Nonstop pins are pins that would normally be considered endpoints of the clock tree, but
instead IC Compiler traces through them to find the clock tree endpoints. The clock pins of
sequential cells driving generated clocks are implicit nonstop pins. In addition, IC Compiler
supports user-defined (or explicit) nonstop pins.
To specify a nonstop pin, use the
set_clock_tree_exceptions -non_stop_pins
Exclude pins are clock tree endpoints that are excluded from clock tree timing calculations
and optimizations. IC Compiler uses exclude pins only in calculations and optimizations for
design rule constraints. In addition to the exclude pins inferred by IC Compiler (the implicit
exclude pins), IC Compiler supports user-defined (or explicit) exclude pins. For example, you
might define an exclude pin to exclude all branches of the clock tree that fan out from some
combinational logic or to exclude an implicit stop pin.
During clock tree synthesis, IC Compiler isolates exclude pins (both implicit and explicit) from
the clock tree by inserting a guide buffer before the pin. Beyond the exclude pin, IC Compiler
never performs skew or insertion delay optimization, but does perform design rule fixing.
To specify an exclude pin, use the
set_clock_tree_exceptions -exclude_pins
command.
Float pins are clock pins that have special insertion delay requirements. IC Compiler adds
the float pin delay (positive or negative) to the calculated insertion delay up to this pin.
Stop pins are the endpoints of the clock tree that are used for delay balancing. During clock
tree synthesis, IC Compiler uses stop pins in calculations and optimizations for both design
rule constraints and clock tree timing (skew and insertion delay).
The default clock sinks are implicit stop pins. In addition, IC Compiler supports user-defined
(or explicit) stop pins. For example, you might define a stop pin to end a branch at an input
to a combinational cell or to use an implicit exclude pin as a clock sink.
IC Compiler assigns a phase delay of zero to all stop pins (implicit and explicit) and uses this
delay during delay balancing.
To specify a stop pin, use the
set_clock_tree_exceptions -stop_pins command.
