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November 29, 2012November 29, 2012 by Jean-Luc Aufranc (CNXSoft) - No Comments

SoC Power Measurement with ARM Energy Probes and Linux EAP Tools

Andy Green, TI Landing Team lead at Linaro, gave an interesting presentation entitled “How to measure SoC power” at Linaro Connect Europe 2012. This talk was specifically aimed at software engineers, so that they know how to properly measure power consumption, and take actions to optimize the software to decrease it. In the first part of the presentation, he gives an overview of electronics basics with definition of voltage, load, current and power, units used for power measurements (Clue: you need to use Watts), and how voltage, current and power can be measured with voltmeters and ammeters. When you want to measure power in a rail, you would usually insert a shun resistor, use a multimeter and derive the power from the resistance and the measured voltage (P=V2/R). He also gives details about regulator efficiency, choosing measurement sampling… There are 4 common measurements strategies: DC IN – Easiest way, gives the complete […]

February 27, 2012 by Jean-Luc Aufranc (CNXSoft) - No Comments

Comparing Power Saving Techniques For Multicore ARM Platforms – ELC 2012

Vincent Guittot, ST Ericsson and Linaro, compares power saving techniques for multicore ARM plaforms at Embedded Linux Conference 2012. Abstract: CPU hotplug is used on ARM platform as a power management feature for aggressive low power use cases. It has not been initially designed for that purpose, which implies some constraints on its use but the same power consumption level can’t be reached with the scheduler load balance and/or additional features like cpuset up to now. This presentation will discuss how CPU hotplug matches the low power use case requirements and how we can get closer to this behavior with sched_mc. Then we will also show what prevents the scheduler to reach the same power consumption level as CPU hotplug and how we can solve some of these issues. This presentation is aimed at anybody who is interested to understand why ARM platforms still use CPU hotplug and what should […]

November 1, 2010July 17, 2012 by Jean-Luc Aufranc (CNXSoft) - No Comments

Accurate Time Keeping in Embedded Systems

In many embedded systems, there is a need to keep accurate time/date. This is often performed using an RTC (Real-Time Clock). However, uncalibrated RTC are not that accurate. For example, ST Microelectronics M41T94 RTC datasheet explains that: Uncalibrated clock accuracy will not exceed ±35 ppm (parts per million) oscillator frequency error at 25°C, which equates to about ±1.53 minutes per month. . In order to improve the accuracy, you’ll need to calibrate the crystal for each board at the factory using a frequency counter, that will greatly improve accuracy, for M41T94: When the Calibration circuit is properly employed, accuracy improves to better than ±2 ppm at 25°C. However, calibrating the crystal will further increase the manufacturing costs. Another way to have a very accurate time keeping, is to use the power supply frequency (50 Hz/60 Hz) which is extremely accurate due to interoperability requirements between electricity providers. In the diagram […]