Royal Institute of Technology Voltage and frequency scaling in an embedded microprocessor to enable the implementation of dynamic voltage and frequency scheduling for power management. Master of Science Thesis Jonas Höglund December 13, 2009 Supervisors: Magnus Persson, KTH Barbro Claesson, ENEA Detlef Scholle, ENEA Examiner : Martin Törngren, KTH Master of Science Thesis MMK 2009:98 MDA 358 KTH Industrial Engineering and Management Machine Design SE-100 44 STOCKHOLM Examensarbete MMK 2009:98 MDA 358 Frekvens och spänningsskalning i en inbyggd mikroprocessor; för att möjliggöra implementationen av schemaläggning med stöd för dynamisk frekvens- och spänningsreglering för energihantering. Jonas Höglund Godkänt Examinator Handledare 2009-12-17 Martin Törngren Magnus Persson Uppdragsgivare Kontaktperson Enea AB Detlef Scholle Barbro Claesson Sammanfattning Att minimera energiförbrukning är en mycket viktig del av många utvecklingsprojekt av inbyggda system. Utmaningen består av att minimera systemets energiförbrukning samtidigt som det förväntas leverera en kvalitativ användarupplevelse. Den huvudsakliga metoden som används för att minimera energiförbrukningen en mikroprocessor under programexekvering är att reducera dess klockfrekvens och matningsspänning. För att möjliggöra implementationen av realtidsschemaläggning med stöd för dynamisk justering av processorns spänning och frekvens genomförs en utförlig studie av en Freescale i.MX31- mikroprocessor. Undersökningen fokuserar på relationen mellan energiförbrukning och spännings- och frekvensinställningar. För att möjliggöra frekvens- och spänningsskalning i realtidssammanhang utförs dessutom en tidsanalys av föreslagna spännings- och frekvensjusteringsmetoder och deras lämplighet för användning i realtidssystem utvärderas. För att integrera spännings- och frekvensskalning i OSE RTOS har en mjukvarumodul för operativsystemet utvecklats. Modulen gör det möjligt för OSE-processer att begära spännings- och frekvensändringar genom ett signalinterface. Modulen testas för robusthet och dess korrekta funktion tillsammans med en realtidsschemaläggare med stöd för dynamisk frekvens- och spänningsskalning utvecklad hos Enea verifieras. Slutligen så utvärderas energiförbrukningen av ett testprogram som exekveras av det integrerade systemet. 2 Master of Science Thesis MMK 2009:98 MDA 358 Voltage and frequency scaling in an embedded microprocessor; to enable the implementation of dynamic voltage and frequency scheduling for power management. Jonas Höglund Approved Examiner Supervisor 2009-12-17 Martin Törngren Magnus Persson Commissioner Contact person Enea AB Detlef Scholle Barbro Claesson Abstract Minimizing power consumption is a critical part of many embedded design projects. The challenge is to limit the power consumption of the system and at the same time provide satisfactory service to the user. With regards to microprocessors, the main way of limiting power consumption during program execution is to adjust the frequency and the voltage at which the processor operates. To enable the implementation of real-time scheduling with support for dynamic voltage and frequency scaling, an exhaustive study of the Freescale i.MX31 embedded microprocessor is performed. Specifically, the power consumption relationship to all relevant frequency and voltage settings is investigated. In addition, to enable frequency and voltage scaling in a real-time environment, a complete timing analysis of proposed voltage and frequency scaling methods is performed and their suitability for use in real-time systems is evaluated. To integrate voltage and frequency scaling capability into OSE RTOS, a software module has been developed for this operating system. The module enables OSE processes to request voltage and frequency changes using a signaling interface. The module has been tested for robustness and its correct operation together with a real-time dynamic voltage frequency scheduler developed at Enea has been verified. Finally, an evaluation of the power consumption of a test program running on the integrated system is performed. 3 Contents Contents.......................................................................................................................................................... 4 List of figures ................................................................................................................................................. 5 1 Introduction........................................................................................................................................... 6 1.1 Background ................................................................................................................................. 6 1.2 Problem Statement ...................................................................................................................... 6 1.3 Method ........................................................................................................................................ 7 1.4 Delimitations............................................................................................................................... 7 2 Power management in mobile devices.................................................................................................. 8 2.1 Battery technology and the need for power efficiency................................................................ 8 2.2 The CPU as a consumer of energy .............................................................................................. 8 2.3 The computational needs of mobile handhelds ........................................................................... 9 2.4 Summary ................................................................................................................................... 10 3 Addressing timing requirements of computing systems ..................................................................... 11 3.1 Real-time systems...................................................................................................................... 11 3.2 Worst case execution time......................................................................................................... 14 3.3 Summary ................................................................................................................................... 15 4 Power management techniques for real-time systems ........................................................................ 16 4.1 Sources of power consumption ................................................................................................. 16 4.2 Dynamic Voltage Frequency Scaling........................................................................................ 16 4.3 Summary ................................................................................................................................... 17 5 Hardware support for power management.......................................................................................... 18 5.1 i.MX31 support for frequency scaling....................................................................................... 19 5.2 i.MX31 support for automatic DVFS........................................................................................ 22 5.3 MC13783 support for voltage scaling ....................................................................................... 24 5.4 i.MX31 Frequency/Voltage operating ranges............................................................................ 25 5.5 Summary ................................................................................................................................... 26 6 Supporting software platforms............................................................................................................ 27 6.1 U-boot 1.3.3............................................................................................................................... 27 6.2 OSE 5.4 ..................................................................................................................................... 27 6.3 OSE Bios interface.................................................................................................................... 28 6.4 Summary ................................................................................................................................... 29 7 Design description .............................................................................................................................. 30 7.1 Voltage scaling.......................................................................................................................... 30 7.2 Frequency scaling...................................................................................................................... 31 8 Test suite............................................................................................................................................. 33 8.1 Test cases................................................................................................................................... 33 9 Results................................................................................................................................................. 36 9.1 Determination of CPU power consumption and timing characteristics..................................... 36 9.2 Verification of OSE DVFS module..........................................................................................