Samsung S5PC100 User Manual page 202

S5PC100 USER'S MANUAL (REV1.0)
2 FUNCTION DESCRIPTION
There are two types of power consumption namely static and dynamic.. Static power is consumed if power to a
circuit is supplied and there is no active operation in the circuit. Dynamic power is consumed if the signal to a
circuit is toggling, and there is some active operation in the circuit. The static power consumption is due to leakage
current in the process while the dynamic power consumption is due to charging and discharging of capacitors. The
dynamic power consumption depends on operating voltage, operating frequency, and toggling ratios of the logic
gate.
Various power-saving techniques have been developed and they are listed in Table 2.4-1.
Power saving
techniques
Frequency scaling
Clock off
Power off
External power off
Frequency scaling means that the frequency of clock to a specific Intellectual Property (IP) module is lowered if
the module is not required to run fast. Frequency scaling reduces dynamic power.
Clock off means that clock gating cells in Clock Controller is used to disable clock to a specific IP module. These
clock gating cells are controlled by setting registers (CLK_GATE_D0_0-2, CLK_GATE_D1_0-5, and
CLK_GATE_SCLK_0-1) in Clock Controller. If clock off is applied, power to logic gate is still supplied, and
therefore the states of Normal F/F (Flip-Flop) and Retention F/F are maintained. Retention F/F is developed to
meet special purpose to keep its state although power is not supplied due to power off.
Power off means that current path to a specific power domain (a group of IP modules) is internally disconnected
using switch cells in that power domain. Therefore power to that domain is not supplied.
The switch cells are controlled by setting registers (NORMAL_CFG, and STOP_CFG) in PMU. Note that external
power to S5PC100 is not off. Therefore, there can be two power off techniques as listed below.
• Power off without state retention
♦ Normal F/F is used. ♦ Wakeup reset is necessary.
• Power off with state retention
♦ Retention F/F is used. ♦ Wakeup reset is not necessary.
The power off does not preserve the state of normal F/F in the power-down domain. A power domain except TOP
domain has only normal F/F, and does not have retention F/F. Therefore, sub-domain, power domain except TOP
domain, does not preserve the state of F/F when the sub-domain is power-off. If a sub-domain is powered up
again, a wakeup reset is invoked for the modules in the sub-domain.
But, top domain has both normal F/F and retention F/F, and each module in top domain has only normal F/F or
retention F/F. It is not the case that a module has both normal F/F and retention F/F. Therefore, the module that
Table 2.4-1 Comparison of Power Saving Techniques
Result
Reduce dynamic power
Minimize dynamic power
Minimize leakage power
Nearly zero power
Clock Power
Enable Supplied
Disable Supplied
Not supplied
Disable
(internally off)
Not supplied
Disable
(externally off)
Power Management
State Retention
Normal F/F Retention F/F
Keep state
Keep state
Lose state Keep state
Lose state
2.4-3