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SYM53C876/876E Data Manual
Functional Description
Power Management
Power Management
The SYM53C876E complies with the PCI Bus
Power Management Interface Specification, Revi-
sion 1.0. The PCI Function Power States are
defined in that specification: D0, D1, D2, and
D3. D0 is the maximum powered state, and D3 is
the minimum powered state. Power state D3 is
further categorized as D3hot or D3cold.
The SYM53C876E power states are indepen-
dently controlled through two power state bits
that are located in the PCI Configuration Space
Register 44h.
Although the PCI Bus Power Management Inter-
face Specification does not allow power state tran-
sitions D2 ---> D1, D3 ---> D2, or D3 ---> D1,
the SYM53C876E hardware places no restriction
on transitions between power states.
As the device transitions from one power level to a
lower one, the attributes that occur from the
higher power state level are carried over into the
lower power state level. For example, D1 disables
the SCSI CLK. Therefore, D2 will include this
attribute as well as the attributes defined in the
Power State D2 section. The PCI Function Power
States--D0, D1, D2, and D3--are described below
in conjunction with each SCSI function. Power
state actions are separate for each function.
Power State D0
Power state D0 is the maximum power state and is
the power-up default state for each function.
Power State D1
Power state D1 is a lower power state than D0. A
function in this state is considered to be in snooze
mode and disables the SCSI CLK. In snooze
mode, a SCSI reset does not generate an /IRQ
signal. However, by setting the Wakeup Interrupt
Enable bit (bit 3 in the SIEN1 register), then a
SCSI reset generates an /IRQ signal, but SCSI
CLK is still disabled.
Power State D2
Power state D2 is a lower power state than D1. A
function in this state is considered to be in coma
mode. The following PCI Configuration Space
command register enable bits are suppressed:
n
I/O Space Enable
n
Memory Space Enable
n
Bus Mastering Enable
n
SERR
n
PERR
Thus, the function’s memory and I/O spaces can-
not be accessed, and the function cannot be a PCI
bus master. Furthermore, SCSI & DMA inter-
rupts are disabled when the function is in power
state D2. If the function is transitioned from
power state D2 to power state D1 or D0, the pre-
vious values of the PCI command register are
restored. Also, any pending interrupts before the
function entered power state D2 are asserted.
Power State D3
Power state D3 is the minimum power state,
which includes subsettings called D3hot and
D3cold. D3hot allows the device to transition to
Table 2-8: Power States
Config. Reg 44h
Bits
Power State
Function
00
D0
Maximum Power
01
D1
Disables SCSI
clock
10
D2
Coma Mode
11
D3
Minimum Power