aboutsummaryrefslogtreecommitdiffstats
path: root/common/timing.cc
blob: 9777ab7d476e009fb37e044845e605d18a495f56 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
/*
 *  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::list<const PortRef *> PortRefList;

static delay_t follow_net(Context *ctx, NetInfo *net, int path_length, delay_t slack, bool update, 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, bool update,
                                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) {
                DelayInfo 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.maxDelay(), update,
                                                         min_slack, current_path, crit_path);
                        value = std::min(value, path_budget);
                    }
                }
            }
        }
    }
    return value;
}

static delay_t follow_net(Context *ctx, NetInfo *net, int path_length, delay_t slack, bool update, delay_t &min_slack,
                          PortRefList *current_path, PortRefList *crit_path)
{
    delay_t net_budget = slack / (path_length + 1);
    for (auto &usr : net->users) {
        if (crit_path)
            current_path->push_back(&usr);
        // If budget override is less than existing budget, then do not increment path length
        int pl = path_length + 1;
        auto budget = ctx->getBudgetOverride(net, usr, net_budget);
        if (budget < net_budget) {
            net_budget = budget;
            pl = std::max(1, path_length);
        }
        auto delay = ctx->getNetinfoRouteDelay(net, usr);
        net_budget = std::min(
                net_budget, follow_user_port(ctx, usr, pl, slack - delay, update, min_slack, current_path, crit_path));
        if (update)
            usr.budget = std::min(usr.budget, delay + net_budget);
        if (crit_path)
            current_path->pop_back();
    }
    return net_budget;
}

static delay_t walk_paths(Context *ctx, bool update, 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
    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
                    DelayInfo clkToQ;
                    if (ctx->getCellDelay(cell.second.get(), clock_domain, port.first, clkToQ))
                        slack -= clkToQ.maxDelay();
                    if (port.second.net)
                        follow_net(ctx, port.second.net, 0, slack, update, min_slack, &current_path, crit_path);
                }
            }
        }
    }

    return min_slack;
}

void assign_budget(Context *ctx, bool quiet)
{
    if (!quiet) {
        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;
        }
    }

    delay_t min_slack = walk_paths(ctx, true, nullptr);

    if (!quiet || ctx->verbose) {
        for (auto &net : ctx->nets) {
            for (auto &user : net.second->users) {
                // 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));
                else 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));
            }
        }
    }

    // For slack redistribution, if user has not specified a frequency
    //   dynamically adjust the target frequency to be the currently
    //   achieved maximum
    if (!ctx->user_freq && ctx->slack_redist_iter > 0) {
        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);
    }

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

delay_t timing_analysis(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 = walk_paths(ctx, false, &crit_path);
    if (print_path) {
        if (crit_path.empty()) {
            log_info("Design contains no timing paths\n");
        } else {
            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;
                auto &driver = net->driver;
                auto driver_cell = driver.cell;
                DelayInfo comb_delay;
                ctx->getCellDelay(sink_cell, last_port, driver.port, comb_delay);
                total += comb_delay.maxDelay();
                log_info("%4d %4d  Source %s.%s\n", comb_delay.maxDelay(), total, driver_cell->name.c_str(ctx),
                         driver.port.c_str(ctx));
                auto net_delay = ctx->getNetinfoRouteDelay(net, *sink);
                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));
    return min_slack;
}

NEXTPNR_NAMESPACE_END