Specifications

78 AMD Geode™ GeodeROM Functional Specification
PCI Support
32087C
7.1.4 Subfunction 06h - Generate Special Cycle
Description:
The PCI host controller has the ability to broadcast messages across the entire bus by issuing special cycles. When a
special cycle occurs, devices on the bus can monitor the message, but must not acknowledge the message by assert-
ing their DEVSEL# (Device Select) signal. PCI devices do not have to respond to special cycles. If a device is capable
of responding to special cycles, the system configurator or PCI BIOS enables this capability in a device by setting bit
three of its Configuration Space Command register to ‘1’.
Passed:
Returns:
Special cycle messages consist of a 16-bit message field, that the host controller asserts on address/data lines AD[15:0],
and a message field that is asserted in signals AD[31:16]. The meaning of each message field is determined by the PCI
SIG and a list of all valid special cycles appears in the PCI Local Bus Specification. Revisions 2.0 and 2.1 of the PCI Local
Bus Specification define the following special cycle messages:
• 0000h: System Shutdown
• 0001h: PCI Bus Halt
• 0002h: Intel x86 Architecture-Specific message
• 0003h-FFFFh: Reserved
One useful application of special cycle messages is to broadcast a pending system shutdown to PCI bus devices. For
example, a PCI network controller should immediately abort its current network activity in the event of a system shutdown.
It is the responsibility of the operating system to issue a PCI BIOS call to generate the system shutdown message (0000h).
Parameter Description
AH B1h (PCI Function ID)
AL 06h (Generate Special Cycle)
BH Bus number on which to assert the cycle (0-FFh)
EDX Special Cycle Data:
Bits [15:0] = Special cycle message
Bits [31:16] = Message specific data
Parameter Description
CF Function completion status:
0 if function completed successfully
1 if an error occurred, AH contains error code
AH Function return status codes: See AH in Section 7.1.2 "Subfunction 02h - Find PCI Device" on page
76.