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Merge pull request #4744 from YosysHQ/emil/clockgate-liberty
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clockgate: add -liberty
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@widlarizer
widlarizer authored Nov 20, 2024
2 parents 53a4ec3 + 4d96cbe commit 5b6baa3
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Showing 3 changed files with 358 additions and 8 deletions.
200 changes: 196 additions & 4 deletions passes/techmap/clockgate.cc
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Original file line number Diff line number Diff line change
@@ -1,5 +1,6 @@
#include "kernel/yosys.h"
#include "kernel/ff.h"
#include "libparse.h"
#include <optional>

USING_YOSYS_NAMESPACE
Expand All @@ -10,6 +11,7 @@ struct ClockGateCell {
IdString ce_pin;
IdString clk_in_pin;
IdString clk_out_pin;
std::vector<IdString> tie_lo_pins;
};

ClockGateCell icg_from_arg(std::string& name, std::string& str) {
Expand Down Expand Up @@ -37,6 +39,166 @@ ClockGateCell icg_from_arg(std::string& name, std::string& str) {
return c;
}

static std::pair<std::optional<ClockGateCell>, std::optional<ClockGateCell>>
find_icgs(std::string filename, std::vector<std::string> const& dont_use_cells) {
std::ifstream f;
f.open(filename.c_str());
if (f.fail())
log_cmd_error("Can't open liberty file `%s': %s\n", filename.c_str(), strerror(errno));
LibertyParser libparser(f);
f.close();
auto ast = libparser.ast;

// We will pick the most suitable ICG absed on tie_lo count and area
struct ICGRankable : public ClockGateCell { double area; };
std::optional<ICGRankable> best_pos;
std::optional<ICGRankable> best_neg;

if (ast->id != "library")
log_error("Format error in liberty file.\n");

// This is a lot of boilerplate, isn't it?
for (auto cell : ast->children)
{
if (cell->id != "cell" || cell->args.size() != 1)
continue;

const LibertyAst *dn = cell->find("dont_use");
if (dn != nullptr && dn->value == "true")
continue;

bool dont_use = false;
for (auto dont_use_cell : dont_use_cells)
{
if (patmatch(dont_use_cell.c_str(), cell->args[0].c_str()))
{
dont_use = true;
break;
}
}
if (dont_use)
continue;

const LibertyAst *icg_kind_ast = cell->find("clock_gating_integrated_cell");
if (icg_kind_ast == nullptr)
continue;

auto cell_name = cell->args[0];
auto icg_kind = icg_kind_ast->value;
auto starts_with = [&](std::string prefix) {
return icg_kind.compare(0, prefix.size(), prefix) == 0;
};
bool clk_pol;
if (icg_kind == "latch_posedge" || starts_with("latch_posedge_")) {
clk_pol = true;
} else if (icg_kind == "latch_negedge" || starts_with("latch_negedge_")) {
clk_pol = false;
} else {
log("Ignoring ICG primitive %s of kind '%s'\n", cell_name.c_str(), icg_kind.c_str());
continue;
}

log_debug("maybe valid icg: %s\n", cell_name.c_str());
ClockGateCell icg_interface;
icg_interface.name = RTLIL::escape_id(cell_name);

for (auto pin : cell->children) {
if (pin->id != "pin" || pin->args.size() != 1)
continue;

if (auto clk = pin->find("clock_gate_clock_pin")) {
if (!icg_interface.clk_in_pin.empty()) {
log_warning("Malformed liberty file - multiple clock_gate_clock_pin in cell %s\n",
cell_name.c_str());
continue;
} else
icg_interface.clk_in_pin = RTLIL::escape_id(pin->args[0]);
} else if (auto gclk = pin->find("clock_gate_out_pin")) {
if (!icg_interface.clk_out_pin.empty()) {
log_warning("Malformed liberty file - multiple clock_gate_out_pin in cell %s\n",
cell_name.c_str());
continue;
} else
icg_interface.clk_out_pin = RTLIL::escape_id(pin->args[0]);
} else if (auto en = pin->find("clock_gate_enable_pin")) {
if (!icg_interface.ce_pin.empty()) {
log_warning("Malformed liberty file - multiple clock_gate_enable_pin in cell %s\n",
cell_name.c_str());
continue;
} else
icg_interface.ce_pin = RTLIL::escape_id(pin->args[0]);
} else if (auto se = pin->find("clock_gate_test_pin")) {
icg_interface.tie_lo_pins.push_back(RTLIL::escape_id(pin->args[0]));
} else {
const LibertyAst *dir = pin->find("direction");
if (dir->value == "internal")
continue;

log_warning("Malformed liberty file - extra pin %s in cell %s\n",
pin->args[0].c_str(), cell_name.c_str());
continue;
}
}

if (icg_interface.clk_in_pin.empty()) {
log_warning("Malformed liberty file - missing clock_gate_clock_pin in cell %s",
cell_name.c_str());
continue;
}
if (icg_interface.clk_out_pin.empty()) {
log_warning("Malformed liberty file - missing clock_gate_out_pin in cell %s",
cell_name.c_str());
continue;
}
if (icg_interface.ce_pin.empty()) {
log_warning("Malformed liberty file - missing clock_gate_enable_pin in cell %s",
cell_name.c_str());
continue;
}

double area = 0;
const LibertyAst *ar = cell->find("area");
if (ar != nullptr && !ar->value.empty())
area = atof(ar->value.c_str());

std::optional<ICGRankable>& icg_to_beat = clk_pol ? best_pos : best_neg;

bool winning = false;
if (icg_to_beat) {
log_debug("ties: %zu ? %zu\n", icg_to_beat->tie_lo_pins.size(),
icg_interface.tie_lo_pins.size());
log_debug("area: %f ? %f\n", icg_to_beat->area, area);

// Prefer fewer test enables over area reduction (unlikely to matter)
auto goal = std::make_pair(icg_to_beat->tie_lo_pins.size(), icg_to_beat->area);
auto cost = std::make_pair(icg_interface.tie_lo_pins.size(), area);
winning = cost < goal;

if (winning)
log_debug("%s beats %s\n", icg_interface.name.c_str(), icg_to_beat->name.c_str());
} else {
log_debug("%s is the first of its polarity\n", icg_interface.name.c_str());
winning = true;
}
if (winning) {
ICGRankable new_icg {icg_interface, area};
icg_to_beat.emplace(new_icg);
}
}

std::optional<ClockGateCell> pos;
std::optional<ClockGateCell> neg;
if (best_pos) {
log("Selected rising edge ICG %s from Liberty file\n", best_pos->name.c_str());
pos.emplace(*best_pos);
}
if (best_neg) {
log("Selected falling edge ICG %s from Liberty file\n", best_neg->name.c_str());
neg.emplace(*best_neg);
}
return std::make_pair(pos, neg);
}

struct ClockgatePass : public Pass {
ClockgatePass() : Pass("clockgate", "extract clock gating out of flip flops") { }
void help() override {
Expand All @@ -60,12 +222,20 @@ struct ClockgatePass : public Pass {
log(" user-specified <celltype> ICG (integrated clock gating)\n");
log(" cell with ports named <ce>, <clk>, <gclk>.\n");
log(" The ICG's clock enable pin must be active high.\n");
log(" -liberty <filename>\n");
log(" If specified, ICGs will be selected from the liberty file\n");
log(" if available. Priority is given to cells with fewer tie_lo\n");
log(" inputs and smaller size. This removes the need to manually\n");
log(" specify -pos or -neg and -tie_lo.\n");
log(" -dont_use <celltype>\n");
log(" Cells <celltype> won't be considered when searching for ICGs\n");
log(" in the liberty file specified by -liberty.\n");
log(" -tie_lo <port_name>\n");
log(" Port <port_name> of the ICG will be tied to zero.\n");
log(" Intended for DFT scan-enable pins.\n");
log(" -min_net_size <n>\n");
log(" Only transform sets of at least <n> eligible FFs.\n");
// log(" \n");
log(" \n");
}

// One ICG will be generated per ClkNetInfo
Expand Down Expand Up @@ -110,7 +280,9 @@ struct ClockgatePass : public Pass {

std::optional<ClockGateCell> pos_icg_desc;
std::optional<ClockGateCell> neg_icg_desc;
std::vector<std::string> tie_lo_ports;
std::vector<std::string> tie_lo_pins;
std::string liberty_file;
std::vector<std::string> dont_use_cells;
int min_net_size = 0;

size_t argidx;
Expand All @@ -126,13 +298,33 @@ struct ClockgatePass : public Pass {
neg_icg_desc = icg_from_arg(name, rest);
}
if (args[argidx] == "-tie_lo" && argidx+1 < args.size()) {
tie_lo_ports.push_back(RTLIL::escape_id(args[++argidx]));
tie_lo_pins.push_back(RTLIL::escape_id(args[++argidx]));
}
if (args[argidx] == "-liberty" && argidx+1 < args.size()) {
liberty_file = args[++argidx];
rewrite_filename(liberty_file);
}
if (args[argidx] == "-dont_use" && argidx+1 < args.size()) {
dont_use_cells.push_back(args[++argidx]);
continue;
}
if (args[argidx] == "-min_net_size" && argidx+1 < args.size()) {
min_net_size = atoi(args[++argidx].c_str());
}
}

if (!liberty_file.empty())
std::tie(pos_icg_desc, neg_icg_desc) =
find_icgs(liberty_file, dont_use_cells);
else {
for (auto pin : tie_lo_pins) {
if (pos_icg_desc)
pos_icg_desc->tie_lo_pins.push_back(pin);
if (neg_icg_desc)
neg_icg_desc->tie_lo_pins.push_back(pin);
}
}

extra_args(args, argidx, design);

pool<Cell*> ce_ffs;
Expand Down Expand Up @@ -185,7 +377,7 @@ struct ClockgatePass : public Pass {
gclk.new_net = module->addWire(NEW_ID);
icg->setPort(matching_icg_desc->clk_out_pin, gclk.new_net);
// Tie low DFT ports like scan chain enable
for (auto port : tie_lo_ports)
for (auto port : matching_icg_desc->tie_lo_pins)
icg->setPort(port, Const(0, 1));
// Fix CE polarity if needed
if (!clk.pol_ce) {
Expand Down
107 changes: 107 additions & 0 deletions tests/techmap/clockgate.lib
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Original file line number Diff line number Diff line change
@@ -0,0 +1,107 @@
library(test) {
/* Integrated clock gating cells */
cell (pos_small_tielo) {
area : 1;
clock_gating_integrated_cell : latch_posedge_precontrol;
pin (GCLK) {
clock_gate_out_pin : true;
direction : output;
}
pin (CLK) {
clock_gate_clock_pin : true;
direction : input;
}
pin (CE) {
clock_gate_enable_pin : true;
direction : input;
}
pin (SE) {
clock_gate_test_pin : true;
direction : input;
}
}
cell (pos_big) {
area : 10;
clock_gating_integrated_cell : latch_posedge;
pin (GCLK) {
clock_gate_out_pin : true;
direction : output;
}
pin (CLK) {
clock_gate_clock_pin : true;
direction : input;
}
pin (CE) {
clock_gate_enable_pin : true;
direction : input;
}
}
cell (pos_small) {
area : 1;
clock_gating_integrated_cell : latch_posedge;
pin (GCLK) {
clock_gate_out_pin : true;
direction : output;
}
pin (CLK) {
clock_gate_clock_pin : true;
direction : input;
}
pin (CE) {
clock_gate_enable_pin : true;
direction : input;
}
}
cell (neg_big) {
area : 10;
clock_gating_integrated_cell : latch_negedge;
pin (GCLK) {
clock_gate_out_pin : true;
direction : output;
}
pin (CLK) {
clock_gate_clock_pin : true;
direction : input;
}
pin (CE) {
clock_gate_enable_pin : true;
direction : input;
}
}
cell (neg_small_tielo) {
area : 1;
clock_gating_integrated_cell : latch_negedge_precontrol;
pin (GCLK) {
clock_gate_out_pin : true;
direction : output;
}
pin (CLK) {
clock_gate_clock_pin : true;
direction : input;
}
pin (CE) {
clock_gate_enable_pin : true;
direction : input;
}
pin (SE) {
clock_gate_test_pin : true;
direction : input;
}
}
cell (neg_small) {
area : 1;
clock_gating_integrated_cell : latch_negedge;
pin (GCLK) {
clock_gate_out_pin : true;
direction : output;
}
pin (CLK) {
clock_gate_clock_pin : true;
direction : input;
}
pin (CE) {
clock_gate_enable_pin : true;
direction : input;
}
}
}
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