ARM® Cortex® M4 Cookbook

Estimating microcontroller performance

The millions of instructions that can be executed per second (MIPS) is one measure of processor performance. This figure depends on the processor architecture, the clock speed, the memory performance, and so on. The microcontroller can be clocked from one of three oscillator sources. A high speed external (HSE) clock is derived from a 25 MHz crystal oscillator connected between two pins of the microcontroller. A high speed internal (HSI) clock is sourced from an internal 16 MHz resistor-capacitor (RC) controlled oscillator, and a Phase Locked Loop (PLL) can be configured to provide multiples of either HSE or HSI.

A peripheral called reset and clock control (RCC) allows the clock source to be selected and ...