The eCos kernel system clock is implemented using an on-chip Timer. Depending on the device this will either be a Timer Counter, a Simple Timer, or the Periodic Interval Timer. The kind of device used is determined by the platform HAL. 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 selected Timer 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.