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yosys/passes/sat/clk2fflogic.cc

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Added clk2fflogic
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/*
* yosys -- Yosys Open SYnthesis Suite
*
Fixing old e-mail addresses and deadnames s/((Claire|Xen|Xenia|Clifford)\s+)+(Wolf|Xen)\s+<(claire|clifford)@(symbioticeda.com|clifford.at|yosyshq.com)>/Claire Xenia Wolf <claire@yosyshq.com>/gi; s/((Nina|Nak|N\.)\s+)+Engelhardt\s+<nak@(symbioticeda.com|yosyshq.com)>/N. Engelhardt <nak@yosyshq.com>/gi; s/((David)\s+)+Shah\s+<(dave|david)@(symbioticeda.com|yosyshq.com|ds0.me)>/David Shah <dave@ds0.me>/gi; s/((Miodrag)\s+)+Milanovic\s+<(miodrag|micko)@(symbioticeda.com|yosyshq.com)>/Miodrag Milanovic <micko@yosyshq.com>/gi; s,https?://www.clifford.at/yosys/,http://yosyshq.net/yosys/,g;
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* Copyright (C) 2012 Claire Xenia Wolf <claire@yosyshq.com>
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*
* 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 "kernel/yosys.h"
#include "kernel/sigtools.h"
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#include "kernel/ffinit.h"
#include "kernel/ff.h"
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#include "kernel/mem.h"
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USING_YOSYS_NAMESPACE
PRIVATE_NAMESPACE_BEGIN
clk2fflogic: Always correctly handle simultaneously changing signals This is a complete rewrite of the FF replacing code. The previous implementation tried to implement the negative hold time by wrapping async control signals individually with pulse stretching. This did not correctly model the interaction between different simultaneously changing inputs (e.g. a falling ALOAD together with a changing AD would load the changed AD instead of the value AD had when ALOAD was high; a falling CLR could mask a raising SET for one cycle; etc.). The new approach first has the logic for all updates using only sampled values followed by the logic for all updates using only current values. That way, e.g., a falling ALOAD will load the sampled AD value but a still active ALOAD will load the current AD value. The new code also has deterministic behavior for the initial state: no operation is active when that operation would depend on a specific previous signal value. This also means clk2fflogic will no longer generate any additional uninitialized FFs. I also documented the negative hold time behavior in the help message, copying the relevant part from async2sync's help messages.
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struct SampledSig {
SigSpec sampled, current;
SigSpec &operator[](bool get_current) { return get_current ? current : sampled; }
};
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struct Clk2fflogicPass : public Pass {
Clk2fflogicPass() : Pass("clk2fflogic", "convert clocked FFs to generic $ff cells") { }
Use C++11 final/override keywords.
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void help() override
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{
// |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
log("\n");
log(" clk2fflogic [options] [selection]\n");
log("\n");
log("This command replaces clocked flip-flops with generic $ff cells that use the\n");
log("implicit global clock. This is useful for formal verification of designs with\n");
log("multiple clocks.\n");
log("\n");
clk2fflogic: Always correctly handle simultaneously changing signals This is a complete rewrite of the FF replacing code. The previous implementation tried to implement the negative hold time by wrapping async control signals individually with pulse stretching. This did not correctly model the interaction between different simultaneously changing inputs (e.g. a falling ALOAD together with a changing AD would load the changed AD instead of the value AD had when ALOAD was high; a falling CLR could mask a raising SET for one cycle; etc.). The new approach first has the logic for all updates using only sampled values followed by the logic for all updates using only current values. That way, e.g., a falling ALOAD will load the sampled AD value but a still active ALOAD will load the current AD value. The new code also has deterministic behavior for the initial state: no operation is active when that operation would depend on a specific previous signal value. This also means clk2fflogic will no longer generate any additional uninitialized FFs. I also documented the negative hold time behavior in the help message, copying the relevant part from async2sync's help messages.
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log("This pass assumes negative hold time for the async FF inputs. For example when\n");
log("a reset deasserts with the clock edge, then the FF output will still drive the\n");
log("reset value in the next cycle regardless of the data-in value at the time of\n");
log("the clock edge.\n");
log("\n");
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}
clk2fflogic: Always correctly handle simultaneously changing signals This is a complete rewrite of the FF replacing code. The previous implementation tried to implement the negative hold time by wrapping async control signals individually with pulse stretching. This did not correctly model the interaction between different simultaneously changing inputs (e.g. a falling ALOAD together with a changing AD would load the changed AD instead of the value AD had when ALOAD was high; a falling CLR could mask a raising SET for one cycle; etc.). The new approach first has the logic for all updates using only sampled values followed by the logic for all updates using only current values. That way, e.g., a falling ALOAD will load the sampled AD value but a still active ALOAD will load the current AD value. The new code also has deterministic behavior for the initial state: no operation is active when that operation would depend on a specific previous signal value. This also means clk2fflogic will no longer generate any additional uninitialized FFs. I also documented the negative hold time behavior in the help message, copying the relevant part from async2sync's help messages.
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// Active-high sampled and current value of a level-triggered control signal. Initial sampled values is low/non-asserted.
SampledSig sample_control(Module *module, SigSpec sig, bool polarity, bool is_fine) {
if (!polarity) {
if (is_fine)
sig = module->NotGate(NEW_ID, sig);
else
sig = module->Not(NEW_ID, sig);
}
std::string sig_str = log_signal(sig);
sig_str.erase(std::remove(sig_str.begin(), sig_str.end(), ' '), sig_str.end());
Wire *sampled_sig = module->addWire(NEW_ID_SUFFIX(stringf("%s#sampled", sig_str.c_str())), GetSize(sig));
sampled_sig->attributes[ID::init] = RTLIL::Const(State::S0, GetSize(sig));
if (is_fine)
module->addFfGate(NEW_ID, sig, sampled_sig);
else
module->addFf(NEW_ID, sig, sampled_sig);
return {sampled_sig, sig};
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}
clk2fflogic: Always correctly handle simultaneously changing signals This is a complete rewrite of the FF replacing code. The previous implementation tried to implement the negative hold time by wrapping async control signals individually with pulse stretching. This did not correctly model the interaction between different simultaneously changing inputs (e.g. a falling ALOAD together with a changing AD would load the changed AD instead of the value AD had when ALOAD was high; a falling CLR could mask a raising SET for one cycle; etc.). The new approach first has the logic for all updates using only sampled values followed by the logic for all updates using only current values. That way, e.g., a falling ALOAD will load the sampled AD value but a still active ALOAD will load the current AD value. The new code also has deterministic behavior for the initial state: no operation is active when that operation would depend on a specific previous signal value. This also means clk2fflogic will no longer generate any additional uninitialized FFs. I also documented the negative hold time behavior in the help message, copying the relevant part from async2sync's help messages.
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// Active-high trigger signal for an edge-triggered control signal. Initial values is low/non-edge.
SigSpec sample_control_edge(Module *module, SigSpec sig, bool polarity, bool is_fine) {
std::string sig_str = log_signal(sig);
sig_str.erase(std::remove(sig_str.begin(), sig_str.end(), ' '), sig_str.end());
Wire *sampled_sig = module->addWire(NEW_ID_SUFFIX(stringf("%s#sampled", sig_str.c_str())), GetSize(sig));
sampled_sig->attributes[ID::init] = RTLIL::Const(polarity ? State::S1 : State::S0, GetSize(sig));
if (is_fine)
module->addFfGate(NEW_ID, sig, sampled_sig);
clk2fflogic: Consistently treat async control signals as negative hold. This fixes some dfflegalize equivalence checks, and breaks others — and I strongly suspect the others are due to bad support for multiple async inputs in `proc` (in particular, lack of proper support for dlatchsr and sketchy circuits on dffsr control inputs).
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else
clk2fflogic: Always correctly handle simultaneously changing signals This is a complete rewrite of the FF replacing code. The previous implementation tried to implement the negative hold time by wrapping async control signals individually with pulse stretching. This did not correctly model the interaction between different simultaneously changing inputs (e.g. a falling ALOAD together with a changing AD would load the changed AD instead of the value AD had when ALOAD was high; a falling CLR could mask a raising SET for one cycle; etc.). The new approach first has the logic for all updates using only sampled values followed by the logic for all updates using only current values. That way, e.g., a falling ALOAD will load the sampled AD value but a still active ALOAD will load the current AD value. The new code also has deterministic behavior for the initial state: no operation is active when that operation would depend on a specific previous signal value. This also means clk2fflogic will no longer generate any additional uninitialized FFs. I also documented the negative hold time behavior in the help message, copying the relevant part from async2sync's help messages.
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module->addFf(NEW_ID, sig, sampled_sig);
return module->Eqx(NEW_ID, {sampled_sig, sig}, polarity ? SigSpec {State::S0, State::S1} : SigSpec {State::S1, State::S0});
}
// Sampled and current value of a data signal.
SampledSig sample_data(Module *module, SigSpec sig, RTLIL::Const init, bool is_fine) {
std::string sig_str = log_signal(sig);
sig_str.erase(std::remove(sig_str.begin(), sig_str.end(), ' '), sig_str.end());
Wire *sampled_sig = module->addWire(NEW_ID_SUFFIX(stringf("%s#sampled", sig_str.c_str())), GetSize(sig));
sampled_sig->attributes[ID::init] = init;
if (is_fine)
module->addFfGate(NEW_ID, sig, sampled_sig);
clk2fflogic: Consistently treat async control signals as negative hold. This fixes some dfflegalize equivalence checks, and breaks others — and I strongly suspect the others are due to bad support for multiple async inputs in `proc` (in particular, lack of proper support for dlatchsr and sketchy circuits on dffsr control inputs).
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else
clk2fflogic: Always correctly handle simultaneously changing signals This is a complete rewrite of the FF replacing code. The previous implementation tried to implement the negative hold time by wrapping async control signals individually with pulse stretching. This did not correctly model the interaction between different simultaneously changing inputs (e.g. a falling ALOAD together with a changing AD would load the changed AD instead of the value AD had when ALOAD was high; a falling CLR could mask a raising SET for one cycle; etc.). The new approach first has the logic for all updates using only sampled values followed by the logic for all updates using only current values. That way, e.g., a falling ALOAD will load the sampled AD value but a still active ALOAD will load the current AD value. The new code also has deterministic behavior for the initial state: no operation is active when that operation would depend on a specific previous signal value. This also means clk2fflogic will no longer generate any additional uninitialized FFs. I also documented the negative hold time behavior in the help message, copying the relevant part from async2sync's help messages.
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module->addFf(NEW_ID, sig, sampled_sig);
return {sampled_sig, sig};
clk2fflogic: Consistently treat async control signals as negative hold. This fixes some dfflegalize equivalence checks, and breaks others — and I strongly suspect the others are due to bad support for multiple async inputs in `proc` (in particular, lack of proper support for dlatchsr and sketchy circuits on dffsr control inputs).
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}
clk2fflogic: Always correctly handle simultaneously changing signals This is a complete rewrite of the FF replacing code. The previous implementation tried to implement the negative hold time by wrapping async control signals individually with pulse stretching. This did not correctly model the interaction between different simultaneously changing inputs (e.g. a falling ALOAD together with a changing AD would load the changed AD instead of the value AD had when ALOAD was high; a falling CLR could mask a raising SET for one cycle; etc.). The new approach first has the logic for all updates using only sampled values followed by the logic for all updates using only current values. That way, e.g., a falling ALOAD will load the sampled AD value but a still active ALOAD will load the current AD value. The new code also has deterministic behavior for the initial state: no operation is active when that operation would depend on a specific previous signal value. This also means clk2fflogic will no longer generate any additional uninitialized FFs. I also documented the negative hold time behavior in the help message, copying the relevant part from async2sync's help messages.
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SigSpec mux(Module *module, SigSpec a, SigSpec b, SigSpec s, bool is_fine) {
if (is_fine)
return module->MuxGate(NEW_ID, a, b, s);
clk2fflogic: Consistently treat async control signals as negative hold. This fixes some dfflegalize equivalence checks, and breaks others — and I strongly suspect the others are due to bad support for multiple async inputs in `proc` (in particular, lack of proper support for dlatchsr and sketchy circuits on dffsr control inputs).
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else
clk2fflogic: Always correctly handle simultaneously changing signals This is a complete rewrite of the FF replacing code. The previous implementation tried to implement the negative hold time by wrapping async control signals individually with pulse stretching. This did not correctly model the interaction between different simultaneously changing inputs (e.g. a falling ALOAD together with a changing AD would load the changed AD instead of the value AD had when ALOAD was high; a falling CLR could mask a raising SET for one cycle; etc.). The new approach first has the logic for all updates using only sampled values followed by the logic for all updates using only current values. That way, e.g., a falling ALOAD will load the sampled AD value but a still active ALOAD will load the current AD value. The new code also has deterministic behavior for the initial state: no operation is active when that operation would depend on a specific previous signal value. This also means clk2fflogic will no longer generate any additional uninitialized FFs. I also documented the negative hold time behavior in the help message, copying the relevant part from async2sync's help messages.
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return module->Mux(NEW_ID, a, b, s);
}
SigSpec bitwise_sr(Module *module, SigSpec a, SigSpec s, SigSpec r, bool is_fine) {
if (is_fine)
return module->AndGate(NEW_ID, module->OrGate(NEW_ID, a, s), module->NotGate(NEW_ID, r));
clk2fflogic: Consistently treat async control signals as negative hold. This fixes some dfflegalize equivalence checks, and breaks others — and I strongly suspect the others are due to bad support for multiple async inputs in `proc` (in particular, lack of proper support for dlatchsr and sketchy circuits on dffsr control inputs).
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else
clk2fflogic: Always correctly handle simultaneously changing signals This is a complete rewrite of the FF replacing code. The previous implementation tried to implement the negative hold time by wrapping async control signals individually with pulse stretching. This did not correctly model the interaction between different simultaneously changing inputs (e.g. a falling ALOAD together with a changing AD would load the changed AD instead of the value AD had when ALOAD was high; a falling CLR could mask a raising SET for one cycle; etc.). The new approach first has the logic for all updates using only sampled values followed by the logic for all updates using only current values. That way, e.g., a falling ALOAD will load the sampled AD value but a still active ALOAD will load the current AD value. The new code also has deterministic behavior for the initial state: no operation is active when that operation would depend on a specific previous signal value. This also means clk2fflogic will no longer generate any additional uninitialized FFs. I also documented the negative hold time behavior in the help message, copying the relevant part from async2sync's help messages.
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return module->And(NEW_ID, module->Or(NEW_ID, a, s), module->Not(NEW_ID, r));
clk2fflogic: Consistently treat async control signals as negative hold. This fixes some dfflegalize equivalence checks, and breaks others — and I strongly suspect the others are due to bad support for multiple async inputs in `proc` (in particular, lack of proper support for dlatchsr and sketchy circuits on dffsr control inputs).
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}
Use C++11 final/override keywords.
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void execute(std::vector<std::string> args, RTLIL::Design *design) override
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{
// bool flag_noinit = false;
log_header(design, "Executing CLK2FFLOGIC pass (convert clocked FFs to generic $ff cells).\n");
size_t argidx;
for (argidx = 1; argidx < args.size(); argidx++)
{
// if (args[argidx] == "-noinit") {
// flag_noinit = true;
// continue;
// }
break;
}
extra_args(args, argidx, design);
for (auto module : design->selected_modules())
{
SigMap sigmap(module);
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FfInitVals initvals(&sigmap, module);
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for (auto &mem : Mem::get_selected_memories(module))
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{
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for (int i = 0; i < GetSize(mem.rd_ports); i++) {
auto &port = mem.rd_ports[i];
if (port.clk_enable)
log_error("Read port %d of memory %s.%s is clocked. This is not supported by \"clk2fflogic\"! "
"Call \"memory\" with -nordff to avoid this error.\n", i, log_id(mem.memid), log_id(module));
}
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for (int i = 0; i < GetSize(mem.wr_ports); i++)
{
auto &port = mem.wr_ports[i];
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if (!port.clk_enable)
continue;
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log("Modifying write port %d on memory %s.%s: CLK=%s, A=%s, D=%s\n",
i, log_id(module), log_id(mem.memid), log_signal(port.clk),
log_signal(port.addr), log_signal(port.data));
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Wire *past_clk = module->addWire(NEW_ID_SUFFIX(stringf("%s#%d#past_clk#%s", log_id(mem.memid), i, log_signal(port.clk))));
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past_clk->attributes[ID::init] = port.clk_polarity ? State::S1 : State::S0;
module->addFf(NEW_ID, port.clk, past_clk);
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SigSpec clock_edge_pattern;
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if (port.clk_polarity) {
clock_edge_pattern.append(State::S0);
clock_edge_pattern.append(State::S1);
} else {
clock_edge_pattern.append(State::S1);
clock_edge_pattern.append(State::S0);
}
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SigSpec clock_edge = module->Eqx(NEW_ID, {port.clk, SigSpec(past_clk)}, clock_edge_pattern);
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SigSpec en_q = module->addWire(NEW_ID_SUFFIX(stringf("%s#%d#en_q", log_id(mem.memid), i)), GetSize(port.en));
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module->addFf(NEW_ID, port.en, en_q);
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SigSpec addr_q = module->addWire(NEW_ID_SUFFIX(stringf("%s#%d#addr_q", log_id(mem.memid), i)), GetSize(port.addr));
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module->addFf(NEW_ID, port.addr, addr_q);
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SigSpec data_q = module->addWire(NEW_ID_SUFFIX(stringf("%s#%d#data_q", log_id(mem.memid), i)), GetSize(port.data));
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module->addFf(NEW_ID, port.data, data_q);
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port.clk = State::S0;
port.en = module->Mux(NEW_ID, Const(0, GetSize(en_q)), en_q, clock_edge);
port.addr = addr_q;
port.data = data_q;
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port.clk_enable = false;
port.clk_polarity = false;
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}
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mem.emit();
}
for (auto cell : vector<Cell*>(module->selected_cells()))
{
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SigSpec qval;
if (RTLIL::builtin_ff_cell_types().count(cell->type)) {
FfData ff(&initvals, cell);
Add $dlatchsr support to clk2fflogic
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kernel/ff: Refactor FfData to enable FFs with async load. - *_en is split into *_ce (clock enable) and *_aload (async load aka latch gate enable), so both can be present at once - has_d is removed - has_gclk is added (to have a clear marker for $ff) - d_is_const and val_d leftovers are removed - async2sync, clk2fflogic, opt_dff are updated to operate correctly on FFs with async load
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if (ff.has_gclk) {
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// Already a $ff or $_FF_ cell.
continue;
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}
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FfData: some refactoring. - FfData now keeps track of the module and underlying cell, if any (so calling emit on FfData created from a cell will replace the existing cell) - FfData implementation is split off to its own .cc file for faster compilation - the "flip FF data sense by inserting inverters in front and after" functionality that zinit uses is moved onto FfData class and beefed up to have dffsr support, to support more use cases
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if (ff.has_clk) {
log("Replacing %s.%s (%s): CLK=%s, D=%s, Q=%s\n",
log_id(module), log_id(cell), log_id(cell->type),
log_signal(ff.sig_clk), log_signal(ff.sig_d), log_signal(ff.sig_q));
} else if (ff.has_aload) {
log("Replacing %s.%s (%s): EN=%s, D=%s, Q=%s\n",
log_id(module), log_id(cell), log_id(cell->type),
log_signal(ff.sig_aload), log_signal(ff.sig_ad), log_signal(ff.sig_q));
} else {
// $sr.
log("Replacing %s.%s (%s): SET=%s, CLR=%s, Q=%s\n",
log_id(module), log_id(cell), log_id(cell->type),
log_signal(ff.sig_set), log_signal(ff.sig_clr), log_signal(ff.sig_q));
}
ff.remove();
clk2fflogic: Always correctly handle simultaneously changing signals This is a complete rewrite of the FF replacing code. The previous implementation tried to implement the negative hold time by wrapping async control signals individually with pulse stretching. This did not correctly model the interaction between different simultaneously changing inputs (e.g. a falling ALOAD together with a changing AD would load the changed AD instead of the value AD had when ALOAD was high; a falling CLR could mask a raising SET for one cycle; etc.). The new approach first has the logic for all updates using only sampled values followed by the logic for all updates using only current values. That way, e.g., a falling ALOAD will load the sampled AD value but a still active ALOAD will load the current AD value. The new code also has deterministic behavior for the initial state: no operation is active when that operation would depend on a specific previous signal value. This also means clk2fflogic will no longer generate any additional uninitialized FFs. I also documented the negative hold time behavior in the help message, copying the relevant part from async2sync's help messages.
2022-10-06 08:36:35 -05:00
if (ff.has_clk)
FfData: some refactoring. - FfData now keeps track of the module and underlying cell, if any (so calling emit on FfData created from a cell will replace the existing cell) - FfData implementation is split off to its own .cc file for faster compilation - the "flip FF data sense by inserting inverters in front and after" functionality that zinit uses is moved onto FfData class and beefed up to have dffsr support, to support more use cases
2021-10-06 15:16:55 -05:00
ff.unmap_ce_srst();
Added clk2fflogic
2016-10-14 07:55:07 -05:00
clk2fflogic: Always correctly handle simultaneously changing signals This is a complete rewrite of the FF replacing code. The previous implementation tried to implement the negative hold time by wrapping async control signals individually with pulse stretching. This did not correctly model the interaction between different simultaneously changing inputs (e.g. a falling ALOAD together with a changing AD would load the changed AD instead of the value AD had when ALOAD was high; a falling CLR could mask a raising SET for one cycle; etc.). The new approach first has the logic for all updates using only sampled values followed by the logic for all updates using only current values. That way, e.g., a falling ALOAD will load the sampled AD value but a still active ALOAD will load the current AD value. The new code also has deterministic behavior for the initial state: no operation is active when that operation would depend on a specific previous signal value. This also means clk2fflogic will no longer generate any additional uninitialized FFs. I also documented the negative hold time behavior in the help message, copying the relevant part from async2sync's help messages.
2022-10-06 08:36:35 -05:00
auto next_q = sample_data(module, ff.sig_q, ff.val_init, ff.is_fine).sampled;
Added clk2fflogic
2016-10-14 07:55:07 -05:00
clk2fflogic: Always correctly handle simultaneously changing signals This is a complete rewrite of the FF replacing code. The previous implementation tried to implement the negative hold time by wrapping async control signals individually with pulse stretching. This did not correctly model the interaction between different simultaneously changing inputs (e.g. a falling ALOAD together with a changing AD would load the changed AD instead of the value AD had when ALOAD was high; a falling CLR could mask a raising SET for one cycle; etc.). The new approach first has the logic for all updates using only sampled values followed by the logic for all updates using only current values. That way, e.g., a falling ALOAD will load the sampled AD value but a still active ALOAD will load the current AD value. The new code also has deterministic behavior for the initial state: no operation is active when that operation would depend on a specific previous signal value. This also means clk2fflogic will no longer generate any additional uninitialized FFs. I also documented the negative hold time behavior in the help message, copying the relevant part from async2sync's help messages.
2022-10-06 08:36:35 -05:00
if (ff.has_clk) {
// The init value for the sampled d is never used, so we can set it to fixed zero, reducing uninit'd FFs
auto sampled_d = sample_data(module, ff.sig_d, RTLIL::Const(State::S0, ff.width), ff.is_fine);
auto clk_edge = sample_control_edge(module, ff.sig_clk, ff.pol_clk, ff.is_fine);
next_q = mux(module, next_q, sampled_d.sampled, clk_edge, ff.is_fine);
kernel/ff: Refactor FfData to enable FFs with async load. - *_en is split into *_ce (clock enable) and *_aload (async load aka latch gate enable), so both can be present at once - has_d is removed - has_gclk is added (to have a clear marker for $ff) - d_is_const and val_d leftovers are removed - async2sync, clk2fflogic, opt_dff are updated to operate correctly on FFs with async load
2021-10-01 16:50:48 -05:00
}
clk2fflogic: work for bit-level $_DFF_* and $_DFFSR_*
2020-01-15 11:51:31 -06:00
clk2fflogic: Always correctly handle simultaneously changing signals This is a complete rewrite of the FF replacing code. The previous implementation tried to implement the negative hold time by wrapping async control signals individually with pulse stretching. This did not correctly model the interaction between different simultaneously changing inputs (e.g. a falling ALOAD together with a changing AD would load the changed AD instead of the value AD had when ALOAD was high; a falling CLR could mask a raising SET for one cycle; etc.). The new approach first has the logic for all updates using only sampled values followed by the logic for all updates using only current values. That way, e.g., a falling ALOAD will load the sampled AD value but a still active ALOAD will load the current AD value. The new code also has deterministic behavior for the initial state: no operation is active when that operation would depend on a specific previous signal value. This also means clk2fflogic will no longer generate any additional uninitialized FFs. I also documented the negative hold time behavior in the help message, copying the relevant part from async2sync's help messages.
2022-10-06 08:36:35 -05:00
SampledSig sampled_aload, sampled_ad, sampled_set, sampled_clr, sampled_arst;
clk2fflogic: Generate less unused logic when using verific Verific generates a lot of FFs with an unused async load and we cannot always optimize that away before running clk2fflogic, so check for that special case here.
2022-08-05 08:34:14 -05:00
// The check for a constant sig_aload is also done by opt_dff, but when using verific and running
// clk2fflogic before opt_dff (which does more and possibly unwanted optimizations) this check avoids
// generating a lot of extra logic.
clk2fflogic: Always correctly handle simultaneously changing signals This is a complete rewrite of the FF replacing code. The previous implementation tried to implement the negative hold time by wrapping async control signals individually with pulse stretching. This did not correctly model the interaction between different simultaneously changing inputs (e.g. a falling ALOAD together with a changing AD would load the changed AD instead of the value AD had when ALOAD was high; a falling CLR could mask a raising SET for one cycle; etc.). The new approach first has the logic for all updates using only sampled values followed by the logic for all updates using only current values. That way, e.g., a falling ALOAD will load the sampled AD value but a still active ALOAD will load the current AD value. The new code also has deterministic behavior for the initial state: no operation is active when that operation would depend on a specific previous signal value. This also means clk2fflogic will no longer generate any additional uninitialized FFs. I also documented the negative hold time behavior in the help message, copying the relevant part from async2sync's help messages.
2022-10-06 08:36:35 -05:00
bool has_nonconst_aload = ff.has_aload && ff.sig_aload != (ff.pol_aload ? State::S0 : State::S1);
if (has_nonconst_aload) {
sampled_aload = sample_control(module, ff.sig_aload, ff.pol_aload, ff.is_fine);
// The init value for the sampled ad is never used, so we can set it to fixed zero, reducing uninit'd FFs
sampled_ad = sample_data(module, ff.sig_ad, RTLIL::Const(State::S0, ff.width), ff.is_fine);
Added clk2fflogic
2016-10-14 07:55:07 -05:00
}
clk2fflogic: Support all FF types.
2020-07-18 20:25:41 -05:00
if (ff.has_sr) {
clk2fflogic: Always correctly handle simultaneously changing signals This is a complete rewrite of the FF replacing code. The previous implementation tried to implement the negative hold time by wrapping async control signals individually with pulse stretching. This did not correctly model the interaction between different simultaneously changing inputs (e.g. a falling ALOAD together with a changing AD would load the changed AD instead of the value AD had when ALOAD was high; a falling CLR could mask a raising SET for one cycle; etc.). The new approach first has the logic for all updates using only sampled values followed by the logic for all updates using only current values. That way, e.g., a falling ALOAD will load the sampled AD value but a still active ALOAD will load the current AD value. The new code also has deterministic behavior for the initial state: no operation is active when that operation would depend on a specific previous signal value. This also means clk2fflogic will no longer generate any additional uninitialized FFs. I also documented the negative hold time behavior in the help message, copying the relevant part from async2sync's help messages.
2022-10-06 08:36:35 -05:00
sampled_set = sample_control(module, ff.sig_set, ff.pol_set, ff.is_fine);
sampled_clr = sample_control(module, ff.sig_clr, ff.pol_clr, ff.is_fine);
}
if (ff.has_arst)
sampled_arst = sample_control(module, ff.sig_arst, ff.pol_arst, ff.is_fine);
// First perform updates using _only_ sampled values, then again using _only_ current values. Unlike the previous
// implementation, this approach correctly handles all the cases of multiple signals changing simultaneously.
for (int current = 0; current < 2; current++) {
if (has_nonconst_aload)
next_q = mux(module, next_q, sampled_ad[current], sampled_aload[current], ff.is_fine);
if (ff.has_sr)
next_q = bitwise_sr(module, next_q, sampled_set[current], sampled_clr[current], ff.is_fine);
if (ff.has_arst)
next_q = mux(module, next_q, ff.val_arst, sampled_arst[current], ff.is_fine);
Added clk2fflogic
2016-10-14 07:55:07 -05:00
}
clk2fflogic: Always correctly handle simultaneously changing signals This is a complete rewrite of the FF replacing code. The previous implementation tried to implement the negative hold time by wrapping async control signals individually with pulse stretching. This did not correctly model the interaction between different simultaneously changing inputs (e.g. a falling ALOAD together with a changing AD would load the changed AD instead of the value AD had when ALOAD was high; a falling CLR could mask a raising SET for one cycle; etc.). The new approach first has the logic for all updates using only sampled values followed by the logic for all updates using only current values. That way, e.g., a falling ALOAD will load the sampled AD value but a still active ALOAD will load the current AD value. The new code also has deterministic behavior for the initial state: no operation is active when that operation would depend on a specific previous signal value. This also means clk2fflogic will no longer generate any additional uninitialized FFs. I also documented the negative hold time behavior in the help message, copying the relevant part from async2sync's help messages.
2022-10-06 08:36:35 -05:00
module->connect(ff.sig_q, next_q);
Added clk2fflogic
2016-10-14 07:55:07 -05:00
}
}
}
}
} Clk2fflogicPass;
PRIVATE_NAMESPACE_END