Example Low Power Use Cases - Texas Instruments AM335 Series Design Manual

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3.3.4 Linux Debug Features
Linux provides some interfaces to diagnose system issues, although none of them are specifically oriented
towards power, they can provide some useful insight on what Linux is trying to do with the underlying
hardware.
3.3.4.1 Checking Kernel Boot Arguments
If kernel boot arguments are modified to enable certain features, it might be necessary to confirm the
exact boot command line argument used. This information is available in
$ cat /proc/cmdline
console=tty0 console=ttyO0,115200n8 root=/dev/mmcblk0p1 rootfstype=ext4 rootwait coherent_pool=1M
quiet cape_universal=enable
3.3.4.2 Serial Console Output During Suspend/Resume
Sometimes it is helpful when debugging a suspend or resume issue to have console output throughout the
whole process. To enable this, add no_console_suspend to the kernel boot arguments. This is most easily
done by modifying the bootargs variable in U-Boot.
Note that if this is used then the serial port cannot be used as a wakeup source for the processor.
3.3.4.3 Sysfs Debug Interface
The kernel exposes debug information using the sysfs system. This information is available in
/sys/kernel/debug
$ cat /sys/kernel/debug/clk/clk_summary
This displays every clock in the system, and whether or not it has any consumers.
3.3.4.4 Low Power Debugging
During development, debugging suspend/ resume issues can be challenging due to the nature of low
power modes, and limited debugging ability. The wiki link below is geared toward Linux developers using
the AM335x family of embedded processors. Many of the topics contained in the page, however, will still
apply to users of other operating systems. The goal of this page is to provide some insight into common
issues they might bump into, as well as tools to help identify issues. For more information, see
Debugging_AM335x_Suspend-Resume_Issues.
4

Example Low Power Use Cases

This section highlights low power use cases using the techniques presented in
Use cases that require low power while only needing a subset of SoC peripherals are prime candidates for
targeted system power optimization. Modifications to the processor's internal bus speeds (L3, DDR, and
so forth) and disabling unused peripherals are some of the basic knobs available to the end user.
The AM335x EVM and Processor SDK are presented as a baseline starting point. The EVM and
Processor SDK are designed to showcase full functionality and performance, thus, it is not optimized for
any specific application.
To demonstrate the low power capabilities of the AM335x, two optimized device trees for the AM335x GP
EVM are used to disable many of the unnecessary peripherals. Although these examples will not cover all
of the optimizations possible, the optimizations used are easily reproducible and can serve as a good
starting point for an engineer creating a low power system. The process of selecting these device trees is
documented and some runtime adjustments that may be needed, so that the designer can follow along
and try out these optimizations for themselves.
SPRAC74A – February 2017 – Revised March 2017
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. One useful interface here is the clock summary:
Copyright © 2017, Texas Instruments Incorporated
Example Low Power Use Cases
:
/proc/cmdline
Section 2 and Section
AM335x Low Power Design Guide
3.
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