SRC/route_tree_timing.c

Go to the documentation of this file.

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

/* This module keeps track of the partial routing tree for timing-driven     *
 * routing.  The normal traceback structure doesn't provide enough info      *
 * about the partial routing during timing-driven routing, so the routines   *
 * in this module are used to keep a tree representation of the partial      *
 * routing during timing-driven routing.  This allows rapid incremental      *
 * timing analysis.  The net_delay module does timing analysis in one step   *
 * (not incrementally as pieces of the routing are added).  I could probably *
 * one day remove a lot of net_delay.c and call the corresponding routines   *
 * here, but it's useful to have a from-scratch delay calculator to check    *
 * the results of this one.                                                  */


/********************** Variables local to this module ***********************/

/* Array below allows mapping from any rr_node to any rt_node currently in   *
 * the rt_tree.                                                              */

static t_rt_node **rr_node_to_rt_node = NULL;   /* [0..num_rr_nodes-1] */

/* Frees lists for fast addition and deletion of nodes and edges. */

static t_rt_node *rt_node_free_list = NULL;
static t_linked_rt_edge *rt_edge_free_list = NULL;



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

static t_rt_node *alloc_rt_node(void);

static void free_rt_node(t_rt_node * rt_node);

static t_linked_rt_edge *alloc_linked_rt_edge(void);

static void free_linked_rt_edge(t_linked_rt_edge * rt_edge);

static t_rt_node *add_path_to_route_tree(struct s_heap *hptr,
                                         t_rt_node ** sink_rt_node_ptr);

static void load_new_path_R_upstream(t_rt_node * start_of_new_path_rt_node);

static t_rt_node *update_unbuffered_ancestors_C_downstream(t_rt_node
                                                           *
                                                           start_of_new_path_rt_node);

static void load_rt_subtree_Tdel(t_rt_node * subtree_rt_root,
                                 float Tarrival);



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

void
alloc_route_tree_timing_structs(void)
{

/* Allocates any structures needed to build the routing trees. */

    if(rr_node_to_rt_node != NULL || rt_node_free_list != NULL ||
       rt_node_free_list != NULL)
        {
            printf("Error in alloc_route_tree_timing_structs: old structures "
                   "already exist.\n");
            exit(1);
        }

    rr_node_to_rt_node = (t_rt_node **) my_malloc(num_rr_nodes *
                                                  sizeof(t_rt_node *));
}


void
free_route_tree_timing_structs(void)
{

/* Frees the structures needed to build routing trees, and really frees      *
 * (i.e. calls free) all the data on the free lists.                         */

    t_rt_node *rt_node, *next_node;
    t_linked_rt_edge *rt_edge, *next_edge;

    free(rr_node_to_rt_node);
    rr_node_to_rt_node = NULL;

    rt_node = rt_node_free_list;

    while(rt_node != NULL)
        {
            next_node = rt_node->u.next;
            free(rt_node);
            rt_node = next_node;
        }

    rt_node_free_list = NULL;

    rt_edge = rt_edge_free_list;

    while(rt_edge != NULL)
        {
            next_edge = rt_edge->next;
            free(rt_edge);
            rt_edge = next_edge;
        }

    rt_edge_free_list = NULL;
}


static t_rt_node *
alloc_rt_node(void)
{

/* Allocates a new rt_node, from the free list if possible, from the free   *
 * store otherwise.                                                         */

    t_rt_node *rt_node;

    rt_node = rt_node_free_list;

    if(rt_node != NULL)
        {
            rt_node_free_list = rt_node->u.next;
        }
    else
        {
            rt_node = (t_rt_node *) my_malloc(sizeof(t_rt_node));
        }

    return (rt_node);
}


static void
free_rt_node(t_rt_node * rt_node)
{

/* Adds rt_node to the proper free list.          */

    rt_node->u.next = rt_node_free_list;
    rt_node_free_list = rt_node;
}


static t_linked_rt_edge *
alloc_linked_rt_edge(void)
{

/* Allocates a new linked_rt_edge, from the free list if possible, from the  *
 * free store otherwise.                                                     */

    t_linked_rt_edge *linked_rt_edge;

    linked_rt_edge = rt_edge_free_list;

    if(linked_rt_edge != NULL)
        {
            rt_edge_free_list = linked_rt_edge->next;
        }
    else
        {
            linked_rt_edge = (t_linked_rt_edge *) my_malloc(sizeof
                                                            (t_linked_rt_edge));
        }

    return (linked_rt_edge);
}


static void
free_linked_rt_edge(t_linked_rt_edge * rt_edge)
{

/* Adds the rt_edge to the rt_edge free list.                       */

    rt_edge->next = rt_edge_free_list;
    rt_edge_free_list = rt_edge;
}


t_rt_node *
init_route_tree_to_source(int inet)
{

/* Initializes the routing tree to just the net source, and returns the root *
 * node of the rt_tree (which is just the net source).                       */

    t_rt_node *rt_root;
    int inode;

    rt_root = alloc_rt_node();
    rt_root->u.child_list = NULL;
    rt_root->parent_node = NULL;
    rt_root->parent_switch = OPEN;
    rt_root->re_expand = TRUE;

    inode = net_rr_terminals[inet][0];  /* Net source */

    rt_root->inode = inode;
    rt_root->C_downstream = rr_node[inode].C;
    rt_root->R_upstream = rr_node[inode].R;
    rt_root->Tdel = 0.5 * rr_node[inode].R * rr_node[inode].C;
    rr_node_to_rt_node[inode] = rt_root;

    return (rt_root);
}


t_rt_node *
update_route_tree(struct s_heap * hptr)
{

/* Adds the most recently finished wire segment to the routing tree, and    *
 * updates the Tdel, etc. numbers for the rest of the routing tree.  hptr   *
 * is the heap pointer of the SINK that was reached.  This routine returns  *
 * a pointer to the rt_node of the SINK that it adds to the routing.        */

    t_rt_node *start_of_new_path_rt_node, *sink_rt_node;
    t_rt_node *unbuffered_subtree_rt_root, *subtree_parent_rt_node;
    float Tdel_start;
    short iswitch;

    start_of_new_path_rt_node = add_path_to_route_tree(hptr, &sink_rt_node);
    load_new_path_R_upstream(start_of_new_path_rt_node);
    unbuffered_subtree_rt_root =
        update_unbuffered_ancestors_C_downstream(start_of_new_path_rt_node);

    subtree_parent_rt_node = unbuffered_subtree_rt_root->parent_node;

    if(subtree_parent_rt_node != NULL)
        {                       /* Parent exists. */
            Tdel_start = subtree_parent_rt_node->Tdel;
            iswitch = unbuffered_subtree_rt_root->parent_switch;
            Tdel_start += switch_inf[iswitch].R *
                unbuffered_subtree_rt_root->C_downstream;
            Tdel_start += switch_inf[iswitch].Tdel;
        }
    else
        {                       /* Subtree starts at SOURCE */
            Tdel_start = 0.;
        }

    load_rt_subtree_Tdel(unbuffered_subtree_rt_root, Tdel_start);

    return (sink_rt_node);
}


static t_rt_node *
add_path_to_route_tree(struct s_heap *hptr,
                       t_rt_node ** sink_rt_node_ptr)
{

/* Adds the most recent wire segment, ending at the SINK indicated by hptr, *
 * to the routing tree.  It returns the first (most upstream) new rt_node,  *
 * and (via a pointer) the rt_node of the new SINK.                         */

    int inode, remaining_connections_to_sink;
    short iedge, iswitch;
    float C_downstream;
    t_rt_node *rt_node, *downstream_rt_node, *sink_rt_node;
    t_linked_rt_edge *linked_rt_edge;


    inode = hptr->index;

#ifdef DEBUG
    if(rr_node[inode].type != SINK)
        {
            printf
                ("Error in add_path_to_route_tree.  Expected type = SINK (%d).\n",
                 SINK);
            printf("Got type = %d.", rr_node[inode].type);
            exit(1);
        }
#endif

    remaining_connections_to_sink = rr_node_route_inf[inode].target_flag;
    sink_rt_node = alloc_rt_node();
    sink_rt_node->u.child_list = NULL;
    sink_rt_node->inode = inode;
    C_downstream = rr_node[inode].C;
    sink_rt_node->C_downstream = C_downstream;
    rr_node_to_rt_node[inode] = sink_rt_node;

/* In the code below I'm marking SINKs and IPINs as not to be re-expanded.  *
 * Undefine NO_ROUTE_THROUGHS if you want route-throughs or ipin doglegs.   *
 * It makes the code more efficient (though not vastly) to prune this way   *
 * when there aren't route-throughs or ipin doglegs.                        */

#define NO_ROUTE_THROUGHS 1     /* Can't route through unused FB outputs */

#ifdef NO_ROUTE_THROUGHS
    sink_rt_node->re_expand = FALSE;
#else
    if(remaining_connections_to_sink == 0)
        {                       /* Usual case */
            sink_rt_node->re_expand = TRUE;
        }

    /* Weird case.  This net connects several times to the same SINK.  Thus I   *
     * can't re_expand this node as part of the partial routing for subsequent  *
     * connections, since I need to reach it again via another path.            */

    else
        {
            sink_rt_node->re_expand = FALSE;
        }
#endif


/* Now do it's predecessor. */

    downstream_rt_node = sink_rt_node;
    inode = hptr->u.prev_node;
    iedge = hptr->prev_edge;
    iswitch = rr_node[inode].switches[iedge];

/* For all "new" nodes in the path */

    while(rr_node_route_inf[inode].prev_node != NO_PREVIOUS)
        {
            linked_rt_edge = alloc_linked_rt_edge();
            linked_rt_edge->child = downstream_rt_node;
            linked_rt_edge->iswitch = iswitch;
            linked_rt_edge->next = NULL;

            rt_node = alloc_rt_node();
            downstream_rt_node->parent_node = rt_node;
            downstream_rt_node->parent_switch = iswitch;

            rt_node->u.child_list = linked_rt_edge;
            rt_node->inode = inode;

            if(switch_inf[iswitch].buffered == FALSE)
                C_downstream += rr_node[inode].C;
            else
                C_downstream = rr_node[inode].C;

            rt_node->C_downstream = C_downstream;
            rr_node_to_rt_node[inode] = rt_node;

#ifdef NO_ROUTE_THROUGHS
            if(rr_node[inode].type == IPIN)
                rt_node->re_expand = FALSE;
            else
                rt_node->re_expand = TRUE;

#else
            if(remaining_connections_to_sink == 0)
                {               /* Normal case */
                    rt_node->re_expand = TRUE;
                }
            else
                {               /* This is the IPIN before a multiply-connected SINK */
                    rt_node->re_expand = FALSE;

                    /* Reset flag so wire segments get reused */

                    remaining_connections_to_sink = 0;
                }
#endif

            downstream_rt_node = rt_node;
            iedge = rr_node_route_inf[inode].prev_edge;
            inode = rr_node_route_inf[inode].prev_node;
            iswitch = rr_node[inode].switches[iedge];
        }

/* Inode is the join point to the old routing */

    rt_node = rr_node_to_rt_node[inode];

    linked_rt_edge = alloc_linked_rt_edge();
    linked_rt_edge->child = downstream_rt_node;
    linked_rt_edge->iswitch = iswitch;
    linked_rt_edge->next = rt_node->u.child_list;
    rt_node->u.child_list = linked_rt_edge;

    downstream_rt_node->parent_node = rt_node;
    downstream_rt_node->parent_switch = iswitch;

    *sink_rt_node_ptr = sink_rt_node;
    return (downstream_rt_node);
}


static void
load_new_path_R_upstream(t_rt_node * start_of_new_path_rt_node)
{

/* Sets the R_upstream values of all the nodes in the new path to the       *
 * correct value.                                                           */

    float R_upstream;
    int inode;
    short iswitch;
    t_rt_node *rt_node, *parent_rt_node;
    t_linked_rt_edge *linked_rt_edge;

    rt_node = start_of_new_path_rt_node;
    iswitch = rt_node->parent_switch;
    inode = rt_node->inode;
    parent_rt_node = rt_node->parent_node;

    R_upstream = switch_inf[iswitch].R + rr_node[inode].R;

    if(switch_inf[iswitch].buffered == FALSE)
        R_upstream += parent_rt_node->R_upstream;

    rt_node->R_upstream = R_upstream;

/* Note:  the traversal below makes use of the fact that this new path      *
 * really is a path (not a tree with branches) to do a traversal without    *
 * recursion, etc.                                                          */

    linked_rt_edge = rt_node->u.child_list;

    while(linked_rt_edge != NULL)
        {                       /* While SINK not reached. */

#ifdef DEBUG
            if(linked_rt_edge->next != NULL)
                {
                    printf
                        ("Error in load_new_path_R_upstream: new routing addition is\n"
                         "a tree (not a path).\n");
                    exit(1);
                }
#endif

            rt_node = linked_rt_edge->child;
            iswitch = linked_rt_edge->iswitch;
            inode = rt_node->inode;

            if(switch_inf[iswitch].buffered)
                R_upstream = switch_inf[iswitch].R + rr_node[inode].R;
            else
                R_upstream += switch_inf[iswitch].R + rr_node[inode].R;

            rt_node->R_upstream = R_upstream;
            linked_rt_edge = rt_node->u.child_list;
        }
}


static t_rt_node *
update_unbuffered_ancestors_C_downstream(t_rt_node
                                         * start_of_new_path_rt_node)
{

/* Updates the C_downstream values for the ancestors of the new path.  Once *
 * a buffered switch is found amongst the ancestors, no more ancestors are  *
 * affected.  Returns the root of the "unbuffered subtree" whose Tdel       *
 * values are affected by the new path's addition.                          */

    t_rt_node *rt_node, *parent_rt_node;
    short iswitch;
    float C_downstream_addition;

    rt_node = start_of_new_path_rt_node;
    C_downstream_addition = rt_node->C_downstream;
    parent_rt_node = rt_node->parent_node;
    iswitch = rt_node->parent_switch;

    while(parent_rt_node != NULL && switch_inf[iswitch].buffered == FALSE)
        {
            rt_node = parent_rt_node;
            rt_node->C_downstream += C_downstream_addition;
            parent_rt_node = rt_node->parent_node;
            iswitch = rt_node->parent_switch;
        }

    return (rt_node);
}


static void
load_rt_subtree_Tdel(t_rt_node * subtree_rt_root,
                     float Tarrival)
{

/* Updates the Tdel values of the subtree rooted at subtree_rt_root by      *
 * by calling itself recursively.  The C_downstream values of all the nodes *
 * must be correct before this routine is called.  Tarrival is the time at  *
 * at which the signal arrives at this node's *input*.                      */

    int inode;
    short iswitch;
    t_rt_node *child_node;
    t_linked_rt_edge *linked_rt_edge;
    float Tdel, Tchild;

    inode = subtree_rt_root->inode;

/* Assuming the downstream connections are, on average, connected halfway    *
 * along a wire segment's length.  See discussion in net_delay.c if you want *
 * to change this.                                                           */

    Tdel = Tarrival + 0.5 * subtree_rt_root->C_downstream * rr_node[inode].R;
    subtree_rt_root->Tdel = Tdel;

/* Now expand the children of this node to load their Tdel values (depth-   *
 * first pre-order traversal).                                              */

    linked_rt_edge = subtree_rt_root->u.child_list;

    while(linked_rt_edge != NULL)
        {
            iswitch = linked_rt_edge->iswitch;
            child_node = linked_rt_edge->child;

            Tchild = Tdel + switch_inf[iswitch].R * child_node->C_downstream;
            Tchild += switch_inf[iswitch].Tdel; /* Intrinsic switch delay. */
            load_rt_subtree_Tdel(child_node, Tchild);

            linked_rt_edge = linked_rt_edge->next;
        }
}


void
free_route_tree(t_rt_node * rt_node)
{

/* Puts the rt_nodes and edges in the tree rooted at rt_node back on the    *
 * free lists.  Recursive, depth-first post-order traversal.                */

    t_rt_node *child_node;
    t_linked_rt_edge *rt_edge, *next_edge;

    rt_edge = rt_node->u.child_list;

    while(rt_edge != NULL)
        {                       /* For all children */
            child_node = rt_edge->child;
            free_route_tree(child_node);
            next_edge = rt_edge->next;
            free_linked_rt_edge(rt_edge);
            rt_edge = next_edge;
        }

    free_rt_node(rt_node);
}


void
update_net_delays_from_route_tree(float *net_delay,
                                  t_rt_node ** rt_node_of_sink,
                                  int inet)
{

/* Goes through all the sinks of this net and copies their delay values from *
 * the route_tree to the net_delay array.                                    */

    int isink;
    t_rt_node *sink_rt_node;

    for(isink = 1; isink <= net[inet].num_sinks; isink++)
        {
            sink_rt_node = rt_node_of_sink[isink];
            net_delay[isink] = sink_rt_node->Tdel;
        }
}

---