123 lines
4.5 KiB
C++
123 lines
4.5 KiB
C++
/*
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* nextpnr -- Next Generation Place and Route
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*
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* Copyright (C) 2018 David Shah <david@symbioticeda.com>
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*
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* Permission to use, copy, modify, and/or distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*
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*/
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#include "timing.h"
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#include <algorithm>
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#include <unordered_map>
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#include <utility>
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#include "log.h"
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NEXTPNR_NAMESPACE_BEGIN
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static delay_t follow_net(Context *ctx, NetInfo *net, int path_length,
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delay_t slack);
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// Follow a path, returning budget to annotate
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static delay_t follow_user_port(Context *ctx, PortRef &user, int path_length,
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delay_t slack)
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{
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delay_t value;
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if (ctx->getPortClock(user.cell, user.port) != IdString()) {
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// At the end of a timing path (arguably, should check setup time
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// here too)
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value = slack / path_length;
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} else {
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// Default to the path ending here, if no further paths found
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value = slack / path_length;
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// Follow outputs of the user
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for (auto port : user.cell->ports) {
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if (port.second.type == PORT_OUT) {
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delay_t comb_delay;
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// Look up delay through this path
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bool is_path = ctx->getCellDelay(user.cell, user.port,
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port.first, comb_delay);
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if (is_path) {
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NetInfo *net = port.second.net;
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if (net) {
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delay_t path_budget = follow_net(ctx, net, path_length,
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slack - comb_delay);
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value = std::min(value, path_budget);
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}
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}
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}
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}
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}
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if (value < user.budget) {
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user.budget = value;
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}
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return value;
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}
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static delay_t follow_net(Context *ctx, NetInfo *net, int path_length,
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delay_t slack)
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{
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delay_t net_budget = slack / (path_length + 1);
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for (auto &usr : net->users) {
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net_budget = std::min(
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net_budget, follow_user_port(ctx, usr, path_length + 1, slack));
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}
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return net_budget;
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}
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void assign_budget(Context *ctx, float default_clock)
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{
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log_info("Annotating ports with timing budgets\n");
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// Clear delays to a very high value first
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delay_t default_slack = delay_t(1.0e12 / default_clock);
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for (auto net : ctx->nets) {
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for (auto &usr : net.second->users) {
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usr.budget = default_slack;
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}
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}
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// Go through all clocked drivers and set up paths
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for (auto cell : ctx->cells) {
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for (auto port : cell.second->ports) {
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if (port.second.type == PORT_OUT) {
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IdString clock_domain =
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ctx->getPortClock(cell.second, port.first);
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if (clock_domain != IdString()) {
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delay_t slack = delay_t(
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1.0e12 / default_clock); // TODO: clock constraints
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if (port.second.net)
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follow_net(ctx, port.second.net, 0, slack);
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}
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}
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}
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}
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// Post-allocation check
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for (auto net : ctx->nets) {
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for (auto user : net.second->users) {
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if (user.budget < 0)
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log_warning("port %s.%s, connected to net '%s', has negative "
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"timing budget of %fns\n",
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user.cell->name.c_str(ctx), user.port.c_str(ctx),
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net.first.c_str(ctx), ctx->getDelayNS(user.budget));
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if (ctx->verbose)
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log_info("port %s.%s, connected to net '%s', has "
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"timing budget of %fns\n",
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user.cell->name.c_str(ctx), user.port.c_str(ctx),
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net.first.c_str(ctx), ctx->getDelayNS(user.budget));
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}
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}
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}
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NEXTPNR_NAMESPACE_END
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