vyges-buffer-insert

STA-driven buffer insertion: a gate-level netlist in, a buffered netlist out — buffers added where a driver's output transition is too slow, scored by a real static-timing engine.

Vyges open EDA tools. The third of the "close-timing" engines, after vyges-resize (drive strength) and vyges-vt-swap (threshold voltage). Those swap a cell for one with the same footprint; this one adds cells. When a net is so heavily loaded that its driver's transition (slew) blows past the limit, vyges-buffer-insert splits the net: a fresh buffer takes over a share of the sinks, so the original driver sees less load and switches faster.

What it does

vyges-buffer-insert finds the driver whose output transition most exceeds a max_slew limit, splits its net (the buffer drives half the sinks; the driver keeps the rest), rebuilds the timer on the mutated netlist, and keeps the insertion if the worst transition dropped without breaking setup. It repeats until every net is under the limit or the effort budget is spent.

  netlist + .lib + constraints ──[ vyges-buffer-insert ]──►  buffered netlist  (+ before/after slew & timing)

Each candidate is scored by the vyges-sta-si timer — it's pure Rust, so you can experiment with GPUs too via rust-gpu. Because inserting a buffer changes the netlist topology (unlike resize/vt-swap, which only swap a cell), each candidate is a fresh timing build — correct, and bounded by the effort budget. It is a pre-place structural fixup: it decides where in the logical net to split and hands placement of the new buffer back to the flow.

The job

A .bufins file is a superset of a .sta timing job, plus the insertion knobs:

design:     top
netlist:    top.v
lib:        tt.lib
spef:       top.spef          # optional — score against real interconnect (post-place)
clock:      clk 1.2
input_slew: 0.02
output_load: 0.01
buffer:     BUF_X2            # the buffer cell to insert (one input, one output)
max_slew:   0.15             # transition limit (ns); drivers above it are relieved
min_fanout: 2                # only split nets with at least this many sinks
effort:     medium           # low | medium | high  (max buffers to insert)
dont_touch: clk_* *scan*     # driver-instance globs to leave alone

Use it

cargo build --release            # std-only (depends on the open vyges-sta-si timer)

vyges-buffer-insert run   top.bufins -o buffered.v       # buffer -> netlist
vyges-buffer-insert run   top.bufins --json              # before/after slew + timing as JSON
vyges-buffer-insert run   top.bufins --fail-on-violation # exit 3 if still violating (CI gate)
vyges-buffer-insert check top.bufins                     # validate the job
vyges-buffer-insert demo                                 # buffer a built-in example (no files)
# common flags: -o FILE · --json · -q/--quiet · -v/--verbose · -h/--help · -V/--version

See examples/fanout.bufins for a runnable example.

Domain coverage

vyges-buffer-insert operates on the standard-cell digital abstraction — it splits over-transition / high-fanout nets in a gate-level netlist by inserting standard-cell buffers, each candidate scored by the digital vyges-sta-si timer. That makes it a digital optimization engine: it applies wherever a design is built from characterized standard cells with buffer cells in the Liberty. It does not apply to analog / mixed-signal blocks — they have no gate-level net topology or standard-cell buffers, and no Liberty-arc analogue for the timer to score. For analog / mixed-signal physical and integrity coverage, reach for the analog-capable Vyges engines — lvs, layout, em-ir, thermal, and extract.

Status & bounds

v0 relieves over-transition nets by load-splitting with the buffer cell you name; it keeps setup met (a buffer costs a little delay, absorbed from slack) and reports worst transition + WNS before and after. The split is a simple halving of the sinks — balanced / recursive / placement-aware splitting and explicit hold-buffering are future work, as is an incremental timing update for the topology change (each candidate currently rebuilds). It is not a place-and-route tool. Sign-off is still the golden timer — vyges-buffer-insert's numbers are a fast, license-free guide.