ARM processors support various performance monitoring registers, the most basic being a cycle count register. This is how to make use of it on the Raspberry Pi 3 with its ARM Cortex-A53 processor. The A53 implements the ARMv8 architecture which can operate in both 64- and 32-bit modes, the Pi 3 uses the 32-bit AArch32 mode, which is more or less backwards compatible with the ARMv7-A architecture, as implemented for example by the Cortex-A7 (used in the early Pi 2’s) and Cortex-A8. I hope I’ve got that right, all these names are confusing
The performance counters are made available through certain coprocessor registers and the mrc and mcr instructions. By default, use of these instructions is only possible in “privileged” mode, ie. from the kernel, so the first thing we need to do is to enable register access from userspace. This can be done through a simple kernel module that can also set up the cycle counter parameters needed (we could do this from userspace after the kernel module has enabled access, but it’s simpler to do everything at once).
Each Friday is PiDay here at Adafruit! Be sure to check out our posts, tutorials and new Raspberry Pi related products. Adafruit has the largest and best selection of Raspberry Pi accessories and all the code & tutorials to get you up and running in no time!
Adafruit publishes a wide range of writing and video content, including interviews and reporting on the maker market and the wider technology world. Our standards page is intended as a guide to best practices that Adafruit uses, as well as an outline of the ethical standards Adafruit aspires to. While Adafruit is not an independent journalistic institution, Adafruit strives to be a fair, informative, and positive voice within the community – check it out here: adafruit.com/editorialstandards
Stop breadboarding and soldering – start making immediately! Adafruit’s Circuit Playground is jam-packed with LEDs, sensors, buttons, alligator clip pads and more. Build projects with Circuit Playground in a few minutes with the drag-and-drop MakeCode programming site, learn computer science using the CS Discoveries class on code.org, jump into CircuitPython to learn Python and hardware together, TinyGO, or even use the Arduino IDE. Circuit Playground Express is the newest and best Circuit Playground board, with support for CircuitPython, MakeCode, and Arduino. It has a powerful processor, 10 NeoPixels, mini speaker, InfraRed receive and transmit, two buttons, a switch, 14 alligator clip pads, and lots of sensors: capacitive touch, IR proximity, temperature, light, motion and sound. A whole wide world of electronics and coding is waiting for you, and it fits in the palm of your hand.
Have an amazing project to share? The Electronics Show and Tell is every Wednesday at 7pm ET! To join, head over to YouTube and check out the show’s live chat – we’ll post the link there.