STMicroelectronics AN3129 Real-time Performance Using FIQ Interrupt Handling in SPEAr MPUs Application Note

About this manual

This document provides software developers with information on utilizing the Fast Interrupt Request (FIQ) mechanism within the Linux kernel on the SPEAr family of embedded MPUs. It details the interrupt logic, hardware mechanisms, and software requirements necessary to implement FIQ handlers effectively.

The note covers the specific limitations of using FIQs in a Linux environment, such as restrictions on API usage and memory access. Furthermore, it describes a latency measurement module included in the STLinux SPEAr BSP release kernel code, which allows developers to measure IRQ and FIQ handling latencies.

What's inside

• Introduction
• SPEAr interrupt logic
• Linux kernel IRQ handling latency
• FIQ handler environment
• IRQ latency measurement
• Module internals
• Performance measurements

Frequently asked questions

What is the maximum range of interrupt latency measured by the module?

The frequency counter captures a range from 0 to 9600 ticks, which corresponds to 0 to 200 microseconds.

What CPU speed was used in the performance measurements?

The ARM core running at 333 MHz was used for the performance measurements.