Chapter 21
Dynamic Bus Frequency Driver
21.1 Introduction
In order to improve power consumption, the Bus Frequency driver dynamically manages
the various system frequencies.
The frequency changes are transparent to the higher layers and require no intervention
from the drivers or middleware. Depending on activity of the peripheral devices and CPU
loading, the bus frequency driver varies the DDR frequency between 24MHz and its
maximum frequency. Similarly the AHB frequency is varied between 24MHz and
132MHz.
21.1.1 Operation
The Bus Frequency driver is part of the power management module in the Linux BSP.
The main purpose of this driver is to scale the various operating frequency of the system
clocks (like AHB, DDR, AXI etc) based on peripheral activity and CPU loading.
21.1.2 Software Operation
The bus frequency depends on the usecount of the various clocks in the system for its
operation. Drivers enable/disable their clocks based on peripheral activity. Every
peripheral is associated with a frequency setpoint. The bus frequency will set the system
frequency to highest frequency setpoint based on the peripherals that are currently active.
The following setpoints are defined for all i.MX 6 platforms:
1. High Frequency Setpoint: AHB is at 132MHz, AXI is at 264Mhz and DDR is at the
maximum frequency. This mode is used when most periphrals that need higher frequency
for good performance are active. For ex, video playback, graphics processing etc.
i.MX 6Solo/6DualLite Linux Reference Manual, Rev. L3.0.35_4.1.0, 09/2013
Freescale Semiconductor, Inc.
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