The Power Budget Capabilities Register Set

These registers permit power budgeting software to allocate power more effectively based on information provided by the device through its power budget data select and data register. This feature is similar to the data select and data fields within the power management capability registers. However, the power budget registers provide more detailed information that is useful to software when determining the effects of expansion cards that are added during runtime on the system power budget and cooling requirements. Through this capability, a device can report the power it consumes:

• from each power rail

• in various power management states

• in different operating conditions

These registers are not required for devices implemented on the system board or on expansion devices that do not support hot plug. Figure 15-4 on page 565 illustrates the power budget capabilities register set and shows the data select and data field that provide the method for accessing the power budget information.

The power budget information is maintained within a table that consists of one or more 32-bit entries. Each table entry contains power budget information for the different operating modes supported by the device. Each table entry is selected via the data select field, and the selected entry is then read from the data field. The index values start at zero and are implemented in sequential order. When a selected index returns all zeros in the data field, the end of the power budget table has been located. Figure 15-5 on page 566 illustrates the format and types of information available from the data field.