The eCos kernel system clock is implemented using the Periodic Interval Timer (PIT). By default, the system clock interrupts once every 10ms, corresponding to a 100Hz clock. This can be changed by the configuration option CYGNUM_HAL_RTC_DENOMINATOR which corresponds to the clock frequency. Other clock-related settings are recalculated automatically if the denominator is changed. If the desired frequency cannot be expressed accurately solely with changes to CYGNUM_HAL_RTC_DENOMINATOR, then the configuration option CYGNUM_HAL_RTC_NUMERATOR may also be adjusted, and again clock-related settings will automatically be recalculated.
The PIT is also used to implement the HAL microsecond delay function,
HAL_DELAY_US. This is used by some device
drivers, and in non-kernel configurations such as with RedBoot where
this timer is needed for loading program images via X/Y-modem
protocols and debugging via TCP/IP. Standalone applications which
require RedBoot services, such as debugging, should avoid use of this
timer.