Power Management in SDR
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Transcript of Power Management in SDR
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Power Management in SDR
Max Robert, Jeffrey H. ReedMobile and Portable Radio Research Group (MPRG)Virginia TechSeptember 14, 2004
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Overview
Power fundamentals Overview of approaches Current state of technology Power management for SDR
Operation states Interface descriptions
Conclusion
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Power Basics
Terms: α: switching activity C: capacitance V: voltage f: operating frequency
Fixed attributes Switching activity (algorithm-specific) C is fixed
Attributes open to modification V, f
2P CV f
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Software-controlled power
Some attributes are determined at design time and cannot be changed at run-time Compiler optimizations Waveform design
Attributes that can change at runtime Operating voltage Operating frequency Timing control
Thread management in the case of processors Active components
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General Power Management Power management split into three principal
categories Previous work on each section varies in depth
H ardw are
O perating System /Environm ent
Application
- Thread priority a lgorithm s- Dynam ic Voltage Scaling (D VS) a lgorithm s- Dynam ic Frequency Scaling (D FS) a lgorithm s- Policy selection a lgorithm s
- Advanced C onfiguration and Pow er In terface (ACPI)- O perating System Pow er M anagem ent (O SPM )
- M ulti-vo ltage H W (C rusoe)- M ulti-frequency H W (C PU s, FPG As, ASIC s)- F lexib le RF- E ffic ient com pilers- A lternate data flows
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Software-Controlled Attributes
Timing management 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
Higher voltage will allow higher frequencies Optimal voltage for frequency not necessarily the best choice
Voltage switching may be slower than frequency switching May desire to maintain operating range for quick response
Active component selection is a subset Set voltage or frequency to zero for that component
Flexible RF Still unclear what attributes of the RF will be software-controlled
Mixer bias, filter BW, others Framework- and application-based strategies need to be sufficiently
flexible to allow smooth integration of flexible RF control
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Application & Hardware
Significant previous research Adaptive management algorithms Advanced power hardware-level power
management techniques Application- and HW-based strategies well
suited for static applications Current way of developing power-saving
strategies Fixed waveform
Can be optimized to specific platform
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Operating System/Environment
Software structure necessary to support power management functionality Standard interface
Switch between different states i.e.: sleep (several levels), active
States not necessarily limited to sleep modes Standard management structure
Maintain state of all devices in system State machine for describing system
Unified structure for handling associated devices
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State-of-the-Art
Development limited to PC needs Power management for laptops
Sleep mode management BIOS-based management
BPM (BIOS power management) Has no awareness of the user’s (or
application’s) needs Operating-system based management
OSPM (OS power management) Current de-facto standard
Most publications today are algorithms for the efficient switching between states using OSPM
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ACPI
Advanced Configuration and Power Interface State machine used to describe
machine configuration States associated with different parts of
the system Common interface provided to enact
changes in the state of the system
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ACPI States Basic set of
states Cx
CPU states Dx
States for peripheral device
Modem Network card Screen Hard drive
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Interface Descriptions
Multiple standardized interfaces provided Example
AcpiEnterSleepStatePrep AcpiEnterSleepState AcpiLeaveSleepState
Provides common interface for the change of states for the system
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OSPM
Operating System Power Management Model describing partitioning of power
consumption management Operating system determines when to
trigger power management features BIOS determines how to perform power
management features
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OSPM/ACPI
OSPM and ACPI integrated OSPM provides
mechanism for selection of mode
Kernel initiates action
ACPI provides common interface to hardware
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Power Management For SDR
SDR places challenges different from classic communications system Can support application swapping Needs to support wide set of devices
Variety of needs and states Difficult to narrow to small, well-defined set of
states Requires sophisticated power control
structures Applications can be more predicable than PC
Possible to determine “fast enough” speed
Blind throttle for the application may not be enough
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State Support
ACPI supports mesh state machine Assumes basic device states can be throttled
Linear transitions (throttle) are a subset of the mesh state machine
S 1 S 2 S n
S 1 S 2 S n
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Problems with Mesh SM
Assumes that all transitions are fundamentally “equal” Does not take into account QoS issues related with
state change Example:
Voltage and frequency are fundamentally linked Increased voltage will allow a higher set of
frequency settings to be supported 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
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Rate-Change Support in Communications
Example (802.11b): Support alternate processing speeds for different
sections of received frame
Benefits Minimizes required computing power Provides ability to discard frame before high-speed
processing is necessary
PLC P Prefix PLC P Payload
1M bps (P ream ble+H eader) 11M bps PSD U
192us typ ically ~400us
Pro
cess
ing
C W
SlowFast
Tra
nsiti
on
Tra
nsiti
on
D ecision po in t: d iscard fram e?
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Rate Change and SDR
Waveform takes place of “user” in SDR 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 Example:
Crusoe TM5400 automatically controls voltage and frequency settings
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
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
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State Machine Description
Break down state machine into slow-change states and related fast-change states Provides application
with ability to change states quickly during waveform operation
Also supports sleep or standby operation
V 3F3,1 F3,2 F3,3
V 1F1,1 F1,2 F1,3
V 2F2,1 F2,2 F2,3
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Sample Operation
Fast operation Can cycle between 500 and
700 MHz 500 MHz may be more
efficient at 1.5V May choose not to
transition, since change to 600 or 700 MHz expected soon
Can still transition to lower powers Support significantly lower
power consumption levels Same concept can apply to
other devices FPGAs, ASICs, CCMs, DSPs
1.2V100 200 300
1.8V500 600 700
1.5V300 400 500
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Common Interface
Design of common interface will have to wait until conceptual framework is finalized Will rely on ACPI to determine appropriate
interfaces Will also rely heavily on SCA 3.0 interface
specifications SCA 3.0 concentrates on non-CORBA interface
descriptions Challenging task
Generic nature of hardware makes static definition of interfaces unlikely
Will most likely require a generic structure May be able to leverage AML
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Application-Level Power Management
Algorithm development Field of research currently has large number of
contributions Primarily concentrating on PC-based systems
ACPI/OSPM Clear from OEPM that SDR will have some
unique characteristics Optimization strategies will be based on the
permutations possible by conceptual framework
This research venue cannot proceed until conceptual framework is complete
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Conclusion
Some concepts in power management are fairly mature PC power management Voltage and frequency scaling Policies and algorithms
Current state-of-the-art does not cover all needs of SDR Unique issues related to nature of SDR
Actively developing techniques to resolve these issues
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Acknowledgement
This work is funded by the DCI Postdoctoral Research Fellowship and the MPRG Affiliates Program