MDK-ARM Keil, MDK-ARM Datasheet - Page 45

• Manufacturer Part Number: MDK-ARM
• Description: KIT REALVIEW MCU DEVELOPMENT
• Manufacturer: Keil
• Type: Compiler and IDEr

Specifications of MDK-ARM

• For Use With/related Products: ARM MCUs
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Getting Started: Building Applications with RL-ARM
System Timer Configuration
The system timer configuration section defines which on-chip timer will be used
to generate a periodic interrupt to provide a time base for the scheduler. On
ARM7 and ARM9-based microcontroller, you need to make use of a general-
purpose timer available in the silicon. With a Cortex-based microcontroller,
there is no need to select a timer, as the Cortex processor contains a dedicated
SysTick timer, which is intended to be used by an RTOS. In both cases, we must
next define the input frequency to the timer. For an ARM7 or ARM9-based
microcontroller this will generally be the advanced peripheral bus frequency. For
a Cortex-MX-based microcontroller it will generally be the CPU frequency.
Next, we must define our timer tick rate. Timer interrupts are generated at this
rate. On each timer tick, the RTOS kernel will check for RTOS features
(scheduler, events, semaphores, etc) and then schedule the appropriate action.
Thus, a high tick rate makes the RTOS more sensitive to events, at the expense of
continually interrupting the executing task. The timer tick value will depend on
your application, but the default starting value is set to 10ms.
Round Robin Task Switching
The final configuration setting allows you to enable round robin scheduling and
define the time slice period. This is a multiple of the timer tick rate, so in the
above example, each task will run for five ticks or 50ms before it will pass
execution to another task of the same priority that is ready to run. If no task of
the same priority is ready to run, it will continue execution.
Scheduling Options
RTX allows you to build an application with three different kernel-scheduling
options. These are:
Pre-emptive scheduling,
Round robin scheduling, and
Co-operative multi-tasking.
45