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Chapter 4 Power Management 13
25175H—March 2003 AMD Athlon™ XP Processor Model 8 Data Sheet
Preliminary Information
The Northbridge contains BIOS programmable registers to
enable the system bus disconnect in response to Halt and Stop
Grant special cycles. When the Northbridge receives the Halt or
Stop Grant special cycle from the processor and, if there are no
outstanding probes or data movements, the Northbridge
deasserts CONNECT a minimum of eight SYSCLK periods after
the last command sent to the processor. The processor detects
the deassertion of CONNECT on a rising edge of SYSCLK and
deasserts PROCRDY to the Northbridge. In return, the
Northbridge asserts CLKFWDRST in anticipation of
reestablishing a connection at some later point.
Note: The Northbridge must disconnect the processor from the
AMD Athlon system bus before issuing the Stop Grant
special cycle to the PCI bus or passing the Stop Grant special
cycle to the Southbridge for systems that connect to the
Southbridge with HyperTransport™ technology.
This note applies to current chipset implementation—
alternate chipset implementations that do not require this
are possible.
Note: In response to Halt special cycles, the Northbridge passes the
Halt special cycle to the PCI bus or Southbridge
immediately.
The processor can receive an interrupt after it sends a Halt
special cycle, or STPCLK# deassertion after it sends a Stop
Grant special cycle to the Northbridge but before the
disconnect actually occurs. In this case, the processor sends the
Connect special cycle to the Northbridge, rather than
continuing with the disconnect sequence. In response to the
Connect special cycle, the Northbridge cancels the disconnect
request.
The system is required to assert the CONNECT signal before
returning the C-bit for the connect special cycle (assuming
CONNECT has been deasserted).
For more information, see the AMD Athlon™ System Bus
Specification, order# 21902 for the definition of the C-bit and
the Connect special cycle.