F_CPU = ### INSERT PRESCALED SYSTEM CLOCK SPEED HERE, IN HZ ###\r
\r
\r
-# Input clock frequency.\r
+# USB controller master clock frequency.\r
# This will define a symbol, F_USB, in all source code files equal to the\r
# input clock frequency (before any prescaling is performed) in Hz. This value may\r
# differ from F_CPU, as the USB clock is often sourced from the same oscillator as\r