Datasheet

VIPER / VIPER-Lite Embedded Linux Development Kit Quickstart Arcom Embedded Linux (AEL)
The default on the VIPER is to use the performance governor with a maximum
frequency of 400MHz. The maximum frequency on the VIPER-Lite is limited to 200MHz
by passing a command line parameter to the Linux kernel. Please refer to the Software
configuration section on page 28 for further information. The powersave and userspace
governors are supplied as loadable kernel modules, called cpufreq_powersave and
cpufreq_userspace respectively. They may be loaded using the modprobe command.
The available performance clock rates are listed in the following table. They correspond
to the modes available when the turbo mode multiplier, CCCR[N] is 1.0.
Clock speed
(KHz)
Core Clock Configuration
Register(L, M and N multipliers)
Memory
clock (MHz)
Run clock
(MHz)
Turbo clock
(MHz)
PX bus
(MHz)
99532 27, 1, 1.0 99 99 99 50
199065 27, 2, 1.0 99 199 199 99
398131* 27, 4, 1.0 99 398 398 196
The available powersave clock rates are listed in the following table:
Clock speed
(KHz)
Core Clock Configuration Register
(L, M and N multipliers)
Memory
clock (MHz)
Run clock
(MHz)
Turbo clock
(MHz)
PX bus
(MHz)
99532 27, 1, 1.0 99 99 99 50
199065 27, 1, 2.0 99 99 199 50
298598 27, 1, 3.0 99 99 299 50
398131 27, 2, 2.0 99 199 398 99
The cpufreq-set utility can be used to select a governor and to set the minimum and
maximum allowable frequency. This is illustrated by the following examples:
To select the performance governor and limit the maximum allowed speed to 200MHz: •
•
•
# cpufreq-set --governor performance --max 199065
To select the powersave governor and set the minimum allowed frequency to 300MHz:
# modprobe cpufreq_powersave
# cpufreq-set –governor powersave --min 298598
To use the userspace governor and set a frequency of 400MHz:
# modprobe cpufreq_userspace
# cpufreq-set --governor userspace --freq 398131
Changing the clock frequency automatically regulates the core voltage in order to
maximize power savings.
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© 2006 Arcom Issue B 23