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Fix min_slack computation, and print out critical path after routing

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This commit is contained in:
Eddie Hung 2018-07-25 22:10:26 -07:00
parent 9d489e8198
commit b211dded3f
4 changed files with 76 additions and 34 deletions
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2
common/placer1.cc
View File

@ -275,7 +275,7 @@ class SAPlacer
}
}
}
log_info("estimated Fmax = %.2f MHz\n", compute_fmax(ctx) / 1e6);
compute_fmax(ctx, true /* print_fmax */);
ctx->unlock();
return true;
}

2
common/router1.cc
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@ -815,7 +815,7 @@ bool router1(Context *ctx)
ctx->check();
ctx->unlock();
#endif
log_info("estimated Fmax = %.2f MHz\n", compute_fmax(ctx) / 1e6);
compute_fmax(ctx, true /* print_fmax */, true /* print_path */);
return true;
} catch (log_execution_error_exception) {
#ifndef NDEBUG

104
common/timing.cc
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@ -27,20 +27,24 @@
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);
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)
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;
min_slack = std::min(min_slack, value);
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;
@ -53,7 +57,7 @@ static delay_t follow_user_port(Context *ctx, PortRef &user, int path_length, de
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);
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);
}
}
@ -61,30 +65,35 @@ static delay_t follow_user_port(Context *ctx, PortRef &user, int path_length, de
}
}
auto ret = updates.emplace(&user.cell->ports.at(user.port), value);
if (!ret.second && value < ret.first->second) {
ret.first->second = value;
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)
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));
slack - ctx->getNetinfoRouteDelay(net, i), updates, min_slack, current_path, crit_path));
if (crit_path) current_path->pop_back();
}
return net_budget;
}
static UpdateMap compute_min_slack(Context *ctx, delay_t &min_slack)
static delay_t compute_min_slack(Context *ctx, UpdateMap *updates, PortRefList *crit_path)
{
UpdateMap updates;
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 ---
@ -99,18 +108,17 @@ static UpdateMap compute_min_slack(Context *ctx, delay_t &min_slack)
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);
follow_net(ctx, port.second.net, 0, slack, updates, min_slack, &current_path, crit_path);
}
}
}
}
return updates;
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
@ -121,15 +129,15 @@ void assign_budget(Context *ctx)
}
}
delay_t min_slack = default_slack;
auto updates = compute_min_slack(ctx, min_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 critical path
// 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 = %f\n", min_slack,
log_info("minimum slack for this assign = %d, target Fmax for next update = %.2f MHz\n", min_slack,
ctx->target_freq / 1e6);
}
@ -163,16 +171,18 @@ void assign_budget(Context *ctx)
void update_budget(Context *ctx)
{
UpdateMap updates;
delay_t default_slack = delay_t(1.0e12 / ctx->target_freq);
delay_t min_slack = default_slack;
auto updates = compute_min_slack(ctx, min_slack);
delay_t min_slack = compute_min_slack(ctx, &updates, nullptr);
// If user has not specified a frequency, adjust the target frequency
// to be +5% higher than the current critical path
// If user has not specified a frequency, adjust the frequency dynamically:
if (!ctx->user_freq) {
ctx->target_freq = 1.05 * (1e12 / (default_slack - min_slack));
if (min_slack < 0)
ctx->target_freq = 1e12 / (default_slack - 0.99 * min_slack);
else
ctx->target_freq = 1e12 / (default_slack - 1.05 * min_slack);
if (ctx->verbose)
log_info("minimum slack for this update = %d, target Fmax for next update = %f\n", min_slack,
log_info("minimum slack for this update = %d, target Fmax for next update = %.2f MHz\n", min_slack,
ctx->target_freq / 1e6);
}
@ -204,12 +214,44 @@ void update_budget(Context *ctx)
}
}
float compute_fmax(Context *ctx)
void compute_fmax(Context *ctx, bool print_fmax, bool print_path)
{
delay_t default_slack = delay_t(1.0e12 / ctx->target_freq);
delay_t min_slack = default_slack;
compute_min_slack(ctx, min_slack);
return 1e12 / (default_slack - min_slack);
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:\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;
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 (s)\n", comb_delay, total, driver_cell->name.c_str(ctx), driver.port.c_str(ctx));
delay_t net_delay = ctx->getNetinfoRouteDelay(net, i);
net_delay = ctx->getBudgetOverride(driver, net_delay);
total += net_delay;
log_info("%4d %4d Net %s\n", net_delay, total, net->name.c_str(ctx));
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

2
common/timing.h
View File

@ -30,7 +30,7 @@ void assign_budget(Context *ctx);
// Evenly redistribute the total path slack amongst all sinks on each path
void update_budget(Context *ctx);
float compute_fmax(Context *ctx);
void compute_fmax(Context *ctx, bool print_fmax=false, bool print_path=false);
NEXTPNR_NAMESPACE_END