The timer divisor calculations in this driver are over complicated.
There are three timers on the board. They all use the same base clock
with a fixed prescaler for each timer. The base clock used depends on
the board version and type:
APCI-3120 Rev A boards OSC = 14.29MHz base clock (~70ns)
APCI-3120 Rev B boards OSC = 20MHz base clock (50ns)
APCI-3001 boards OSC = 20MHz base clock (50ns)