode = current->index;
        }

        rr_node_route_inf[inode].target_flag--; /* Connected to this SINK. */
        remaining_connections_to_sink = rr_node_route_inf[inode].target_flag;
        tptr = update_traceback(current, inet);
        free_heap_data(current);
    }

    empty_heap();
    reset_path_costs();
    return (TRUE);
}

static void breadth_first_expand_trace_segment(struct s_trace *start_ptr,
        int remaining_connections_to_sink) {

    /* Adds all the rr_nodes in the traceback segment starting at tptr (and     *
     * continuing to the end of the traceback) to the heap with a cost of zero. *
     * This allows expansion to begin from the existing wiring.  The            *
     * remaining_connections_to_sink value is 0 if the route segment ending     *
     * at this location is the last one to connect to the SINK ending the route *
     * segment.  This is the usual case.  If it is not the last connection this *
     * net must make to this SINK, I have a hack to ensure the next connection  *
     * to this SINK goes through a different IPIN.  Without this hack, the      *
     * router would always put all the connections from this net to this SINK   *
     * through the same IPIN.  With LUTs or cluster-based logic blocks, you     *
     * should never have a net connecting to two logically-equivalent pins on   *
     * the same logic block, so the hack will never execute.  If your logic     *
     * block is an and-gate, however, nets might connect to two and-inputs on   *
     * the same logic block, and since the and-inputs are logically-equivalent, *
     * this means two connections to the same SINK.                             */

    struct s_trace *tptr, *next_ptr;
    int inode, sink_node, last_ipin_node;

    tptr = start_ptr;
    if(tptr != NULL && rr_node[tptr->index].type == SINK) {
        /* During logical equivalence case, only use one opin */
        tptr = tptr->next;
    }

    if (remaining_connections_to_sink == 0) { /* Usual case. */
        while (tptr != NULL) {
            node_to_heap(tptr->index, 0., NO_PREVIOUS, NO_PREVIOUS, OPEN, OPEN);
            tptr = tptr->next;
        }
    }

    else { /* This case never executes for most logic blocks. */

        /* Weird case.  Lots of hacks. The cleanest way to do this would be to empty *
         * the heap, update the congestion due to the partially-completed route, put *
         * the whole route so far (excluding IPINs and SINKs) on the heap with cost  *
         * 0., and expand till you hit the next SINK.  That would be slow, so I      *
         * do some hacks to enable incremental wavefront expansion instead.          */

        if (tptr == NULL)
            return; /* No route yet */

        next_ptr = tptr->next;
        last_ipin_node = OPEN; /* Stops compiler from complaining. */

        /* Can't put last SINK on heap with NO_PREVIOUS, etc, since that won't let  *
         * us reach it again.  Instead, leave the last traceback element (SINK) off *
         * the heap.                                                                */

        while (next_ptr != NULL) {
            inode = tptr->index;
            node_to_heap(inode, 0., NO_PREVIOUS, NO_PREVIOUS, OPEN, OPEN);

            if (rr_node[inode].type == IPIN)
                last_ipin_node = inode;

            tptr = next_ptr;
            next_ptr = tptr->next;
        }

        /* This will stop the IPIN node used to get to this SINK from being         *
         * reexpanded for the remainder of this net's routing.  This will make us   *
         * hook up more IPINs to this SINK (which is what we want).  If IPIN        *
         * doglegs are allowed in the graph, we won't be able to use this IPIN to   *
         * do a dogleg, since it won't be re-expanded.  Shouldn't be a big problem. */

        rr_node_route_inf[last_ipin_node].path_cost = -HUGE_POSITIVE_FLOAT;

        /* Also need to mark the SINK as having high cost, so another connection can *
         * be made to it.                                                            */

        sink_node = tptr->index;
        rr_node_route_inf[sink_node].path_cost = HUGE_POSITIVE_FLOAT;

        /* Finally, I need to remove any pending connections to this SINK via the    *
         * IPIN I just used (since they would result in congestion).  Scan through   *
         * the heap to do this.                                                      */

        invalidate_heap_entries(sink_node, last_ipin_node);
    }
}

static void breadth_first_expand_neighbours(int inode, float pcost, int inet,
        float bend_cost) {

    /* Puts all the rr_nodes adjacent to inode on the heap.  rr_nodes outside   *
     * the expanded bounding box specified in route_bb are not added to the     *
     * heap.  pcost is the path_cost to get to inode.                           */

    int iconn, to_node, num_edges;
    t_rr_type from_type, to_type;
    float tot_cost;

    num_edges = rr_node[inode].num_edges;
    for (iconn = 0; iconn < num_edges; iconn++) {
        to_node = rr_node[inode].edges[iconn];

        if (rr_node[to_node].xhigh < route_bb[inet].xmin
                || rr_node[to_node].xlow > route_bb[inet].xmax
                || rr_node[to_node].yhigh < route_bb[inet].ymin
                || rr_node[to_node].ylow > route_bb[inet].ymax)
            continue; /* Node is outside (expanded) bounding box. */

        tot_cost = pcost + get_rr_cong_cost(to_node);

        if (bend_cost != 0.) {
            from_type = rr_node[inode].type;
            to_type = rr_node[to_node].type;
            if ((from_type == CHANX && to_type == CHANY)
                    || (from_type == CHANY && to_type == CHANX))
                tot_cost += bend_cost;
        }

        node_to_heap(to_node, tot_cost, inode, iconn, OPEN, OPEN);
    }
}

static void breadth_first_add_source_to_heap(int inet) {

    /* Adds the SOURCE of this net to the heap.  Used to start a net's routing. */

    int inode;
    float cost;

    inode = net_rr_terminals[inet][0]; /* SOURCE */
    cost = get_rr_cong_cost(inode);

    node_to_heap(inode, cost, NO_PREVIOUS, NO_PREVIOUS, OPEN, OPEN);
}