SMBus Interface
7 SMBus Interface
The Intel 6400/6402 Advanced Memory Buffer (AMB) has configuration registers that
provide flexibility and allow for testing and optimization of the chip. Upon system reset
(RESET#), configuration registers are reset to predetermined default states,
representing the minimum feature set required to successfully bring up a nominal
channel. It is expected that the BIOS will properly determine and program the optimal
configuration settings.
For all of these registers, the AMB supports register access mechanisms through SMBus
as well as through in-band channel commands.
7.1
System Management Access
System Management software in the platform can initiate system management access
to the configuration registers. This can be done through SMBus accesses.
The mechanism for the Server Management (SM) software to access configuration
registers is through a SMBus Specification, Rev. 2.0-compliant slave port. The AMB
contain this slave port and allow access to the configuration registers.
SMBus operations are made up of two major steps: (1) writing information to registers
within each component and (2) reading configuration registers from each component.
The following sections will describe the protocol for an SMBus master to access a AMB’s
internal configuration registers. Refer to the SMBus Specification, Rev. 2.0 for the bus
protocol, timings, and waveforms.
7.1.1
SMBus 2.0 Specification Compatibility
The principal requirement from the SMBus 2.0 specification is support of the “high
power” bus electrical specifications described in the layer 1 (Physical layer) chapter.
For the simple register access requirements of FBD, no layer 2 (Link layer) or layer 3
(Network layer) extensions provided by the 2.0 specification are used. In particular,
there is no support for Address Resolution Protocol (ARP) since FBD is using fixed
addresses. Additionally, only a subset of the network packet protocols described in the
specification are needed and these are described below.
AMB’s are required to support read and write transactions without requiring clock
stretching in order to simplify host controller requirements. For similar reasons, AMB’s
should not master SMBus transactions in normal operation.
7.1.2
Supported SMBus Commands
The AMB SMBus Rev. 2.0 slave ports support register reads and writes built out of the
following SMBus primitive commands:
The slave address for each primitive SMBus transaction are determined from the SA
pins.
• For normal FBD DIMMs:
— Slave Address[6:3] = 4’b1011
— Slave Address[2:0] = SA[2:0]
Intel® 6400/6402 Advanced Memory Buffer Datasheet
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