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Raspberry Pi 3 B - power optimizations and boot adjustments

Raspberry Pi overview

grafik.png

Image source: https://www.elektronik-kompendium.de/sites/raspberry-pi/1905251.htm

HDMI deactivation

HDMI is disabled by default if no monitor is connected. If a monitor is connected this can be either enabled or disabled manually by the following commands

/opt/vc/bin/tvservice -o
#or sh vcgencmd display_power 1

#re-enable with
sudo /opt/vc/bin/tvservice -p

Bluetooth and WiFi deactivation (this is not going to be applied to Trikarus!)

vim /boot/config.txt
#dtoverlay=disable-wifi #enabled again! (backup remote connection)
#dtoverlay=disable-bt #enabled again! (filament weigh sub project requires to have it enabled)

Status LED deactivation (saves ~30 mA)


Red PWR LED

  • on if power OK
  • flashes (or goes out) if the power drops below about 4.63V

Green ACT LED

  • steady on if no SD card during boot

  • irregular flashes for SD card access

Ethernet Socket Left LED (yellow)

  • on 100-Mbps connection

  • off 10-Mbps connection

Ethernet Socket Right LED (green)

Version 1 (is not used)

vim /boot/config.txt
dtparam=act_led_trigger=none
dtparam=act_led_activelow=on

Version 2 (is used)

vim /opt/disable_leds.sh
#!/bin/bash
echo none > /sys/class/leds/led0/trigger
echo none > /sys/class/leds/led1/trigger
echo 0 > /sys/class/leds/led0/brightness
echo 0 > /sys/class/leds/led1/brightness
chmod +x /opt/disable_leds.sh
vim /etc/cron.d/disable_leds
# this script disables Raspberry Pi LEDs after bootup
SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
*/1 * * * *     root  /opt/disable_leds.sh

CPU throttling (this is not going to be applied to Trikarus!)

vim /boot/config.txt
arm_freq_min=250
core_freq_min=100
sdram_freq_min=150
over_voltage_min=0

USB deactivation

See Smart Stepper - USB, Soft and hard reset for USB scripts

Audio deactivation

vim /boot/config.txt
dtparam=audio=off

USB power and Raspberry Pi undervoltage

It seems possible to reduce the total allowed load from 1200 mA to 600 mA → https://www.raspberrypi.org/documentation/configuration/config-txt/misc.md

It was tested but seems to make no difference. So it was not applied to Trikarus configuration

max_usb_current=1 #1200 mA
max_usb_current=0 #600 mA

Problem description

  • dmesg shows detected undervoltage at startup
  • Monitoring shows the same undervoltage peak

Webcam might not be available due to error while adressing USB devices

[ 55.651885] usb 1-1.5: device not accepting address 11, error -110
[ 55.751888] usb 1-1.5: new high-speed USB device number 13 using dwc_otg
[ 66.291906] usb 1-1.5: device not accepting address 13, error -110
[ 66.292050] usb 1-1-port5: unable to enumerate USB device

Solution

GPU memory and troubleshooting "failed to open VCHI service (-1)"

This is okay/harmless message. The GPU memory was set to 16 MB in /boot/config.txt so some services are not available with such low memory.

/boot/config.txt Overview

Some default values were changed to the following:

dtparam=i2c_arm=on
dtparam=audio=off
gpu_mem=16 #GUI not used so use the memory for better things
boot_delay=3 #did not really help to omit the once per bootup occuring undervoltage but may help to wait for connected USB Stick

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