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If --freq not set, attempt to find max by adjusting budget so min path slack == 0

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This commit is contained in:
Eddie Hung 2018-07-24 23:19:24 -07:00
parent a69745060e
commit c71212d0e1
4 changed files with 41 additions and 11 deletions
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1
common/nextpnr.h
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@ -466,6 +466,7 @@ struct Context : Arch, DeterministicRNG
bool force = false;
bool timing_driven = true;
float target_freq = 12e6;
bool user_freq = false;
Context(ArchArgs args) : Arch(args) {}

37
common/timing.cc
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@ -28,16 +28,17 @@ NEXTPNR_NAMESPACE_BEGIN
typedef std::unordered_map<const PortInfo*, delay_t> UpdateMap;
static delay_t follow_net(Context *ctx, NetInfo *net, int path_length, delay_t slack, UpdateMap &updates);
static delay_t follow_net(Context *ctx, NetInfo *net, int path_length, delay_t slack, UpdateMap &updates, delay_t &min_slack);
// 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)
static delay_t follow_user_port(Context *ctx, PortRef &user, int path_length, delay_t slack, UpdateMap &updates, delay_t &min_slack)
{
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);
} else {
// Default to the path ending here, if no further paths found
value = slack / path_length;
@ -50,7 +51,7 @@ 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);
delay_t path_budget = follow_net(ctx, net, path_length, slack - comb_delay, updates, min_slack);
value = std::min(value, path_budget);
}
}
@ -65,12 +66,12 @@ static delay_t follow_user_port(Context *ctx, PortRef &user, int path_length, de
return value;
}
static delay_t follow_net(Context *ctx, NetInfo *net, int path_length, delay_t slack, UpdateMap &updates)
static delay_t follow_net(Context *ctx, NetInfo *net, int path_length, delay_t slack, UpdateMap &updates, delay_t &min_slack)
{
delay_t net_budget = slack / (path_length + 1);
for (unsigned i = 0; i < net->users.size(); ++i) {
auto &usr = net->users[i];
net_budget = std::min(net_budget, follow_user_port(ctx, usr, path_length + 1, slack - ctx->getNetinfoRouteDelay(net, i), updates));
net_budget = std::min(net_budget, follow_user_port(ctx, usr, path_length + 1, slack - ctx->getNetinfoRouteDelay(net, i), updates, min_slack));
}
return net_budget;
}
@ -78,6 +79,7 @@ static delay_t follow_net(Context *ctx, NetInfo *net, int path_length, delay_t s
void assign_budget(Context *ctx)
{
UpdateMap updates;
delay_t min_slack = delay_t(1.0e12 / ctx->target_freq);
log_break();
log_info("Annotating ports with timing budgets\n");
@ -88,6 +90,7 @@ void assign_budget(Context *ctx)
usr.budget = default_slack;
}
}
min_slack = default_slack;
// Go through all clocked drivers and set up paths
for (auto &cell : ctx->cells) {
for (auto port : cell.second->ports) {
@ -98,13 +101,21 @@ void assign_budget(Context *ctx)
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);
if (port.second.net) {
log_break();
follow_net(ctx, port.second.net, 0, slack, updates, min_slack);
}
}
}
}
}
if (!ctx->user_freq) {
ctx->target_freq = delay_t(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, ctx->target_freq/1e6);
}
// Update the budgets
for (auto &net : ctx->nets) {
for (size_t i = 0; i < net.second->users.size(); ++i) {
@ -135,6 +146,8 @@ 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 = delay_t(1.0e12 / ctx->target_freq);
// Go through all clocked drivers and distribute the available path slack evenly into every budget
for (auto &cell : ctx->cells) {
@ -142,17 +155,23 @@ void update_budget(Context *ctx)
if (port.second.type == PORT_OUT) {
IdString clock_domain = ctx->getPortClock(cell.second.get(), port.first);
if (clock_domain != IdString()) {
delay_t slack = delay_t(1.0e12 / ctx->target_freq); // TODO: clock constraints
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);
follow_net(ctx, port.second.net, 0, slack, updates, min_slack);
}
}
}
}
if (!ctx->user_freq) {
ctx->target_freq = delay_t(1e12 / (default_slack - min_slack));
if (ctx->verbose)
log_info("minimum slack for this update = %d, target Fmax for next update = %f\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) {

7
ecp5/main.cc
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@ -169,8 +169,13 @@ int main(int argc, char *argv[])
if (!ctx->pack() && !ctx->force)
log_error("Packing design failed.\n");
if (vm.count("freq"))
if (vm.count("freq")) {
ctx->target_freq = vm["freq"].as<double>() * 1e6;
ctx->user_freq = true;
}
else {
log_warning("Target frequency not specified. Will optimise for max frequency.\n");
}
assign_budget(ctx.get());
ctx->check();
print_utilisation(ctx.get());

7
ice40/main.cc
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@ -365,8 +365,13 @@ int main(int argc, char *argv[])
}
}
if (vm.count("freq"))
if (vm.count("freq")) {
ctx->target_freq = vm["freq"].as<double>() * 1e6;
ctx->user_freq = true;
}
else {
log_warning("Target frequency not specified. Will optimise for max frequency.\n");
}
ctx->timing_driven = true;
if (vm.count("no-tmdriv"))