Active State Power Management
Encyclopedia
Active State Power Management or ASPM is a power management
protocol used to manage PCI Express
-based serial link devices as links become less active over time. It is normally used on laptop
s and other mobile Internet devices to extend battery life.
PCIe bus devices, such as IEEE1394
(FireWire), become less active, it is possible for the computer's power management system to take the opportunity to reduce overall power consumption by placing the link PHY into a low-power mode and instructing other devices on the link to follow suit. This is usually managed by the operating system
's power management software or through the BIOS
, thus different settings can be configured for laptop battery mode versus running from the battery charger
. Low power mode is often achieved by reducing or even stopping the serial bus clock as well as possibly powering down the PHY device itself.
While ASPM brings a reduction in power consumption, it can also result in increased latency
as the serial bus needs to be 'woken up' from low-power mode, possibly reconfigured and the host-to-device link re-established. This is known as ASPM exit latency and takes up valuable time which can be annoying to the end user if it is too obvious when it occurs. This may be acceptable for mobile computing, however, when battery life is critical.
Currently, two low power modes are specified by the PCIe 2.0 specification; L0s and L1 mode. The first mode concerns setting low power mode for one direction of the serial link only, usually downstream of the PHY controller. The second mode, L1, is bidirectional and results in greater power reductions though with the penalty of greater exit latency.
Power management
Power management is a feature of some electrical appliances, especially copiers, computers and computer peripherals such as monitors and printers, that turns off the power or switches the system to a low-power state when inactive. In computing this is known as PC power management and is built...
protocol used to manage PCI Express
PCI Express
PCI Express , officially abbreviated as PCIe, is a computer expansion card standard designed to replace the older PCI, PCI-X, and AGP bus standards...
-based serial link devices as links become less active over time. It is normally used on laptop
Laptop
A laptop, also called a notebook, is a personal computer for mobile use. A laptop integrates most of the typical components of a desktop computer, including a display, a keyboard, a pointing device and speakers into a single unit...
s and other mobile Internet devices to extend battery life.
Action
As serial-basedSerial communication
In telecommunication and computer science, serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. This is in contrast to parallel communication, where several bits are sent as a whole, on a link with several parallel channels...
PCIe bus devices, such as IEEE1394
IEEE 1394 interface
The IEEE 1394 interface is a serial bus interface standard for high-speed communications and isochronous real-time data transfer, frequently used by personal computers, as well as in digital audio, digital video, automotive, and aeronautics applications. The interface is also known by the brand...
(FireWire), become less active, it is possible for the computer's power management system to take the opportunity to reduce overall power consumption by placing the link PHY into a low-power mode and instructing other devices on the link to follow suit. This is usually managed by the operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
's power management software or through the BIOS
BIOS
In IBM PC compatible computers, the basic input/output system , also known as the System BIOS or ROM BIOS , is a de facto standard defining a firmware interface....
, thus different settings can be configured for laptop battery mode versus running from the battery charger
Battery charger
A battery charger is a device used to put energy into a secondary cell or rechargeable battery by forcing an electric current through it.The charge current depends upon the technology and capacity of the battery being charged...
. Low power mode is often achieved by reducing or even stopping the serial bus clock as well as possibly powering down the PHY device itself.
While ASPM brings a reduction in power consumption, it can also result in increased latency
Latency (engineering)
Latency is a measure of time delay experienced in a system, the precise definition of which depends on the system and the time being measured. Latencies may have different meaning in different contexts.-Packet-switched networks:...
as the serial bus needs to be 'woken up' from low-power mode, possibly reconfigured and the host-to-device link re-established. This is known as ASPM exit latency and takes up valuable time which can be annoying to the end user if it is too obvious when it occurs. This may be acceptable for mobile computing, however, when battery life is critical.
Currently, two low power modes are specified by the PCIe 2.0 specification; L0s and L1 mode. The first mode concerns setting low power mode for one direction of the serial link only, usually downstream of the PHY controller. The second mode, L1, is bidirectional and results in greater power reductions though with the penalty of greater exit latency.
External links
- PCI Express Specifications - PCI-SIGPCI-SIGThe PCI-SIG or Peripheral Component Interconnect Special Interest Group is an electronics industry consortium responsible for specifying the Peripheral Component Interconnect , PCI-X, and PCI Express computer buses....
- ASPM Optionality: update to ASPM specification
- Active State Power Management in Windows Vista - MicrosoftMicrosoftMicrosoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...