Getting the Most Out of Low Power MCUs Part I: Low Power MCU Concepts and Capabilities 1/14/2013 Warren Miller

This Week’s Agenda 1/14/13 Low Power MCU Concepts and Capabilities 1/15/13 Low Power Modes in Detail 1/16/13 Low Power Peripherals 1/17/13 Extending Battery Lifetime 1/18/13 Advanced Example Designs

This Week’s Agenda 1/14/13 Low Power MCU Concepts and Capabilities 1/15/13 Low Power Modes in Detail 1/16/13 Low Power Peripherals 1/17/13 Extending Battery Lifetime 1/18/13 Advanced Example Designs

Class Description Modern MCUs have a variety of features that support very low power operation. In order to get the most out of these new devices we will review common concepts Like special low power operating modes and common capabilities Like special peripheral operations that most modern Low Power MCUs share.

Today’s Topics Goals and Objectives Why Low Power? MCU Power- an Overview Power Sources, Voltage Characteristics, Current Characteristics Processing Efficiency MCU Architecture- an Overview Processor Memory Peripherals Common Low Power MCU Capabilities Low Frequency Operation, Low Operating Voltage Low Power Modes, Low Power Peripherals

Goals and Objectives Understand, at the overview level, key concepts we will use in the rest of the class Power Sources Main MCU elements and any special low power characteristics (CPU, Memory and Peripherals) Low Frequency Operation Low Voltage Operation Low Power Modes

Why Low Power? More than $9B in products using rechargeable batteries used in homes, retail and warehouses Battery powered electronics use over $30B in electricity annually 5-10% of residential electricity cost comes from standby power (equipment on, but not doing anything)

MCU Power- An Overview Power Sources: Battery Energy Harvesting Size, mAh, Self Discharge, Lifetime Energy Harvesting Solar, Thermal, Pressure, Magnetic, etc Super Cap Voltage, Charge (Current over time) System Power Why would low power be important? Mains 200mAh 2000mAh

MCU Power- An Overview Voltage and Current Characteristics Voltage Range Wide range of VCC for battery operation Internal regulator to generate core voltage Voltage vs Frequency Higher frequency of operation requires higher voltage, PLL, Clock Osc, Flash Memory, Logic Static Current The amount of current required when nothing is switching Dynamic Current When signals switch state, current flow is required

MCU Active Characteristics MCU Efficiency Metrics (DMIPS-based) MCU Power- An Overview Processing Efficiency Max Clock Rate Instruction Cycle Time Wait States mA mA/DMIP Other Considerations Power Consumption MCU #1 MCU #2 MCU #3 MCU Active Characteristics MHz 100 168 mA 35 87 66 mA/MHz 0.35 0.52 0.66 MCU Efficiency Metrics (DMIPS-based) DMIPS 165 125 mA/DMIPs 0.21 0.70 0.53 DMIPS = Drystone MIPS, a benchmark for integer based processing. A mix of common processing functions used to compare various computer architectures. 20 years old so it is still useful but should not be considered the only metric needed. Pun on Whetstone which included Floating Point operations. Note: DE Vax 11/780 is considered a 1 MIPS machine with 1757 Drystones per second. DMIPS can result in better measures for CISC architectures vs RISC architectures if the CISC machine can process DMIPS functions in fewer instructions…

MCU Architecture- CPU CPU Blocks Program Counter Instruction Register Control Unit Register File ALU Status Register Stack Pointer Some Low Power Points: Data Processing Width, Number of Working Registers vs State Save Time and Active Power Requirements

MCU Architecture- CPU Control Inst #1 Inst #2 Inst #3 Inst #4 Fetch Decode Execute Pipelined Execution Fetch, Decode, Execute Sequential Operations Pipeline Stall Intelligent Control- Low Power Disable Decode Blocks Separate Execution Units Gated Clocks

MCU Architecture- Memory Low Power Features Code Memory: Flash Fetch size Wait states Cache Data Memory: SRAM Volatile Battery back-up Execute program from RAM

MCU Architecture- Memory Low Power Features Data Flash Non-volatile Key Configuration Data Saved Operating Data Resets or Brown-out Tamper Protection Time Stamps Power Failure Data

MCU Architecture- Peripherals GPIO GP Timer Low Power Features Bus Interface Peripheral Functions GPIOs Serial Standards Independent Operation GP Timers Watchdog Timers Interrupts DMA Interrupt DMA Serial CPU Debug Mult Div MAC Clock Watch Dog

MCU Architecture- Peripherals Low Power Features Clock Frequency Requirements, Analog to Digital Conversion Battery Back-up, Low Voltage Detection

MCU Low Modes- Overview Run: CPU, Clock, Peripherals: Running Sleep, Wait: CPU Clk Gated; Clock, Peripherals: Running Stop: CPU, Some Peripherals, Some Clocks: Gated Standby, Hibernate: CPU, Clock: Off; Some Peripherals: External Clock Other Blocks Flash, SRAM, Regulator, PLL, Osc, etc. RTC, WDT, Brownout Detect, etc. Additions Very Low Power, Deep, Snooze, etc. Different names for similar functions. You need to read the detailed descriptions in suppliers datasheets. Much more in next class.

Specialized Low Power Peripherals Low Power Oscillators Low Power Interval Timers Low Power Watchdog Timers Battery Back-up Operation Input Detection Low Power UART Etc.

Additional Resources WE Energy Harvesting Brochure: http://tinyurl.com/bb6m9nh MicroChip XLP Technology: http://tinyurl.com/bxq6lmd STMicroelectronics STM32L: http://tinyurl.com/9fpjhme Energy Micro MCUs: http://tinyurl.com/b9hnsbw TI MSP430 MCUs: http://tinyurl.com/7qqtpfa Renesas RL78 MCUs: http://tinyurl.com/aczhpmr Renesas RL78 Eval Kit: http://tinyurl.com/cbrnmdl http://ww1.microchip.com/downloads/en/devicedoc/01146b_chapter%202.pdf

This Week’s Agenda Tomorrow 1/14/13 Low Power MCU Concepts and Capabilities 1/15/13 Low Power Modes in Detail 1/16/13 Low Power Peripherals 1/17/13 Extending Battery Lifetime 1/18/13 Advanced Example Designs