System Clock

The eCos kernel system clock is implemented using the BCM283X System Timer device. By default, the system timer is programmed to interrupt once every 10ms, corresponding to a 100Hz clock. This can be changed with 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. The system timer is clocked at 1MHz, so there are limits on the accuracy of any frequency that is not a factor of 1000000.

The same 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 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.

Timer-based Profiling Support

At present timer based profiling is not supported. This is mainly because the current profiling support is not SMP-aware.