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July 17, 2002
48
Processor Power Supplies and Power
Management
LongRun Power Management
LongRun power management is a power saving feature of TM5500/TM5800 processors that allows the
processor to dynamically change its operating frequency and voltage in response to the instantaneous
performance demands of running applications. The basic goal is to provide just-sufficient performance for the
task at hand, without expending any more energy than is strictly necessary.
In Code Morphing software, LongRun power management defines up to eight
performance levels
, each
consisting of a unique operating frequency and a unique operating voltage. Each successive performance
level has a higher frequency and voltage than the previous one. When LongRun power management is
enabled, it will raise and lower the performance level based on the amount of idle time in the system.
The algorithms that LongRun power management uses to determine when to raise or lower the performance
level are fairly complex, and beyond the scope of this document. This document will only focus on how
LongRun power management relates to hardware signals external to the processor.
Frequency Change Mechanism
When the core and memory frequencies are changed, LongRun power management must start by ensuring
that there is no external activity in the system during the frequency change. This is accomplished by flushing
any queued PCI or memory writes, and force-granting the PCI bus to the processor.
In addition, since the memory frequencies may be changed at the same time as the core frequency, the
memories must not be accessed during the frequency change process. LongRun power management thus
places the memories into self-refresh, and then writes new multipliers/divisors for the core and memory
frequencies. Then the clocks are stopped, and hardware commences the frequency change, after which the
processor wakes up and starts running with the new core and memory frequencies.
Finally, the memories are brought out of self-refresh, and the force-granted PCI bus is released.
Latency
Timing
Information/Requirements
Diagram Note
ISR execution to PCI Force Grant
1 µS typical
2 µS maximum
T1
PCI Force Grant to memories in self-refresh
1 µS typical
2 µS maximum
T2
Memory self-refresh to clocks off
1 µS typical
2 µS maximum
T3
PLL relock time
10 µS minimum required
value configurable
T4
Clocks on to memory out of self-refresh
1 µS typical
2 µS maximum
T5
Memory out of self-refresh to PCI Force Grant
deassert
1 µS typical
2 µS maximum
T6
PCI Force Grant deassert to end of ISR execution
2 µS typical
4 µS maximum
T7
Voltage regulator settling time
64 µS default
value configurable
1
1.
This value may be required to be set to 256 µS for some silicon revisions
T8
Содержание Crusoe TM5500
Страница 1: ...TM5500 TM5800 System Design Guide July 17 2002...
Страница 6: ...July 17 2002 6 List of Tables...
Страница 8: ...July 17 2002 8 List of Figures...
Страница 50: ...July 17 2002 50 Processor Power Supplies and Power Management...
Страница 110: ...July 17 2002 110 System Design Considerations...
Страница 122: ...July 17 2002 122 System Design Checklists...
Страница 128: ...July 17 2002 128 Serial Write protection PLD Data...
Страница 130: ...July 17 2002 130 Index...