route_timing.h File Reference

This graph shows which files directly or indirectly include this file:

Go to the source code of this file.

Functions
boolean	try_timing_driven_route (struct s_router_opts router_opts, float **net_delay, t_slack *slacks, t_ivec **clb_opins_used_locally, boolean timing_analysis_enabled)
boolean	timing_driven_route_net (int inet, float pres_fac, float max_criticality, float criticality_exp, float astar_fac, float bend_cost, float *pin_criticality, int *sink_order, t_rt_node **rt_node_of_sink, float *net_delay, t_slack *slacks)
void	alloc_timing_driven_route_structs (float **pin_criticality_ptr, int **sink_order_ptr, t_rt_node ***rt_node_of_sink_ptr)
void	free_timing_driven_route_structs (float *pin_criticality, int *sink_order, t_rt_node **rt_node_of_sink)

Function Documentation

void alloc_timing_driven_route_structs	(	float **	pin_criticality_ptr,
		int **	sink_order_ptr,
		t_rt_node ***	rt_node_of_sink_ptr
	)

Definition at line 253 of file route_timing.c.

                                                                 {

    /* Allocates all the structures needed only by the timing-driven router.   */

    int max_pins_per_net;
    float *pin_criticality;
    int *sink_order;
    t_rt_node **rt_node_of_sink;

    max_pins_per_net = get_max_pins_per_net();

    pin_criticality = (float *) my_malloc(
            (max_pins_per_net - 1) * sizeof(float));
    *pin_criticality_ptr = pin_criticality - 1; /* First sink is pin #1. */

    sink_order = (int *) my_malloc((max_pins_per_net - 1) * sizeof(int));
    *sink_order_ptr = sink_order - 1;

    rt_node_of_sink = (t_rt_node **) my_malloc(
            (max_pins_per_net - 1) * sizeof(t_rt_node *));
    *rt_node_of_sink_ptr = rt_node_of_sink - 1;

    alloc_route_tree_timing_structs();
}

Here is the call graph for this function:

Here is the caller graph for this function:

void free_timing_driven_route_structs	(	float *	pin_criticality,
		int *	sink_order,
		t_rt_node **	rt_node_of_sink
	)

Definition at line 279 of file route_timing.c.

                                      {

    /* Frees all the stuctures needed only by the timing-driven router.        */

    free(pin_criticality + 1); /* Starts at index 1. */
    free(sink_order + 1);
    free(rt_node_of_sink + 1);
    free_route_tree_timing_structs();
}

Here is the call graph for this function:

Here is the caller graph for this function:

boolean timing_driven_route_net	(	int	inet,
		float	pres_fac,
		float	max_criticality,
		float	criticality_exp,
		float	astar_fac,
		float	bend_cost,
		float *	pin_criticality,
		int *	sink_order,
		t_rt_node **	rt_node_of_sink,
		float *	net_delay,
		t_slack *	slacks
	)

Definition at line 307 of file route_timing.c.

                                                                          {

    /* Returns TRUE as long is found some way to hook up this net, even if that *
     * way resulted in overuse of resources (congestion).  If there is no way   *
     * to route this net, even ignoring congestion, it returns FALSE.  In this  *
     * case the rr_graph is disconnected and you can give up. If slacks = NULL, *
     * give each net a dummy criticality of 0.                                  */

    int ipin, num_sinks, itarget, target_pin, target_node, inode;
    float target_criticality, old_tcost, new_tcost, largest_criticality,
        old_back_cost, new_back_cost;
    t_rt_node *rt_root;
    struct s_heap *current;
    struct s_trace *new_route_start_tptr;
    int highfanout_rlim;

    /* Rip-up any old routing. */

    pathfinder_update_one_cost(trace_head[inet], -1, pres_fac);
    free_traceback(inet);
    
    for (ipin = 1; ipin <= clb_net[inet].num_sinks; ipin++) { 
        if (!slacks) {
            /* Use criticality of 1. This makes all nets critical.  Note: There is a big difference between setting pin criticality to 0
            compared to 1.  If pin criticality is set to 0, then the current path delay is completely ignored during routing.  By setting
            pin criticality to 1, the current path delay to the pin will always be considered and optimized for */
            pin_criticality[ipin] = 1.0;
        } else { 
#ifdef PATH_COUNTING
            /* Pin criticality is based on a weighted sum of timing and path criticalities. */  
            pin_criticality[ipin] =      ROUTE_PATH_WEIGHT  * slacks->path_criticality[inet][ipin]
                                  + (1 - ROUTE_PATH_WEIGHT) * slacks->timing_criticality[inet][ipin]; 
#else
            /* Pin criticality is based on only timing criticality. */
            pin_criticality[ipin] = slacks->timing_criticality[inet][ipin];
#endif
            /* Currently, pin criticality is between 0 and 1. Now shift it downwards 
            by 1 - max_criticality (max_criticality is 0.99 by default, so shift down
            by 0.01) and cut off at 0.  This means that all pins with small criticalities 
            (<0.01) get criticality 0 and are ignored entirely, and everything
            else becomes a bit less critical. This effect becomes more pronounced if
            max_criticality is set lower. */
            assert(pin_criticality[ipin] > -0.01 && pin_criticality[ipin] < 1.01);
            pin_criticality[ipin] = std::max(pin_criticality[ipin] - (1.0 - max_criticality), 0.0);

            /* Take pin criticality to some power (1 by default). */
            pin_criticality[ipin] = pow(pin_criticality[ipin], criticality_exp);
            
            /* Cut off pin criticality at max_criticality. */
            pin_criticality[ipin] = std::min(pin_criticality[ipin], max_criticality);
        }
    }

    num_sinks = clb_net[inet].num_sinks;
    heapsort(sink_order, pin_criticality, num_sinks, 0);

    /* Update base costs according to fanout and criticality rules */

    largest_criticality = pin_criticality[sink_order[1]];
    update_rr_base_costs(inet, largest_criticality);

    mark_ends(inet); /* Only needed to check for multiply-connected SINKs */

    rt_root = init_route_tree_to_source(inet);

    for (itarget = 1; itarget <= num_sinks; itarget++) {
        target_pin = sink_order[itarget];
        target_node = net_rr_terminals[inet][target_pin];

        target_criticality = pin_criticality[target_pin];

        highfanout_rlim = mark_node_expansion_by_bin(inet, target_node,
                rt_root);

        add_route_tree_to_heap(rt_root, target_node, target_criticality,
                astar_fac);

        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, itarget);
            reset_path_costs();
            free_route_tree(rt_root);
            return (FALSE);
        }

        inode = current->index;

        while (inode != target_node) {
            old_tcost = rr_node_route_inf[inode].path_cost;
            new_tcost = current->cost;

            if (old_tcost > 0.99 * HUGE_POSITIVE_FLOAT) /* First time touched. */
                old_back_cost = HUGE_POSITIVE_FLOAT;
            else
                old_back_cost = rr_node_route_inf[inode].backward_path_cost;

            new_back_cost = current->backward_path_cost;

            /* I only re-expand a node if both the "known" backward cost is lower  *
             * in the new expansion (this is necessary to prevent loops from       *
             * forming in the routing and causing havoc) *and* the expected total  *
             * cost to the sink is lower than the old value.  Different R_upstream *
             * values could make a path with lower back_path_cost less desirable   *
             * than one with higher cost.  Test whether or not I should disallow   *
             * re-expansion based on a higher total cost.                          */

            if (old_tcost > new_tcost && old_back_cost > new_back_cost) {
                rr_node_route_inf[inode].prev_node = current->u.prev_node;
                rr_node_route_inf[inode].prev_edge = current->prev_edge;
                rr_node_route_inf[inode].path_cost = new_tcost;
                rr_node_route_inf[inode].backward_path_cost = new_back_cost;

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

                timing_driven_expand_neighbours(current, inet, bend_cost,
                        target_criticality, target_node, astar_fac,
                        highfanout_rlim);
            }

            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, itarget);
                reset_path_costs();
                free_route_tree(rt_root);
                return (FALSE);
            }

            inode = current->index;
        }

        /* NB:  In the code below I keep two records of the partial routing:  the   *
         * traceback and the route_tree.  The route_tree enables fast recomputation *
         * of the Elmore delay to each node in the partial routing.  The traceback  *
         * lets me reuse all the routines written for breadth-first routing, which  *
         * all take a traceback structure as input.  Before this routine exits the  *
         * route_tree structure is destroyed; only the traceback is needed at that  *
         * point.                                                                   */

        rr_node_route_inf[inode].target_flag--; /* Connected to this SINK. */
        new_route_start_tptr = update_traceback(current, inet);
        rt_node_of_sink[target_pin] = update_route_tree(current);
        free_heap_data(current);
        pathfinder_update_one_cost(new_route_start_tptr, 1, pres_fac);

        empty_heap();
        reset_path_costs();
    }

    /* For later timing analysis. */

    update_net_delays_from_route_tree(net_delay, rt_node_of_sink, inet);
    free_route_tree(rt_root);
    return (TRUE);
}

Here is the call graph for this function:

Here is the caller graph for this function:

boolean try_timing_driven_route	(	struct s_router_opts	router_opts,
		float **	net_delay,
		t_slack *	slacks,
		t_ivec **	clb_opins_used_locally,
		boolean	timing_analysis_enabled
	)

Definition at line 44 of file route_timing.c.

                                                                                                                {

    /* Timing-driven routing algorithm.  The timing graph (includes slack)   *
     * must have already been allocated, and net_delay must have been allocated. *
     * Returns TRUE if the routing succeeds, FALSE otherwise.                    */

    int itry, inet, ipin, i, bends, wirelength, total_wirelength, available_wirelength, 
        segments, *net_index, *sink_order /* [1..max_pins_per_net-1] */;
    boolean success, is_routable, rip_up_local_opins;
    float *pin_criticality /* [1..max_pins_per_net-1] */, pres_fac, *sinks, 
        critical_path_delay, init_timing_criticality_val;
    t_rt_node **rt_node_of_sink; /* [1..max_pins_per_net-1] */
    clock_t begin,end;
    sinks = (float*)my_malloc(sizeof(float) * num_nets);
    net_index = (int*)my_malloc(sizeof(int) * num_nets);

    for (i = 0; i < num_nets; i++) {
        sinks[i] = clb_net[i].num_sinks;
        net_index[i] = i;
    }
    heapsort(net_index, sinks, num_nets, 1);

    alloc_timing_driven_route_structs(&pin_criticality, &sink_order,
            &rt_node_of_sink);

    /* First do one routing iteration ignoring congestion to    
    get reasonable net delay estimates. Set criticalities to 1 
    when timing analysis is on to optimize timing, and to 0 
    when timing analysis is off to optimize routability. */

    if (timing_analysis_enabled) {
        init_timing_criticality_val = 1.;
    } else {
        init_timing_criticality_val = 0.;
    }

    for (inet = 0; inet < num_nets; inet++) {
        if (clb_net[inet].is_global == FALSE) {
            for (ipin = 1; ipin <= clb_net[inet].num_sinks; ipin++)
                slacks->timing_criticality[inet][ipin] = init_timing_criticality_val;
#ifdef PATH_COUNTING
                slacks->path_criticality[inet][ipin] = init_timing_criticality_val;
#endif      
        } else { 
            /* Set delay of global signals to zero. Non-global net 
            delays are set by update_net_delays_from_route_tree() 
            inside timing_driven_route_net(), which is only called
            for non-global nets. */
            for (ipin = 1; ipin <= clb_net[inet].num_sinks; ipin++) {
                net_delay[inet][ipin] = 0.;
            }
        }
    }

    pres_fac = router_opts.first_iter_pres_fac; /* Typically 0 -> ignore cong. */

    for (itry = 1; itry <= router_opts.max_router_iterations; itry++) {
        begin = clock();
        vpr_printf(TIO_MESSAGE_INFO, "\n");
        vpr_printf(TIO_MESSAGE_INFO, "Routing iteration: %d\n", itry);

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

                is_routable = timing_driven_route_net(inet, pres_fac,
                    router_opts.max_criticality,
                    router_opts.criticality_exp, router_opts.astar_fac,
                    router_opts.bend_cost, pin_criticality,
                    sink_order, rt_node_of_sink, net_delay[inet], slacks);

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

                if (!is_routable) {
                    vpr_printf(TIO_MESSAGE_INFO, "Routing failed.\n");
                    free_timing_driven_route_structs(pin_criticality,
                            sink_order, rt_node_of_sink);
                    free(net_index);
                    free(sinks);
                    return (FALSE);
                }
            }
        }

        if (itry == 1) {
            /* Early exit code for cases where it is obvious that a successful route will not be found 
             Heuristic: If total wirelength used in first routing iteration is X% of total available wirelength, exit
             */
            total_wirelength = 0;
            available_wirelength = 0;

            for (i = 0; i < num_rr_nodes; i++) {
                if (rr_node[i].type == CHANX || rr_node[i].type == CHANY) {
                    available_wirelength += 1 + rr_node[i].xhigh
                            - rr_node[i].xlow + rr_node[i].yhigh
                            - rr_node[i].ylow;
                }
            }

            for (inet = 0; inet < num_nets; inet++) {
                if (clb_net[inet].is_global == FALSE
                        && clb_net[inet].num_sinks != 0) { /* Globals don't count. */
                    get_num_bends_and_length(inet, &bends, &wirelength,
                            &segments);

                    total_wirelength += wirelength;
                }
            }
            vpr_printf(TIO_MESSAGE_INFO, "Wire length after first iteration %d, total available wire length %d, ratio %g\n",
                    total_wirelength, available_wirelength,
                    (float) (total_wirelength) / (float) (available_wirelength));
            if ((float) (total_wirelength) / (float) (available_wirelength)> FIRST_ITER_WIRELENTH_LIMIT) {
                vpr_printf(TIO_MESSAGE_INFO, "Wire length usage ratio exceeds limit of %g, fail routing.\n",
                        FIRST_ITER_WIRELENTH_LIMIT);
                free_timing_driven_route_structs(pin_criticality, sink_order,
                        rt_node_of_sink);
                free(net_index);
                free(sinks);
                return FALSE;
            }
        }

        /* 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);

        /* Pathfinder guys quit after finding a feasible route. I may want to keep *
         * going longer, trying to improve timing.  Think about this some.         */

        success = feasible_routing();
        if (success) {
            vpr_printf(TIO_MESSAGE_INFO, "Successfully routed after %d routing iterations.\n", itry);
            free_timing_driven_route_structs(pin_criticality, sink_order, rt_node_of_sink);
#ifdef DEBUG
            timing_driven_check_net_delays(net_delay);
#endif
            free(net_index);
            free(sinks);
            return (TRUE);
        }

        if (itry == 1) {
            pres_fac = router_opts.initial_pres_fac;
            pathfinder_update_cost(pres_fac, 0.); /* Acc_fac=0 for first iter. */
        } else {
            pres_fac *= router_opts.pres_fac_mult;

            /* Avoid overflow for high iteration counts, even if acc_cost is big */
            pres_fac = std::min(pres_fac, static_cast<float>(HUGE_POSITIVE_FLOAT / 1e5));

            pathfinder_update_cost(pres_fac, router_opts.acc_fac);
        }

        if (timing_analysis_enabled) {      
            /* Update slack values by doing another timing analysis.                 *
             * Timing_driven_route_net updated the net delay values.                 */

            load_timing_graph_net_delays(net_delay);

    #ifdef HACK_LUT_PIN_SWAPPING
            do_timing_analysis(slacks, FALSE, TRUE, FALSE);
    #else
            do_timing_analysis(slacks, FALSE, FALSE, FALSE);
    #endif

            /* Print critical path delay - convert to nanoseconds. */
            critical_path_delay = get_critical_path_delay();
            vpr_printf(TIO_MESSAGE_INFO, "Critical path: %g ns\n", critical_path_delay);
        } else {
            /* If timing analysis is not enabled, make sure that the criticalities and the  *
             * net_delays stay as 0 so that wirelength can be optimized.            */
            
            for (inet = 0; inet < num_nets; inet++) {
                for (ipin = 1; ipin <= clb_net[inet].num_sinks; ipin++) {
                    slacks->timing_criticality[inet][ipin] = 0.;
#ifdef PATH_COUNTING        
                    slacks->path_criticality[inet][ipin] = 0.;      
#endif
                    net_delay[inet][ipin] = 0.;
                }
            }
        }
        
        end = clock();
        #ifdef CLOCKS_PER_SEC
            vpr_printf(TIO_MESSAGE_INFO, "Routing iteration took %g seconds.\n", (float)(end - begin) / CLOCKS_PER_SEC);
        #else
            vpr_printf(TIO_MESSAGE_INFO, "Routing iteration took %g seconds.\n", (float)(end - begin) / CLK_PER_SEC);
        #endif
        
        fflush(stdout);
    }

    vpr_printf(TIO_MESSAGE_INFO, "Routing failed.\n");
    free_timing_driven_route_structs(pin_criticality, sink_order,
            rt_node_of_sink);
    free(net_index);
    free(sinks);
    return (FALSE);
}

Here is the call graph for this function:

Here is the caller graph for this function: