ACPI and Power Management Requirements

This section defines the system and BIOS requirements for ACPI and power management.

System design meets ACPI 1.0 and related requirements

Required for all server types, with additional requirements for SOHO servers

The system board set must support the Advanced Configuration and Power Interface Specification, Version 1.0 or later. This requirement ensures that the system correctly supports the Plug and Play and power-management functionality described in this guide.

ACPI support for all server systems must include the following required capabilities:

• A power-management timer. System control interrupt and necessary Status and Enable (STS/EN) bits must be provided.
  
  
• Support for a description table that defines the complete hierarchy for system-board devices, including host PCI bridges. The description table must include all non-Plug and Play devices to be enumerated and all other devices for which power management or removal capabilities have been added by the system-board design.
  
  
• Each bus and device enumerated using ACPI includes the ACPI control methods necessary to configure these devices. This includes requirements defined in these guidelines for automatic device configuration, resource allocation, and dynamic disable capabilities.

For information about Plug and Play support under Windows NT 5.0, see the Windows NT 5.0 DDK. Standard system devices are excluded from related requirements, as described in requirement #12, “System and device configuration meet Plug and Play requirements.”

• Thermal model and fan control, if implemented, comply with Section 12 of the ACPI 1.0 specification. Notice also that a server that supports thermal controls must have active thermal control such as a fan and cannot use passive thermal control under normal operating circumstances.

This requirement, however, does allow proprietary value-added features that cannot be implemented using ACPI. For example, systems are permitted to use out-of-band methods to provide cooling when the operating system is not booted.

• Support for at least one processor power state. This can be either C1, C2, or C3.
  
  
• No capabilities for the end user to disable system ACPI support using CMOS or other means. Disabling ACPI will cause boot failures when Windows NT relies on ACPI to identify and initialize system devices.

This requirement, however, does allow proprietary value-added features that cannot be implemented using ACPI.

The following ACPI support is required for SOHO servers and recommended for other server types:

• Power button in compliance with the ACPI 1.0 specification. This is described in requirement #9, “Hardware design supports OnNow initiative.”
  
  
• Real-time clock alarm that supports wake-up based on a scheduled time and day of the month. If this feature is implemented, the day-of-month feature is required under these guidelines, although it is an optional feature in the ACPI 1.0 specification. Also, if this feature is implemented, system control interrupt and necessary STS/EN bits must be provided.
  
  
• The S5 soft-off state, as required in the ACPI 1.0 specification. If a soft-off feature is supported, it must meet the requirements for the S5 state defined in the ACPI 1.0 specification. In addition, support for either the S1, S2, or S3 sleep state is recommended. Support for the S4 or S4BIOS states is optional.

Support for the S3 state (Suspend to RAM), which provides the optimal user experience and power savings, is likely to become a requirement in a future version of this design guide.

• USB host controller can wake the system. If a USB host controller is present in the system, it must support wake-up capabilities in one of the following system states: S1 or S2. Supporting wake-up from the S3 state is recommended.

Notice that if wake-up from the S2 or S3 state is supported, wake-up must be supported for all higher power sleep states. For example, if the controller supports wake-up from the S2 state, it must also support wakeup from the S1 state.

Note: System-board power management or configuration features implemented on a server system that are defined in the ACPI 1.0 specification must comply with ACPI 1.0, even if those features are not specific requirements or recommendations in these guidelines. This requirement, however, does allow proprietary value-added features that cannot be implemented using ACPI.

Hardware design supports OnNow initiative

Required for all server types, with additional requirements for SOHO servers

Elements of the OnNow design initiative ensure that the operating system and device drivers control the state of individual devices and the system board set.

All devices and drivers must support the D0 and D3 power states consistent with the definitions in the Default Class Power Management Specification and the relevant device class power management reference specification. This requirement must be implemented so that each device can successfully survive a system sleep/wake transition (device D3 to D0 transition) without requiring user intervention to restore functionality.

This requirement applies whether or not system power is removed while the computer is in an S1–S4 state. The operating system supports the S4 state without system-board support, so all devices and drivers must meet this requirement.

Notice that there is no power consumption requirement for devices in the D3 state. It is recommended, however, that devices implement the D3 state so that device power consumption is reduced to near zero, with the recognition that there is no requirement to retain any device context because it will be preserved or restored by the driver when returning to the D0 state.

It is recommended that devices and drivers support the D1, D2, or both low-power states, and that they support the defined wake-up events as designated in the relevant device class power management reference specification.

SOHO servers must, and all servers should, provide PCI, USB, and IEEE 1394 buses that support power management requirements, as defined in the related bus standards.

OnNow features that are required for SOHO servers (and that are optional for Basic and Enterprise servers) include the following:

• System provides one or more indicators to show whether the system is in the working or sleep state.

Recommended: A non-flashing, light-emitting diode (LED) sleep indicator that is a different color than the wake indicator. A slowly blinking LED indicator (less than 1 Hz) is also an acceptable implementation. This applies for S1, S2, and S3 system states.

The nonvolatile sleep state, S4 or S4BIOS, should appear to the user as the off state (S5); therefore, all of these states should have the same indicator.

• System provides software-controlled, ACPI-based power switch. The system should provide an easily accessible power switch that can be controlled by software and that supports the functionality required in Section 4.7.2.2.1 of the ACPI 1.0 specification.

The following provides implementation guidelines for the power switch:

• The power switch can be implemented as either a power button or a sleep button. The recommended implementation is to have both. If both buttons are implemented, the sleep button should be the user’s primary switch interface and must be easily distinguishable from the power button. The preferred implementation is to hide the power button.
  
  
• The function of these buttons is determined by the operating system. The default action for the sleep button is to cause the machine to enter a sleep state. The default action for the power button is to shut down the operating system and power off the machine.

  In a single-button configuration, the button can be used for either sleep/wake transitions (G0< – >G1/S1-S4) or off/on transitions

  (G0< – >G2/S5), depending on user preference and the policy set in the operating system.

  In a two-button configuration that includes separate power and sleep buttons, the user interface provided by the operating system will allow only the default actions.

• In case of a hardware or software failure that prevents normal operation of the software-controlled buttons, the switch capabilities must include an override mechanism for turning off the server.

  A 4-second override mechanism is recommended in Section 4.7.2.2.1 of the ACPI 1.0 specification. The override can be on either the power button or the sleep button in a two-button configuration, but it is recommended that the override be associated with the sleep button in order to establish an industry-standard implementation.

  An acceptable but not recommended alternative to the 4-second override is a separate hidden or recessed switch that cannot be mistaken for either the power button or the sleep button.

  Notice that the override mechanism is not an alternative way for the user to turn off the server in normal operation; it is only a fail-safe function for fault conditions.

• If the power switch is provided on the keyboard, the key must be clearly labeled and must consist of a single keystroke for turning on the server, to ensure accessibility for persons with disabilities. (Two keystrokes can be used to turn off the server.)

  For information about scan codes for keyboard power switches, see http://www.microsoft.com/hwdev/desinit/scancode.htm.

• The system power supply provides “standby” power for system wake-up events. A minimum of 720 mA of “standby” power is required to support wake-up devices on PCI or USB when the system is in the ACPI S3, S4, or S5 state. Additional information about this requirement can be found in Instantly Available PC System Power Delivery Requirements and Recommendations, at http://developer.intel.com/design/power/supply98.htm.

System startup meets requirements for OnNow support

This feature does not apply for DEC Alpha servers, except for the initial recommendation for fast power-on self test (POST).

The intention of this recommendation is to ensure that the end user is not presented with unnecessary visual displays and to ensure that access to error information remains available using a hot key.

The following support is suggested:

• BIOS supports fast POST. The system should be available to the user as quickly as possible. Although a specific time limit is not established, the basic recommendation is that power on to the bootstrap loader should occur within 5 seconds, plus hard-disk ready time, option ROMs, and time required for memory subsystem initialization and error correction code (ECC).

The following are recommended ways to reduce processing overhead to make system boot time as fast as possible:

• No video memory test and limited test for DRAM size.
  
  
• No tests for serial or parallel ports.
  
  
• No floppy disk test or media check (boot from hard disk only).
  
  
• No tests for hard disk controller or drive type (if the system does not include swappable drives).

Fast POST mode for BIOS can be disabled by the user for troubleshooting.

• Resume from sleep state (S1–S3) to operating system handoff should occur within 500 ms. This recommendation does not apply to the S4 state. For all other sleep states, the time to operating system handoff means when the processor starts running (first instruction) until the BIOS jumps to the Waking Vector in the ACPI firmware control structure table, as described in Section 5.2.6 in the ACPI 1.0 specification.
  
  
• Minimal startup display. System startup should draw the end user’s attention only when errors occur or when user action is needed.

The default configuration should allow a beep during the boot process only in case of an error, and the only screen display should be the OEM splash screen, which can include information such as copyright notices. By default, the system should be configured so the screen display does not show memory counts, device status, and so on. The display should present a “clean” BIOS startup so that the end user is not presented with cryptic and unnecessary information.

However, the system start-up process can include the following:

• A blank start-up screen.
  
  
• A hot-key override to display screen messages for troubleshooting or to display user-definable CMOS settings.
  
  
• Text-based, end-user action messages. Examples are: messages to display the setup hot key, the system help hot key, password entry, network log-on for remote booting, and so on.
  
  
• Manufacturer branding messages.
  
  
• A CMOS option to turn the clean start-up screen off and on.

Recommended for SOHO servers: Compliance with Simple Boot Flag Specification, Version 1.0 or later. This enables the BIOS to boot quickly when the last boot was successful and to perform diagnostics only if a problem occurred on the previous boot.