Texas Instruments AM335 Series Design Manual page 24

Example Low Power Use Cases
Using the device tree optimizations, a hypothetical minimal use case is defined where a large portion of
peripherals are disabled and the power consumption is recorded. From here, specific sets of peripherals
are enabled to demonstrate increasing levels of functionality, while documenting the increasing power
demands of the system. By enabling devices on an "as-needed" basis, it is ensured that no extra
peripherals are there to consume power without adding any functionality to the system. In an actual
design, the developer must go through and make their own decisions on what a minimal system may look
like. For a true low power system, such an approach is recommended.
From the baseline system the following scenarios are covered:
• Baseline OS Idle
• Networked OS Idle
• Heavy CPU Load (Dhrystone)
• Heavy Ethernet Traffic (IPerf)
• Multimedia Playback
For un-optimized power figures from similar benchmarks, check the Linux Performance Wiki:
SDK Linux Kernel Performance
4.1 Device Setup Summary
To ensure consistency, the exact devices, software and OPP tables are documented here.
Demonstration Hardware
• AM335x GP EVM
• Modified Beaglebone Black (see below)
• FTDI USB to UART adapter
• Linux Host with TI Linux Procesor SDK v3.0.1 (Kernel 4.4.19) installed
• Keithley 2400 digital multimeter
Hardware Summary
The standard AM335x GP EVM was used for these tests. Additionally, the BeagleBone Black was used to
compare power consumption of different DDR topologies.
• Measurements were taken on the bench at room temperature
• BeagleBone Black DDR I/O and memory supply (VDCDC1) was severed from the PMIC at R6, and
was sourced and measured externally with a calibrated Keithley 2400-series source meter, using 4-
wire sensing.
Software Summary
The TI Linux Processor SDK version 3.0.1 was used with several minor tweaks to both Linux and U-Boot
to achieve lower power. The same SD card was used on both AM335x GP EVM and BeagleBone Black.
• U-Boot version 2016.05
– DDR frequency set to 303MHz for BeagleBone Black to match AM335x GP EVM
• Linux Kernel version 4.4.19
– Minimal device tree used (Ethernet, UART0, I2C0 enabled, other peripherals marked disabled)
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AM335x Low Power Design Guide
Guide.
Copyright © 2017, Texas Instruments Incorporated
SPRAC74A – February 2017 – Revised March 2017
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