Power Management in SDR Max Robert Jeffrey H

Power Management in SDR Max Robert, Jeffrey H. Reed Mobile and Portable Radio Research Group (MPRG) Virginia Tech September 14, 2004 1

Overview Power fundamentals ¡ Overview of approaches ¡ Current state of technology ¡ Power management for SDR ¡ l l ¡ Operation states Interface descriptions Conclusion 2

Power Basics ¡ Terms: l l ¡ Fixed attributes l l ¡ α: switching activity C: capacitance V: voltage f: operating frequency Switching activity (algorithm-specific) C is fixed Attributes open to modification l V, f 3

Software-controlled power ¡ Some attributes are determined at design time and cannot be changed at run-time l l ¡ Compiler optimizations Waveform design Attributes that can change at runtime l l Operating voltage Operating frequency Timing control ¡ Thread management in the case of processors Active components 4

General Power Management ¡ Power management split into three principal categories l Previous work on each section varies in depth 5

Software-Controlled Attributes ¡ Timing management l l Thread priority in the case of a GPP or (sometimes) DSP Bus/message management in system ¡ ¡ Algorithm may optimize wait times to cluster work for component Voltage and Frequency selection are related l Higher voltage will allow higher frequencies ¡ Optimal voltage for frequency not necessarily the best choice l l Active component selection is a subset ¡ ¡ Voltage switching may be slower than frequency switching ¡ May desire to maintain operating range for quick response Set voltage or frequency to zero for that component Flexible RF l Still unclear what attributes of the RF will be software-controlled ¡ l Mixer bias, filter BW, others Framework- and application-based strategies need to be sufficiently flexible to allow smooth integration of flexible RF control 6

Application & Hardware ¡ Significant previous research l l ¡ Adaptive management algorithms Advanced power hardware-level power management techniques Application- and HW-based strategies well suited for static applications l Current way of developing power-saving strategies ¡ Fixed waveform l Can be optimized to specific platform 7

Operating System/Environment ¡ Software structure necessary to support power management functionality l Standard interface ¡ Switch between different states l ¡ l i. e. : sleep (several levels), active States not necessarily limited to sleep modes Standard management structure ¡ Maintain state of all devices in system l ¡ State machine for describing system Unified structure for handling associated devices 8

State-of-the-Art ¡ Development limited to PC needs l ¡ BIOS-based management l ¡ Power management for laptops ¡ Sleep mode management BPM (BIOS power management) ¡ Has no awareness of the user’s (or application’s) needs Operating-system based management l l OSPM (OS power management) Current de-facto standard ¡ Most publications today are algorithms for the efficient switching between states using OSPM 9

ACPI ¡ Advanced Configuration and Power Interface l State machine used to describe machine configuration ¡ l States associated with different parts of the system Common interface provided to enact changes in the state of the system 10

ACPI States ¡ Basic set of states l Cx ¡ l CPU states Dx ¡ States for peripheral device l l Modem Network card Screen Hard drive 11

Interface Descriptions ¡ Multiple standardized interfaces provided l Example Acpi. Enter. Sleep. State. Prep ¡ Acpi. Enter. Sleep. State ¡ Acpi. Leave. Sleep. State ¡ ¡ Provides common interface for the change of states for the system 12

OSPM ¡ Operating System Power Management l Model describing partitioning of power consumption management Operating system determines when to trigger power management features ¡ BIOS determines how to perform power management features ¡ 13

OSPM/ACPI ¡ OSPM and ACPI integrated l l OSPM provides mechanism for selection of mode ¡ Kernel initiates action ACPI provides common interface to hardware 14

Power Management For SDR ¡ SDR places challenges different from classic communications system l l Can support application swapping Needs to support wide set of devices ¡ Variety of needs and states l ¡ Difficult to narrow to small, well-defined set of states Requires sophisticated power control structures l Applications can be more predicable than PC ¡ Possible to determine “fast enough” speed l Blind throttle for the application may not be enough 15

State Support ¡ ACPI supports mesh state machine l Assumes basic device states can be throttled l Linear transitions (throttle) are a subset of the mesh state machine 16

Problems with Mesh SM ¡ Assumes that all transitions are fundamentally “equal” l ¡ Does not take into account Qo. S issues related with state change Example: l Voltage and frequency are fundamentally linked ¡ Increased voltage will allow a higher set of frequency settings to be supported l Throttle transitions based on the assumption that lowest possible voltage is supported for the desired frequency ¡ If a change in voltage incurs a higher time delay than a change in frequency, could lead to unplanned additional latencies 17

Rate-Change Support in Communications ¡ Example (802. 11 b): l Support alternate processing speeds for different sections of received frame l Benefits ¡ ¡ Minimizes required computing power Provides ability to discard frame before high-speed processing is necessary 18

Rate Change and SDR ¡ Waveform takes place of “user” in SDR l Latencies associated with change of state need to be taken into account ¡ State switching needs to be in order of microseconds Millisecond-level switches may be too slow for some waveforms Ideally, should cluster state changes into transition state l ¡ ¡ Example: l Crusoe TM 5400 automatically controls voltage and frequency settings ¡ ¡ ¡ l Slow ramp in voltage for up-frequency changes followed by fast frequency change Fast down frequency change followed by slow voltage change Changes performed automatically l Possible for some equipment to leave change requests up to the application Voltage regulator can have a significant impact on the transition speeds in core operating voltage ¡ May be too slow (ms+) for some waveforms 19

State Machine Description ¡ Break down state machine into slowchange states and related fast-change states l Provides application with ability to change states quickly during waveform operation ¡ Also supports sleep or standby operation 20

Sample Operation ¡ Fast operation l Can cycle between 500 and 700 MHz ¡ 500 MHz may be more efficient at 1. 5 V l ¡ Can still transition to lower powers l ¡ May choose not to transition, since change to 600 or 700 MHz expected soon Support significantly lower power consumption levels Same concept can apply to other devices l FPGAs, ASICs, CCMs, DSPs 21

Common Interface ¡ Design of common interface will have to wait until conceptual framework is finalized l Will rely on ACPI to determine appropriate interfaces ¡ Will also rely heavily on SCA 3. 0 interface specifications l l SCA 3. 0 concentrates on non-CORBA interface descriptions Challenging task ¡ Generic nature of hardware makes static definition of interfaces unlikely l Will most likely require a generic structure ¡ May be able to leverage AML 22

Application-Level Power Management ¡ Algorithm development l Field of research currently has large number of contributions ¡ Primarily concentrating on PC-based systems l l ACPI/OSPM Clear from OEPM that SDR will have some unique characteristics ¡ Optimization strategies will be based on the permutations possible by conceptual framework l This research venue cannot proceed until conceptual framework is complete 23

Conclusion ¡ Some concepts in power management are fairly mature l l l ¡ Current state-of-the-art does not cover all needs of SDR l ¡ PC power management Voltage and frequency scaling Policies and algorithms Unique issues related to nature of SDR Actively developing techniques to resolve these issues 24

Acknowledgement ¡ This work is funded by the DCI Postdoctoral Research Fellowship and the MPRG Affiliates Program 25