Bus Master Cycles; Lpc Power Management; Configuration And Pch Implications; I/O Cycles - Intel 6 SERIES CHIPSET - DATASHEET 01-2011 Datasheet

Functional Description
5.4.1.9

I/O Cycles

For I/O cycles targeting registers specified in the PCH's decode ranges, the PCH
performs I/O cycles as defined in the Low Pin Count Interface Specification, Revision
1.1. These are 8-bit transfers. If the processor attempts a 16-bit or 32-bit transfer, the
PCH breaks the cycle up into multiple 8-bit transfers to consecutive I/O addresses.
Note: If the cycle is not claimed by any peripheral (and subsequently aborted), the PCH
returns a value of all 1s (FFh) to the processor. This is to maintain compatibility with
ISA I/O cycles where pull-up resistors would keep the bus high if no device responds.
5.4.1.10

Bus Master Cycles

The PCH supports Bus Master cycles and requests (using LDRQ#) as defined in the Low
Pin Count Interface Specification, Revision 1.1. The PCH has two LDRQ# inputs, and
thus supports two separate bus master devices. It uses the associated START fields for
Bus Master 0 (0010b) or Bus Master 1 (0011b).
Note: The PCH does not support LPC Bus Masters performing I/O cycles. LPC Bus Masters
should only perform memory read or memory write cycles.
5.4.1.11

LPC Power Management

LPCPD# Protocol
Same timings as for SUS_STAT#. Upon driving SUS_STAT# low, LPC peripherals drive
LDRQ# low or tri-state it. The PCH shuts off the LDRQ# input buffers. After driving
SUS_STAT# active, the PCH drives LFRAME# low, and tri-states (or drives low)
LAD[3:0].
Note: The Low Pin Count Interface Specification, Revision 1.1 defines the LPCPD# protocol
where there is at least 30 µs from LPCPD# assertion to LRST# assertion. This
specification explicitly states that this protocol only applies to entry/exit of low power
states which does not include asynchronous reset events. The PCH asserts both
SUS_STAT# (connects to LPCPD#) and PLTRST# (connects to LRST#) at the same time
during a global reset. This is not inconsistent with the LPC LPCPD# protocol.
5.4.1.12

Configuration and PCH Implications

LPC I/F Decoders
To allow the I/O cycles and memory mapped cycles to go to the LPC interface, the PCH
includes several decoders. During configuration, the PCH must be programmed with the
same decode ranges as the peripheral. The decoders are programmed using the Device
31:Function 0 configuration space.
Note: The PCH cannot accept PCI write cycles from PCI-to-PCI bridges or devices with similar
characteristics (specifically those with a "Retry Read" feature which is enabled) to an
LPC device if there is an outstanding LPC read cycle towards the same PCI device or
bridge. These cycles are not part of normal system operation, but may be encountered
as part of platform validation testing using custom test fixtures.
Bus Master Device Mapping and START Fields
Bus Masters must have a unique START field. In the case of the PCH that supports two
LPC bus masters, it drives 0010 for the START field for grants to Bus Master 0
(requested using LDRQ0#) and 0011 for grants to Bus Master 1 (requested using
LDRQ1#.). Thus, no registers are needed to configure the START fields for a particular
bus master.
Datasheet 133