rtel wrote on Sunday, April 10, 2005:

Nowadays I study FreeRtos operating system,but I can’t understand “kernel tick” issue. what is a tick? I downloaded a ebook which is called “Real-Time Concepts for Embedded  Systems” but I couldn’t find anything about “ticks”. Please explain me that concept.

rtel wrote on Sunday, April 10, 2005:

[This was an email support request which I have copied to this forum.]

The RTOS tick is a fixed interval periodic interrupt generated form a hardware timer.  It is used to measure real time.   The resolution of time that can be measured is dependent on the tick period.

For example, if the RTOS tick frequency is set to 1ms then time can be measured with an accuracy of 1ms  but there is also an overhead of having an interrupt every 1ms.  If this resolution is not necessary (it usually isnt) then the overhead can be reduced by slowing down the tick frequency to say 10 or even 100ms.

The tick interrupt is also used for round robin scheduling.  When there is more than one task that have the same priority and are ready to run, then the tick interrupt is used to switch between the tasks.