Hardware Reference
In-Depth Information
Table 6.5
Status transition by fps control
Workload (fps)
25
20
15
10
5
10
15
20
25
CPU #0 (MHz)
600
300
300
150
150
150
300
300
600
CPU #1 (MHz)
600
300
300
300
75
300
300
300
600
CPU #2 (MHz)
600
600
150
150
75
150
150
600
600
CPU #3 (MHz)
600
300
300
150
75
150
300
300
600
Total (MHz)
2,400
1,500
1,050
750
375
750
1,050
1,500
2,400
Voltage (V)
1.4
1.4
1.2
1.2
1.0
1.2
1.2
1.4
1.4
Power (W)
4.4
3.5
1.8
1.7
0.8
1.7
1.8
3.5
4.4
Battery Life and Temperature Controls Using Idle Reduction Framework
The CPUfreq framework has been used in general for laptop personal computers
with an AC adapter or a battery. The CPUfreq receives data on the activation status
of the AC adapter and the remaining battery life. If the AC adapter is activated, the
CPUfreq disregards the battery life. If the AC adapter is not activated, the CPUfreq
takes the battery life into consideration when choosing a governor.
The CPUfreq also takes the temperature around the board into consideration in
the choice of a governor. Heat is generated by the power consumption of the semi-
conductors. The temperature of the semiconductors can exceed the upper bound at
which normal operation of the semiconductors is not guaranteed. A processor is
usually the main source of on the board. However, a processor with the DVFS capa-
bility and multiple power domains can control the amount of heat radiation and
power consumption.
The power control manager daemon controls both the CPUfreq and the CPU
Hot-plug frameworks depending on the activation status of the AC adapter,
remaining battery life, and the temperature around the board. The activation status
of the AC adapter is represented by the value of a DIP switch on the RP-2 board.
The value, 0 or 1, of the DIP switch is read from one bit of a general-purpose
input/output (GPIO) port. If the AC adapter is activated, the battery life is ignored.
The battery life is translated from the voltage of the battery. A battery manufac-
turer supplies a datasheet on which a graph shows the correspondence between
the remaining battery life and the output voltage. We have developed a battery life
and output voltage model from a battery currently on the market. We used a DC
power unit with variable voltage output instead of a battery because the charge or
discharge time of a battery takes too long to test or demonstrate the control that
depends on the battery life.
The temperature is measured by a heat sensor, which can be either inside or out-
side the chip. We used a heat sensor outside the RP-2 chip. The power unit of the
RP-2 board is compatible with that of the Advanced Technology extended (ATX)
PC motherboard. The ATX PC power unit made for the automobile PC takes DC
current from a battery and generates power that is compatible with the ATX PC
power unit. The advantage of this power unit is that it has both a voltage sensor and
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