MDK-ARM Keil, MDK-ARM Datasheet - Page 31

• 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
31
Task Priority Scheme
When writing an RTOS-based application you must have a clear idea of how you
will prioritize tasks. The FIQ interrupt is the highest priority interrupt on ARM
CPUs (a non-maskable interrupt is available in Cortex processors). The FIQ is
not handled by RTX and so there is no overhead in serving it.
The remaining interrupts are handled as IRQ interrupts, which can be used to
trigger tasks (as discussed above). After the IRQ interrupts, important
background tasks may be assigned an appropriate priority level. Finally, the
round robin tasks can be assigned priority level one with the idle task running at
priority zero.
A typical RTOS priority scheme
places the FIQ and IRQ triggered
tasks at highest priority, followed
by high priority background
tasks, with round robin tasks at
lowest user task priority. The
idle task is at priority zero and
will use up any spare cycles.
Any task that is above the round
robin priority level must be a
self-blocking task, i.e. do a job
and halt. If any high priority task does not block, then it will run forever, halting
any lower priority tasks.