nextpnr/common/timing.cc

/*
 *  nextpnr -- Next Generation Place and Route
 *
 *  Copyright (C) 2018  David Shah <david@symbioticeda.com>
 *
 *  Permission to use, copy, modify, and/or distribute this software for any
 *  purpose with or without fee is hereby granted, provided that the above
 *  copyright notice and this permission notice appear in all copies.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 */

#include "timing.h"
#include <algorithm>
#include <unordered_map>
#include <utility>
#include "log.h"
#include "util.h"

NEXTPNR_NAMESPACE_BEGIN

typedef std::unordered_map<const PortInfo *, delay_t> UpdateMap;
typedef std::list<const PortRef *> PortRefList;

static delay_t follow_net(Context *ctx, NetInfo *net, int path_length, delay_t slack, UpdateMap *updates,
                          delay_t &min_slack, PortRefList *current_path, PortRefList *crit_path);

// Follow a path, returning budget to annotate
static delay_t follow_user_port(Context *ctx, PortRef &user, int path_length, delay_t slack, UpdateMap *updates,
                                delay_t &min_slack, PortRefList *current_path, PortRefList *crit_path)
{
    delay_t value;
    if (ctx->getPortClock(user.cell, user.port) != IdString()) {
        // At the end of a timing path (arguably, should check setup time
        // here too)
        value = slack / path_length;
        if (slack < min_slack) {
            min_slack = slack;
            if (crit_path)
                *crit_path = *current_path;
        }
    } else {
        // Default to the path ending here, if no further paths found
        value = slack / path_length;
        // Follow outputs of the user
        for (auto port : user.cell->ports) {
            if (port.second.type == PORT_OUT) {
                delay_t comb_delay;
                // Look up delay through this path
                bool is_path = ctx->getCellDelay(user.cell, user.port, port.first, comb_delay);
                if (is_path) {
                    NetInfo *net = port.second.net;
                    if (net) {
                        delay_t path_budget = follow_net(ctx, net, path_length, slack - comb_delay, updates, min_slack,
                                                         current_path, crit_path);
                        value = std::min(value, path_budget);
                    }
                }
            }
        }
    }

    if (updates) {
        auto ret = updates->emplace(&user.cell->ports.at(user.port), value);
        if (!ret.second)
            ret.first->second = std::min(value, ret.first->second);
    }
    return value;
}

static delay_t follow_net(Context *ctx, NetInfo *net, int path_length, delay_t slack, UpdateMap *updates,
                          delay_t &min_slack, PortRefList *current_path, PortRefList *crit_path)
{
    delay_t net_budget = slack / (path_length + 1);
    for (unsigned i = 0; i < net->users.size(); ++i) {
        auto &usr = net->users[i];
        if (crit_path)
            current_path->push_back(&usr);
        net_budget = std::min(net_budget,
                              follow_user_port(ctx, usr, path_length + 1, slack - ctx->getNetinfoRouteDelay(net, i),
                                               updates, min_slack, current_path, crit_path));
        if (crit_path)
            current_path->pop_back();
    }
    return net_budget;
}

static delay_t compute_min_slack(Context *ctx, UpdateMap *updates, PortRefList *crit_path)
{
    delay_t default_slack = delay_t(1.0e12 / ctx->target_freq);
    delay_t min_slack = default_slack;

    PortRefList current_path;

    // Go through all clocked drivers and distribute the available path
    //   slack evenly into the budget of every sink on the path ---
    //   record this value into the UpdateMap
    for (auto &cell : ctx->cells) {
        for (auto port : cell.second->ports) {
            if (port.second.type == PORT_OUT) {
                IdString clock_domain = ctx->getPortClock(cell.second.get(), port.first);
                if (clock_domain != IdString()) {
                    delay_t slack = default_slack; // TODO: clock constraints
                    delay_t clkToQ;
                    if (ctx->getCellDelay(cell.second.get(), clock_domain, port.first, clkToQ))
                        slack -= clkToQ;
                    if (port.second.net)
                        follow_net(ctx, port.second.net, 0, slack, updates, min_slack, &current_path, crit_path);
                }
            }
        }
    }

    return min_slack;
}

void assign_budget(Context *ctx)
{
    log_break();
    log_info("Annotating ports with timing budgets\n");
    // Clear delays to a very high value first
    delay_t default_slack = delay_t(1.0e12 / ctx->target_freq);
    for (auto &net : ctx->nets) {
        for (auto &usr : net.second->users) {
            usr.budget = default_slack;
        }
    }

    UpdateMap updates;
    delay_t min_slack = compute_min_slack(ctx, &updates, nullptr);

    // If user has not specified a frequency, adjust the target frequency
    //   to be equivalent to the estimate Fmax
    if (!ctx->user_freq) {
        ctx->target_freq = 1e12 / (default_slack - min_slack);
        if (ctx->verbose)
            log_info("minimum slack for this assign = %d, target Fmax for next update = %.2f MHz\n", min_slack,
                     ctx->target_freq / 1e6);
    }

    // Update the budgets
    for (auto &net : ctx->nets) {
        for (size_t i = 0; i < net.second->users.size(); ++i) {
            auto &user = net.second->users[i];
            auto pi = &user.cell->ports.at(user.port);
            auto it = updates.find(pi);
            if (it == updates.end())
                continue;
            user.budget = ctx->getNetinfoRouteDelay(net.second.get(), i) - it->second;

            // Post-update check
            if (ctx->user_freq && user.budget < 0)
                log_warning("port %s.%s, connected to net '%s', has negative "
                            "timing budget of %fns\n",
                            user.cell->name.c_str(ctx), user.port.c_str(ctx), net.first.c_str(ctx),
                            ctx->getDelayNS(user.budget));
            if (ctx->verbose)
                log_info("port %s.%s, connected to net '%s', has "
                         "timing budget of %fns\n",
                         user.cell->name.c_str(ctx), user.port.c_str(ctx), net.first.c_str(ctx),
                         ctx->getDelayNS(user.budget));
        }
    }

    log_info("Checksum: 0x%08x\n", ctx->checksum());
}

void update_budget(Context *ctx)
{
    UpdateMap updates;
    delay_t default_slack = delay_t(1.0e12 / ctx->target_freq);
    delay_t min_slack = compute_min_slack(ctx, &updates, nullptr);

    // If user has not specified a frequency, adjust the frequency dynamically:
    if (!ctx->user_freq) {
        ctx->target_freq = 1e12 / (default_slack - min_slack);
        if (ctx->verbose)
            log_info("minimum slack for this update = %d, target Fmax for next update = %.2f MHz\n", min_slack,
                     ctx->target_freq / 1e6);
    }

    // Update the budgets
    for (auto &net : ctx->nets) {
        for (size_t i = 0; i < net.second->users.size(); ++i) {
            auto &user = net.second->users[i];
            auto pi = &user.cell->ports.at(user.port);
            auto it = updates.find(pi);
            if (it == updates.end())
                continue;
            user.budget = ctx->getNetinfoRouteDelay(net.second.get(), i) - it->second;

            // Post-update check
            if (ctx->verbose) {
                if (ctx->user_freq && user.budget < 0)
                    log_warning("port %s.%s, connected to net '%s', has negative "
                                "timing budget of %fns\n",
                                user.cell->name.c_str(ctx), user.port.c_str(ctx), net.first.c_str(ctx),
                                ctx->getDelayNS(user.budget));
                else
                    log_info("port %s.%s, connected to net '%s', has "
                             "timing budget of %fns\n",
                             user.cell->name.c_str(ctx), user.port.c_str(ctx), net.first.c_str(ctx),
                             ctx->getDelayNS(user.budget));
            }
        }
    }
}

void compute_fmax(Context *ctx, bool print_fmax, bool print_path)
{
    delay_t default_slack = delay_t(1.0e12 / ctx->target_freq);
    PortRefList crit_path;
    delay_t min_slack = compute_min_slack(ctx, nullptr, &crit_path);
    if (print_path) {
        delay_t total = 0;
        log_break();
        log_info("Critical path report:\n");
        log_info("curr total\n");
        auto &front = crit_path.front();
        auto &front_port = front->cell->ports.at(front->port);
        auto &front_driver = front_port.net->driver;
        auto last_port = ctx->getPortClock(front_driver.cell, front_driver.port);
        for (auto sink : crit_path) {
            auto sink_cell = sink->cell;
            auto &port = sink_cell->ports.at(sink->port);
            auto net = port.net;
            unsigned i = 0;
            for (auto &usr : net->users)
                if (&usr == sink) break;
                else ++i;
            auto &driver = net->driver;
            auto driver_cell = driver.cell;
            delay_t comb_delay;
            ctx->getCellDelay(sink_cell, last_port, driver.port, comb_delay);
            total += comb_delay;
            log_info("%4d %4d  Source %s.%s\n", comb_delay, total, driver_cell->name.c_str(ctx),
                     driver.port.c_str(ctx));
            delay_t net_delay = ctx->getNetinfoRouteDelay(net, i);
            total += net_delay;
            auto driver_loc = ctx->getBelLocation(driver_cell->bel);
            auto sink_loc = ctx->getBelLocation(sink_cell->bel);
            log_info("%4d %4d    Net %s budget %d (%d,%d) -> (%d,%d)\n", net_delay, total, net->name.c_str(ctx),
                     sink->budget, driver_loc.x, driver_loc.y, sink_loc.x, sink_loc.y);
            log_info("                Sink %s.%s\n", sink_cell->name.c_str(ctx), sink->port.c_str(ctx));
            last_port = sink->port;
        }
        log_break();
    }
    if (print_fmax)
        log_info("estimated Fmax = %.2f MHz\n", 1e6 / (default_slack - min_slack));
}

NEXTPNR_NAMESPACE_END