Is there is any way to avoid changing manually ins...
# openroadd
Dinesh A
11/22/2021, 8:02 AMIs there is any way to avoid changing manually inserted cells during resizer phase (openroad/or_resizer.tcl) ?
repair_design -slew_margin $::env(PL_RESIZER_MAX_SLEW_MARGIN) \
-cap_margin $::env(PL_RESIZER_MAX_CAP_MARGIN)
Background: I see tool is modifying manually inserted DELAY cells to buffer.
Is there is any option to set dont touch cells to exclude manually inserted cells?
v
Vijayan Krishnan
11/22/2021, 11:28 AMset_dont_use $::env(DONT_USE_CELLS)
@User Do we have set_dont_touch for cells during runtime
d
Dinesh A
11/22/2021, 11:29 AMDONT_USE_CELLS are list cells should not be used in design
v
Vijayan Krishnan
11/22/2021, 11:30 AMset_dont_touch [get_ports *] whether this option available for cells? need to explore
Vijayan Krishnan
11/22/2021, 11:32 AMmanually inserted cells. Can you explain briefly?
d
Dinesh A
11/22/2021, 11:37 AMTypically we manually insert Standard cell for clock Mux and Internal clock source with Buffer and Interface Timing with Hold fix cells. Typically other commerical tools have option to say don't touch attribute to a instance, These instance are not touch by the tool optimization function.
Dinesh A
11/22/2021, 11:39 AMCurrently during Yosys synthesis phase, i see these cells are retained by resizer logic blindly changing the cells to higher drive buffers
v
Vijayan Krishnan
11/22/2021, 11:40 AMdo you have dont_touch variable in your lib for those manually inserted cells?
d
Dinesh A
11/22/2021, 11:43 AMThis will not a .lib attributes & These are not special cells .. This is constraint to tool to avoid modifying specific instances
Dinesh A
11/22/2021, 11:44 AMMy analysis says the changes is happening in : src/rsz/src/Resizer.cc
Resizer::resizeToTargetSlew(const Pin *drvr_pin,
bool update_count)
{
Instance *inst = network_->instance(drvr_pin);
LibertyCell *cell = network_->libertyCell(inst);
if (cell) {
bool revisiting_inst = false;
if (hasMultipleOutputs(inst)) {
revisiting_inst = resized_multi_output_insts_.hasKey(inst);
debugPrint(logger_, RSZ, "resize", 2, "multiple outputs{}",
revisiting_inst ? " - revisit" : "");
resized_multi_output_insts_.insert(inst);
}
ensureWireParasitic(drvr_pin);
// Includes net parasitic capacitance.
float load_cap = graph_delay_calc_->loadCap(drvr_pin, tgt_slew_dcalc_ap_);
if (load_cap > 0.0) {
LibertyCell *target_cell = findTargetCell(cell, load_cap, revisiting_inst);
if (target_cell != cell) {
debugPrint(logger_, RSZ, "resize", 2, "{} {} -> {}",
sdc_network_->pathName(drvr_pin),
cell->name(),
target_cell->name());
if (replaceCell(inst, target_cell, true)
&& !revisiting_inst
&& update_count)
resize_count_++;
}
}
}
return false;
}
Currently i am locally hacking this logic
Dinesh A
11/22/2021, 11:45 AMI see this logic blindly changes any cells load cap > 0.0 with higher drive equivalent cells.
v
Vijayan Krishnan
11/22/2021, 12:04 PMok.. wait for update from @User
a
Austin Rovinski
12/21/2021, 1:57 AMSorry I don't check this slack often. Technically ODB supports this (setting with
setDoNotTouch()isDoNotTouch()FIXEDdoNotTouchAustin Rovinski
12/21/2021, 1:58 AMA temporary hack is that I know resizer ignores special nets. So if you mark that net as special then it will ignore the net as well as any instances attached to it. But this may yield undesirable results.
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