Active-state power management (ASPM) is a

power management Power management is a feature of some electrical appliances, especially copiers, computers, computer CPUs, computer GPUs and computer peripherals such as monitors and printers, that turns off the power or switches the system to a low-power st ...

mechanism for

PCI Express PCI Express (Peripheral Component Interconnect Express), officially abbreviated as PCIe or PCI-e, is a high-speed serial computer expansion bus standard, designed to replace the older PCI, PCI-X and AGP bus standards. It is the common ...

devices to garner power savings while otherwise in a fully active state. Predominantly, this is achieved through active-state link power management; i.e., the PCI Express serial link is powered down when there is no traffic across it. It is normally used on

laptop A laptop, laptop computer, or notebook computer is a small, portable personal computer (PC) with a screen and alphanumeric keyboard. Laptops typically have a clam shell form factor with the screen mounted on the inside of the upper li ...

s and other

mobile Internet device A mobile Internet device (MID) is a multimedia capable mobile device providing wireless Internet access. They are designed to provide entertainment, information and location-based services for personal or business use. They allow 2-way communica ...

s to extend battery life. As serial-based PCI Express devices 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 An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...

's power management software or through the

BIOS In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the b ...

, thus different settings can be configured for laptop battery mode versus running from the

battery charger A battery charger, recharger, or simply charger is a device that stores energy in a battery by running an electric current through it. The charging protocol (how much voltage or current for how long, and what to do when charging is complete) depe ...

. 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 PCI Express 2.0 specification; L0s and L1 mode. L0s concerns setting low power mode for one direction of the serial link only, usually downstream of the PHY controller. L1 shuts off PCI Express link completely, including the reference clock signal, until a dedicated signal (CLKREQ#) is asserted, and results in greater power reductions though with the penalty of greater exit latency.

External links

* * Active State Power Management Active State Power Management {{compu-hardware-stub BIOS Unified Extensible Firmware Interface Peripheral Component Interconnect

See also

External links