
Chapter 10. Power and Thermal Management
10-3
Programmable Power Modes
The following sections describe the characteristics of the power management modes, the
requirements for entering and exiting the various modes, and the capabilities available for
each mode.
10.2.1 Full-Power Mode with Dynamic Power Management
Disabled
Full-power mode with dynamic power management disabled is selected when the
HID0[DPM] = 0 and has the following characteristics:
¥
¥
Default state after power-up and HRESET
All functional units operate at full processor speed at all times
10.2.2 Full-Power Mode with Dynamic Power Management
Enabled
Full-power mode with dynamic power management enabled (HID0[DPM] = 1) provides
on-chip power management without affecting functionality or performance, and has the
following characteristics:
¥
¥
¥
¥
Functional units are clocked only when needed.
Required functional units operate at full processor speed.
No software or hardware intervention is required after the mode is set.
Power management is transparent to software and hardware.
10.2.3 Doze Mode
Doze mode disables most functional units but maintains cache coherency by enabling the
bus interface unit and snooping (L1 and L2 caches and snooping logic). A snoop hit causes
the MPC7400 to enable the caches, copy the data back to memory, disable the caches, and
fully return to the doze state.
Note the following with respect to doze mode:
¥
Most functional units are disabled (excluding thermal assist unit, performance
monitor, bus snooping, time base, and decrementer).
Phase-locked loop (PLL) and delay-locked loop (DLL) are running and locked to
SYSCLK.
¥
10.2.3.1 Entering Doze Mode
Doze mode is entered by setting the doze bit (HID0[8] = 1), clearing the nap and sleep bits
(HID0[9] and HID0[10] = 0), and setting MSR[POW]. The MPC7400 enters doze mode
after several processor clocks.