"cross" measure

Purpose

Find the time or frequency where a probed value crosses a reference.

cross(probe="p(d)" cross=value begin=time end=time rise fall last first)

arg name	default	description
probe	required	The name of a probe to measure.
cross	0	The value it crosses.
begin after	-infinity	The window begins at this time or frequency.
end before	+infinity	The window ends at this time or frequency.
first	true	Find the first crossing in the window. (Cancels last.)
last	false	Find the last crossing in the window. (Cancels first.)
rise	true	Consider only rising crossings. (Cancels fall.)
fall	false	Consider only falling crossings. (Cancels rise.)

For this function to detect a crossing, it must actually cross.

A steady state at the cross value is not a crossing.
Being at the cross value and leaving is not a crossing.
Merely touching (becoming equal to) the cross value and leaving from the same side is not a crossing.

If there is no crossing within the specified range, it returns “Inf” (infinity).

If you didn't store the waveform (see store command), it throws a “no match” exception, which prints “no match”.

measure t2 = cross(probe="v(out)" cross=0 rise last)

Find the last time that v(out) crosses 0, going up.

measure t1 = cross(probe="v(out)" cross=0 rise last before=t2)

Find the last rising zero crossing before t2.

param period = {t2-t1}
param frequency = {1/period}

Params are interpreted like a functional language so they will be updated whenever t1 or t2 changes.