Performance

The real time performance of an operating system is usually measured using the following parameters.

Interrupt latency
The time it takes from a device asserting an interrupt line until the system dispatching the corresponding interrupt handler (ISR) is the interrupt latency. This includes interrupt-blocking time during which the kernel is pending to respond to an interrupt, saving the tasks context, determining the interrupt source, and invoking the interrupt handler.

Average interrupt latency for NanoOS measured on a 200MHz ARM926EJ-S platform is 1 microsecond#.

Context switch latency
This term defines the time it takes to schedule a task in response to an event that makes it run-able. It involves processing the event/interrupt, the scheduler determining which task to run, saving the current task context and restoring the new one.

The following figure shows the processing involved in a context switch –

Average context switch latency for RoS-ES^TM OS measured on a 200MHz ARM926EJ-S platform is 3.8 microseconds##.

Footprint
Atypical configuration of ISA under ARM platform would have a footprint of 19KB*.

#Measured externally on a 200MHz ARM926EJ-S platform, using continuous external interrupts on the GPIO interface, when the system is lightly loaded

##Measured externally on a 200MHz ARM926EJ-S platform using the GPIO interface when the system is lightly loaded

* on ARM926EJ-S with ARMv5E instruction set