SRC/net_delay.c

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#include <stdio.h>
#include "util.h"
#include "vpr_types.h"
#include "globals.h"
#include "net_delay.h"


/***************** Types and defines local to this module ********************/

struct s_linked_rc_edge
{
    struct s_rc_node *child;
    short iswitch;
    struct s_linked_rc_edge *next;
};

typedef struct s_linked_rc_edge t_linked_rc_edge;

/* Linked list listing the children of an rc_node.                           *
 * child:  Pointer to an rc_node (child of the current node).                *
 * iswitch:  Index of the switch type used to connect to the child node.     *
 * next:   Pointer to the next linked_rc_edge in the linked list (allows     *
 *         you to get the next child of the current rc_node).                */



struct s_rc_node
{
    union
    {
        t_linked_rc_edge *child_list;
        struct s_rc_node *next;
    }
    u;
    int inode;
    float C_downstream;
    float Tdel;
};

typedef struct s_rc_node t_rc_node;

/* Structure describing one node in an RC tree (used to get net delays).     *
 * u.child_list:  Pointer to a linked list of linked_rc_edge.  Each one of   *
 *                the linked list entries gives a child of this node.        *
 * u.next:  Used only when this node is on the free list.  Gives the next    *
 *          node on the free list.                                           *
 * inode:  index (ID) of the rr_node that corresponds to this rc_node.       *
 * C_downstream:  Total downstream capacitance from this rc_node.  That is,  *
 *                the total C of the subtree rooted at the current node,     *
 *                including the C of the current node.                       *
 * Tdel:  Time delay for the signal to get from the net source to this node. *
 *        Includes the time to go through this node.                         */


struct s_linked_rc_ptr
{
    struct s_rc_node *rc_node;
    struct s_linked_rc_ptr *next;
};

typedef struct s_linked_rc_ptr t_linked_rc_ptr;

/* Linked list of pointers to rc_nodes.                                      *
 * rc_node:  Pointer to an rc_node.                                          *
 * next:  Next list element.                                                 */



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

static t_rc_node *alloc_and_load_rc_tree(int inet,
                                         t_rc_node ** rc_node_free_list_ptr,
                                         t_linked_rc_edge **
                                         rc_edge_free_list_ptr,
                                         t_linked_rc_ptr *
                                         rr_node_to_rc_node);

static void add_to_rc_tree(t_rc_node * parent_rc,
                           t_rc_node * child_rc,
                           short iswitch,
                           int inode,
                           t_linked_rc_edge ** rc_edge_free_list_ptr);

static t_rc_node *alloc_rc_node(t_rc_node ** rc_node_free_list_ptr);

static void free_rc_node(t_rc_node * rc_node,
                         t_rc_node ** rc_node_free_list_ptr);

static t_linked_rc_edge *alloc_linked_rc_edge(t_linked_rc_edge
                                              ** rc_edge_free_list_ptr);

static void free_linked_rc_edge(t_linked_rc_edge * rc_edge,
                                t_linked_rc_edge ** rc_edge_free_list_ptr);

static float load_rc_tree_C(t_rc_node * rc_node);

static void load_rc_tree_T(t_rc_node * rc_node,
                           float T_arrival);

static void load_one_net_delay(float **net_delay,
                               int inet,
                               t_linked_rc_ptr * rr_node_to_rc_node);

static void load_one_constant_net_delay(float **net_delay,
                                        int inet,
                                        float delay_value);

static void free_rc_tree(t_rc_node * rc_root,
                         t_rc_node ** rc_node_free_list_ptr,
                         t_linked_rc_edge ** rc_edge_free_list_ptr);

static void reset_rr_node_to_rc_node(t_linked_rc_ptr * rr_node_to_rc_node,
                                     int inet);

static void free_rc_node_free_list(t_rc_node * rc_node_free_list);

static void free_rc_edge_free_list(t_linked_rc_edge * rc_edge_free_list);



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


float **
alloc_net_delay(struct s_linked_vptr **chunk_list_head_ptr)
{

/* Allocates space for the net_delay data structure                          *
 * [0..num_nets-1][1..num_pins-1].  I chunk the data to save space on large  *
 * problems.                                                                 */

    float **net_delay;          /* [0..num_nets-1][1..num_pins-1] */
    float *tmp_ptr;
    int inet;
    int chunk_bytes_avail;
    char *chunk_next_avail_mem;

    *chunk_list_head_ptr = NULL;
    chunk_bytes_avail = 0;
    chunk_next_avail_mem = NULL;

    net_delay = (float **)my_malloc(num_nets * sizeof(float *));

    for(inet = 0; inet < num_nets; inet++)
        {
            tmp_ptr =
                (float *)my_chunk_malloc(((net[inet].num_sinks + 1) - 1) *
                                         sizeof(float), chunk_list_head_ptr,
                                         &chunk_bytes_avail,
                                         &chunk_next_avail_mem);
                
            net_delay[inet] = tmp_ptr - 1;      /* [1..num_pins-1] */
        }

    return (net_delay);
}


void
free_net_delay(float **net_delay,
               struct s_linked_vptr **chunk_list_head_ptr)
{

/* Frees the net_delay structure.  Assumes it was chunk allocated.          */

    free(net_delay);
    free_chunk_memory(*chunk_list_head_ptr);
    *chunk_list_head_ptr = NULL;
}


void
load_net_delay_from_routing(float **net_delay)
{

/* This routine loads net_delay[0..num_nets-1][1..num_pins-1].  Each entry   *
 * is the Elmore delay from the net source to the appropriate sink.  Both    *
 * the rr_graph and the routing traceback must be completely constructed     *
 * before this routine is called, and the net_delay array must have been     *
 * allocated.                                                                */

    t_rc_node *rc_node_free_list, *rc_root;
    t_linked_rc_edge *rc_edge_free_list;
    int inet;
    t_linked_rc_ptr *rr_node_to_rc_node;        /* [0..num_rr_nodes-1]  */

    rr_node_to_rc_node = (t_linked_rc_ptr *) my_calloc(num_rr_nodes,
                                                       sizeof
                                                       (t_linked_rc_ptr));

    rc_node_free_list = NULL;
    rc_edge_free_list = NULL;

    for(inet = 0; inet < num_nets; inet++)
        {
            if(net[inet].is_global)
                {
                    load_one_constant_net_delay(net_delay, inet, 0.);
                }
            else
                {
                    rc_root = alloc_and_load_rc_tree(inet, &rc_node_free_list,
                                                     &rc_edge_free_list,
                                                     rr_node_to_rc_node);
                    load_rc_tree_C(rc_root);
                    load_rc_tree_T(rc_root, 0.);
                    load_one_net_delay(net_delay, inet, rr_node_to_rc_node);
                    free_rc_tree(rc_root, &rc_node_free_list,
                                 &rc_edge_free_list);
                    reset_rr_node_to_rc_node(rr_node_to_rc_node, inet);
                }
        }

    free_rc_node_free_list(rc_node_free_list);
    free_rc_edge_free_list(rc_edge_free_list);
    free(rr_node_to_rc_node);
}


void
load_constant_net_delay(float **net_delay,
                        float delay_value)
{

/* Loads the net_delay array with delay_value for every source - sink        *
 * connection that is not on a global resource, and with 0. for every source *
 * - sink connection on a global net.  (This can be used to allow timing     *
 * analysis before routing is done with a constant net delay model).         */

    int inet;

    for(inet = 0; inet < num_nets; inet++)
        {
            if(net[inet].is_global)
                {
                    load_one_constant_net_delay(net_delay, inet, 0.);
                }
            else
                {
                    load_one_constant_net_delay(net_delay, inet, delay_value);
                }
        }
}


static t_rc_node *
alloc_and_load_rc_tree(int inet,
                       t_rc_node ** rc_node_free_list_ptr,
                       t_linked_rc_edge ** rc_edge_free_list_ptr,
                       t_linked_rc_ptr * rr_node_to_rc_node)
{

/* Builds a tree describing the routing of net inet.  Allocates all the data *
 * and inserts all the connections in the tree.                              */

    t_rc_node *curr_rc, *prev_rc, *root_rc;
    struct s_trace *tptr;
    int inode, prev_node;
    short iswitch;
    t_linked_rc_ptr *linked_rc_ptr;

    root_rc = alloc_rc_node(rc_node_free_list_ptr);
    tptr = trace_head[inet];

    if(tptr == NULL)
        {
            printf
                ("Error in alloc_and_load_rc_tree:  Traceback for net %d doesn't "
                 "exist.\n", inet);
            exit(1);
        }

    inode = tptr->index;
    iswitch = tptr->iswitch;
    root_rc->inode = inode;
    root_rc->u.child_list = NULL;
    rr_node_to_rc_node[inode].rc_node = root_rc;

    prev_rc = root_rc;
    tptr = tptr->next;

    while(tptr != NULL)
        {
            inode = tptr->index;

/* Is this node a "stitch-in" point to part of the existing routing or a   *
 * new piece of routing along the current routing "arm?"                   */

            if(rr_node_to_rc_node[inode].rc_node == NULL)
                {               /* Part of current "arm" */
                    curr_rc = alloc_rc_node(rc_node_free_list_ptr);
                    add_to_rc_tree(prev_rc, curr_rc, iswitch, inode,
                                   rc_edge_free_list_ptr);
                    rr_node_to_rc_node[inode].rc_node = curr_rc;
                    prev_rc = curr_rc;
                }

            else if(rr_node[inode].type != SINK)
                {               /* Connection to old stuff. */

#ifdef DEBUG
                    prev_node = prev_rc->inode;
                    if(rr_node[prev_node].type != SINK)
                        {
                            printf
                                ("Error in alloc_and_load_rc_tree:  Routing of net %d is "
                                 "not a tree.\n", inet);
                            exit(1);
                        }
#endif

                    prev_rc = rr_node_to_rc_node[inode].rc_node;
                }

            else
                {               /* SINK that this net has connected to more than once. */

                    /* I can connect to a SINK node more than once in some weird architectures. *
                     * That means the routing isn't really a tree -- there is reconvergent      *
                     * fanout from two or more IPINs into one SINK.  I convert this structure   *
                     * into a true RC tree on the fly by creating a new rc_node each time I hit *
                     * the same sink.  This means I need to keep a linked list of the rc_nodes  *
                     * associated with the rr_node (inode) associated with that SINK.           */

                    curr_rc = alloc_rc_node(rc_node_free_list_ptr);
                    add_to_rc_tree(prev_rc, curr_rc, iswitch, inode,
                                   rc_edge_free_list_ptr);

                    linked_rc_ptr = (t_linked_rc_ptr *)
                        my_malloc(sizeof(t_linked_rc_ptr));
                    linked_rc_ptr->next = rr_node_to_rc_node[inode].next;
                    rr_node_to_rc_node[inode].next = linked_rc_ptr;
                    linked_rc_ptr->rc_node = curr_rc;

                    prev_rc = curr_rc;
                }
            iswitch = tptr->iswitch;
            tptr = tptr->next;
        }

    return (root_rc);
}


static void
add_to_rc_tree(t_rc_node * parent_rc,
               t_rc_node * child_rc,
               short iswitch,
               int inode,
               t_linked_rc_edge ** rc_edge_free_list_ptr)
{

/* Adds child_rc to the child list of parent_rc, and sets the switch between *
 * them to iswitch.  This routine also intitializes the child_rc properly    *
 * and sets its node value to inode.                                         */

    t_linked_rc_edge *linked_rc_edge;

    linked_rc_edge = alloc_linked_rc_edge(rc_edge_free_list_ptr);

    linked_rc_edge->next = parent_rc->u.child_list;
    parent_rc->u.child_list = linked_rc_edge;

    linked_rc_edge->child = child_rc;
    linked_rc_edge->iswitch = iswitch;

    child_rc->u.child_list = NULL;
    child_rc->inode = inode;
}


static t_rc_node *
alloc_rc_node(t_rc_node ** rc_node_free_list_ptr)
{

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

    t_rc_node *rc_node;

    rc_node = *rc_node_free_list_ptr;

    if(rc_node != NULL)
        {
            *rc_node_free_list_ptr = rc_node->u.next;
        }
    else
        {
            rc_node = (t_rc_node *) my_malloc(sizeof(t_rc_node));
        }

    return (rc_node);
}


static void
free_rc_node(t_rc_node * rc_node,
             t_rc_node ** rc_node_free_list_ptr)
{

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

    rc_node->u.next = *rc_node_free_list_ptr;
    *rc_node_free_list_ptr = rc_node;
}


static t_linked_rc_edge *
alloc_linked_rc_edge(t_linked_rc_edge ** rc_edge_free_list_ptr)
{

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

    t_linked_rc_edge *linked_rc_edge;

    linked_rc_edge = *rc_edge_free_list_ptr;

    if(linked_rc_edge != NULL)
        {
            *rc_edge_free_list_ptr = linked_rc_edge->next;
        }
    else
        {
            linked_rc_edge = (t_linked_rc_edge *) my_malloc(sizeof
                                                            (t_linked_rc_edge));
        }

    return (linked_rc_edge);
}


static void
free_linked_rc_edge(t_linked_rc_edge * rc_edge,
                    t_linked_rc_edge ** rc_edge_free_list_ptr)
{

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

    rc_edge->next = *rc_edge_free_list_ptr;
    *rc_edge_free_list_ptr = rc_edge;
}


static float
load_rc_tree_C(t_rc_node * rc_node)
{

/* Does a post-order traversal of the rc tree to load each node's           *
 * C_downstream with the proper sum of all the downstream capacitances.     *
 * This routine calls itself recursively to perform the traversal.          */

    t_linked_rc_edge *linked_rc_edge;
    t_rc_node *child_node;
    int inode;
    short iswitch;
    float C, C_downstream;

    linked_rc_edge = rc_node->u.child_list;
    inode = rc_node->inode;
    C = rr_node[inode].C;

    while(linked_rc_edge != NULL)
        {                       /* For all children */
            iswitch = linked_rc_edge->iswitch;
            child_node = linked_rc_edge->child;
            C_downstream = load_rc_tree_C(child_node);

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

            linked_rc_edge = linked_rc_edge->next;
        }

    rc_node->C_downstream = C;
    return (C);
}


static void
load_rc_tree_T(t_rc_node * rc_node,
               float T_arrival)
{

/* This routine does a pre-order depth-first traversal of the rc tree to    *
 * compute the Tdel to each node in the rc tree.  The T_arrival is the time *
 * at which the signal hits the input to this node.  This routine calls     *
 * itself recursively to perform the traversal.                             */

    float Tdel, Rmetal, Tchild;
    t_linked_rc_edge *linked_rc_edge;
    t_rc_node *child_node;
    short iswitch;
    int inode;

    Tdel = T_arrival;
    inode = rc_node->inode;
    Rmetal = rr_node[inode].R;

/* NB:  rr_node[inode].C gives the capacitance of this node, while          *
 * rc_node->C_downstream gives the unbuffered downstream capacitance rooted *
 * at this node, including the C of the node itself.  I want to multiply    *
 * the C of this node by 0.5 Rmetal, since it's a distributed RC line.      *
 * Hence 0.5 Rmetal * Cnode is a pessimistic estimate of delay (i.e. end to *
 * end).  For the downstream capacitance rooted at this node (not including *
 * the capacitance of the node itself), I assume it is, on average,         *
 * connected halfway along the line, so I also multiply by 0.5 Rmetal.  To  *
 * be totally pessimistic I would multiply the downstream part of the       *
 * capacitance by Rmetal.  Play with this equation if you like.             */

/* Rmetal is distributed so x0.5 */
    Tdel += 0.5 * rc_node->C_downstream * Rmetal;
    rc_node->Tdel = Tdel;

/* Now expand the children of this node to load their Tdel values.       */

    linked_rc_edge = rc_node->u.child_list;

    while(linked_rc_edge != NULL)
        {                       /* For all children */
            iswitch = linked_rc_edge->iswitch;
            child_node = linked_rc_edge->child;

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

            linked_rc_edge = linked_rc_edge->next;
        }
}


static void
load_one_net_delay(float **net_delay,
                   int inet,
                   t_linked_rc_ptr * rr_node_to_rc_node)
{

/* Loads the net delay array for net inet.  The rc tree for that net must  *
 * have already been completely built and loaded.                          */

    int ipin, inode;
    float Tmax;
    t_rc_node *rc_node;
    t_linked_rc_ptr *linked_rc_ptr, *next_ptr;

    for(ipin = 1; ipin < (net[inet].num_sinks + 1); ipin++)
        {

            inode = net_rr_terminals[inet][ipin];


            linked_rc_ptr = rr_node_to_rc_node[inode].next;
            rc_node = rr_node_to_rc_node[inode].rc_node;
            Tmax = rc_node->Tdel;

            /* If below only executes when one net connects several times to the      *
             * same SINK.  In this case, I can't tell which net pin each connection   *
             * to this SINK corresponds to (I can just choose arbitrarily).  To make  *
             * sure the timing behaviour converges, I pessimistically set the delay   *
             * for all of the connections to this SINK by this net to be the max. of  *
             * the delays from this net to this SINK.  NB:  This code only occurs     *
             * when a net connect more than once to the same pin class on the same    *
             * logic block.  Only a weird architecture would allow this.              */

            if(linked_rc_ptr != NULL)
                {

                    /* The first time I hit a multiply-used SINK, I choose the largest delay  *
                     * from this net to this SINK and use it for every connection to this     *
                     * SINK by this net.                                                      */

                    do
                        {
                            rc_node = linked_rc_ptr->rc_node;
                            if(rc_node->Tdel > Tmax)
                                {
                                    Tmax = rc_node->Tdel;
                                    rr_node_to_rc_node[inode].rc_node =
                                        rc_node;
                                }
                            next_ptr = linked_rc_ptr->next;
                            free(linked_rc_ptr);
                            linked_rc_ptr = next_ptr;
                        }
                    while(linked_rc_ptr != NULL);       /* End do while */

                    rr_node_to_rc_node[inode].next = NULL;
                }
            /* End of if multiply-used SINK */
            net_delay[inet][ipin] = Tmax;
        }
}


static void
load_one_constant_net_delay(float **net_delay,
                            int inet,
                            float delay_value)
{

/* Sets each entry of the net_delay array for net inet to delay_value.     */

    int ipin;

    for(ipin = 1; ipin < (net[inet].num_sinks + 1); ipin++)
        net_delay[inet][ipin] = delay_value;
}


static void
free_rc_tree(t_rc_node * rc_root,
             t_rc_node ** rc_node_free_list_ptr,
             t_linked_rc_edge ** rc_edge_free_list_ptr)
{

/* Puts the rc tree pointed to by rc_root back on the free list.  Depth-     *
 * first post-order traversal via recursion.                                 */

    t_rc_node *rc_node, *child_node;
    t_linked_rc_edge *rc_edge, *next_edge;

    rc_node = rc_root;
    rc_edge = rc_node->u.child_list;

    while(rc_edge != NULL)
        {                       /* For all children */
            child_node = rc_edge->child;
            free_rc_tree(child_node, rc_node_free_list_ptr,
                         rc_edge_free_list_ptr);
            next_edge = rc_edge->next;
            free_linked_rc_edge(rc_edge, rc_edge_free_list_ptr);
            rc_edge = next_edge;
        }

    free_rc_node(rc_node, rc_node_free_list_ptr);
}


static void
reset_rr_node_to_rc_node(t_linked_rc_ptr * rr_node_to_rc_node,
                         int inet)
{

/* Resets the rr_node_to_rc_node mapping entries that were set during       *
 * construction of the RC tree for net inet.  Any extra linked list entries *
 * added to deal with a SINK being connected to multiple times have already *
 * been freed by load_one_net_delay.                                        */

    struct s_trace *tptr;
    int inode;

    tptr = trace_head[inet];

    while(tptr != NULL)
        {
            inode = tptr->index;
            rr_node_to_rc_node[inode].rc_node = NULL;
            tptr = tptr->next;
        }
}


static void
free_rc_node_free_list(t_rc_node * rc_node_free_list)
{

/* Really frees (i.e. calls free()) all the rc_nodes on the free list.   */

    t_rc_node *rc_node, *next_node;

    rc_node = rc_node_free_list;

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



static void
free_rc_edge_free_list(t_linked_rc_edge * rc_edge_free_list)
{

/* Really frees (i.e. calls free()) all the rc_edges on the free list.   */

    t_linked_rc_edge *rc_edge, *next_edge;

    rc_edge = rc_edge_free_list;

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


void
print_net_delay(float **net_delay,
                char *fname)
{

/* Dumps the net delays into file fname.   */

    FILE *fp;
    int inet, ipin;

    fp = my_fopen(fname, "w");

    for(inet = 0; inet < num_nets; inet++)
        {
            fprintf(fp, "Net: %d.\n", inet);
            fprintf(fp, "Delays:");

            for(ipin = 1; ipin < (net[inet].num_sinks + 1); ipin++)
                fprintf(fp, " %g", net_delay[inet][ipin]);

            fprintf(fp, "\n\n");
        }

    fclose(fp);
}

---