your code is incomplete, but is something like this:

- do you have a signal with an undetermined width
- that signal is connected to INT0
- as long the signal at INT0 is high, TL0 counts the machine cycles

you know your clock, you have the pulse counting, do the math.

eg. 200 machine cycles, so the width is 200 x 1us (for a 12MHz crystal) = 200us

HTH

orlando