JAJSQ97J may 2009 – january 2021 XIO2001
PRODUCTION DATA
The PCI Express Specification provides a method for devices to limit internal functionality and save power based on the value programmed into the captured slot power limit scale (CSPLS) and capture slot power limit value (CSPLV) fields of the PCI Express device capabilities register at offset 74h. See Section 8.4.50, Device Capabilities Register, for details. The bridge writes these fields when a set slot power limit message is received on the PCI Express interface.
After the deassertion of PERST, the XIO2001 compares the information within the CSPLS and CSPLV fields of the device capabilities register to the minimum power scale (MIN_POWER_SCALE) and minimum power value (MIN_POWER_VALUE) fields in the general control register at offset D4h. See Section 8.4.66, General Control Register, for details. If the CSPLS and CSPLV fields are less than the MIN_POWER_SCALE and MIN_POWER_VALUE fields, respectively, then the bridge takes the appropriate action that is defined below.
The power usage action is programmable within the bridge. The general control register includes a 3-bit POWER_OVRD field. This field is programmable to the following options: