82870P2P64H2 Datasheet, PDF (169/217 Pages) –

Functional Description
R
In other examples not shown here, the SMBus master may not necessarily program all registers as
shown in the above figure. For example, if a master is performing a series of DWord writes to the
same device (same bus number, device number, and function number), the SMBus master will
write the register index to “03h” (register number) and start with the register number, then its data.
There is no need for it to reprogram the command, bus number, or device/function number
because these are not changing.
In Figure 14 an initiator targets the P64H2 with a write to the Index Register (in this case the data
offset 04h, then does a start repeat with a read. The P64H2 will return data as long as the master
ACKs.
When writing a register in ICH mode, the first byte after the index register will be the byte count.
It should be discarded on writes, and a value of 04h returned on reads, and the index pointer
should not be incremented for this byte.
Figure 14. Reading A Register
S
Slave Address
WA
0000_0100 (Register Index) A
Sr
Slave Address
RA
Data from Index
A
Data from (Index + 1)
A
Data from (Index + 2)
A
Data from (Index + 3)
A
... Data from (Index + N)
N
smbus_reading_A
4.7.1.4
4.7.1.5
Configuration Space Registers
PCI Configuration space registers are accessed directly by programming the bus number, device
number, and register number fields with the appropriate data. The bridge and I/OxAPICs are on
the primary bus, and the hot plug controllers are on the secondary bus.
Memory Space Registers
Accessing memory space registers is a little more complicated. The SMBus protocol implemented
by the server management chips can only access configuration space. As a result, memory space
needs to be accessed indirectly. The hot plug and I/OxAPIC functions, therefore, have aliases in
configuration space to allow these indirect accesses to their memory space registers. See the hot
plug and I/OxAPIC chapters for how the memory space aliases work.
Intel^® 82870P2 P64H2 Datasheet
169