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Undervoltage warning

If the power supply to the Raspberry Pi drops below 4.63V (+/-5%), the following icon is displayed. 

$ sudo nano /boot/config.txt

# Disable under-voltage warning

avoid_warnings=1 

Power: Ensure you have a good power supply which can steadily supply at least 2A at 5V. Many power supplies sag voltage and current under maximum load. If you see a lightning bolt icon or rainbow square in the top right corner during regular operation, this is the under-voltage warning and you are not supplying enough power. If you have USB devices plugged into the USB ports, considering getting a good powered USB hub to reduce power draw on the Pi. 

aha so power brownout

Probably, although I haven't done an rpi-update and looked myself, and the commit doesn't say.

It would be the most logical one out of under-voltage and over-temp (yellow or red). 

Finally on the subject of icons, in the past if your Pi was working particularly hard, you might have noticed some yellow and red squares appearing in the top-right corner of the screen, which were indications of overtemperature or undervoltage. These have now been replaced with some new symbols that make it a bit more obvious what’s actually happening; there’s a lightning bolt for undervoltage, and a thermometer for overtemperature. 

pi@raspberrypi:~ $ vcgencmd get_throttled

throttled=0x50000 

pi@raspberrypi:~ $ sudo apt-get install stress stress-ng

pi@raspberrypi:~ $ stress-ng --cpu 4 --io 1 --vm 1 --vm-bytes 128M --timeout 10s --verbose 

Search "avoid_warnings" (1 hit in 1 file)

  D:\Download\linux-rpi-4.9.y\drivers\gpu\drm\vc4\Kconfig (1 hit)

config DRM_VC4

tristate "Broadcom VC4 Graphics"

depends on ARCH_BCM2835 || COMPILE_TEST

depends on DRM

depends on SND && SND_SOC

depends on COMMON_CLK

select DRM_KMS_HELPER

select DRM_KMS_CMA_HELPER

select DRM_GEM_CMA_HELPER

select DRM_PANEL

select SND_PCM

select SND_PCM_ELD

select SND_SOC_GENERIC_DMAENGINE_PCM

select DRM_MIPI_DSI

help

  Choose this option if you have a system that has a Broadcom

  VC4 GPU, such as the Raspberry Pi or other BCM2708/BCM2835.

  This driver requires that "avoid_warnings=2" be present in

  the config.txt for the firmware, to keep it from smashing

  our display setup. 

Red power LED is blinking

A blinking red power LED indicates problems with the power supply. On model A and B, it is hard-wired to the 3.3V power supply rail. If it is blinking, as one user has reported^[1] it means the 5V power supply is dropping out. Use a different power supply.

On model B+ (and presumably also the A+), the circuit has been improved to give a much more reliable warning of poor power quality. The red power LED is wired to an APX803 supervisor^[2] which kicks in when the 5V power supply drops below 4.63V^[3]. If it does, the LED will blink. Check your connections, cable, and power supply.

The Raspberry Pi 2 has a 2.2 amp polyfuse which limits the power which may be supplied via the microUSB socket. This is more than enough to power the Pi and the USB sockets.

Initially the USB sockets can only draw 600 mA. At worst this leaves 1.6 amps for the Pi2 and anything connected to the gpios.

By changing a setting after boot software can configure the USB sockets to draw up to 1.2 amps. At worst this leaves 1 amp for the Pi2 and anything connected to the gpios.

You haven't mentioned connecting anything to the gpios or the USB.

The only meaning to the rainbow square in the top right of the screen is that the 5V line has dropped beneath 4.65V.

If you trust the power supply to be accurate the other cause of low voltage is thin wires in the microUSB cable. 

It provides a means of recovering from, e.g.

• too high an overclock
• a typo in cmdline.txt
• an incorrect kernel=<filename> parameter
• an invalid display mode

without requiring a PC. (Obviously it won't help if you've deleted start.elf...) 

Connect pins 5 & 6 with a jumper or piece of wire.

If you are using these pins for your own purposes and want to avoid ending up in safe mode, add this to config.txt:

avoid_safe_mode=1

Installing the software

If the master is not a Raspberry Pi then just install ffmpeg or avconv on your machine. 

What you need

Firstly, you need to get a few things in order for your video wall to work and to avoid messing up your network. Here is the list of required hardware:

• A Yodeck player for each screen of the video wall
• Another Yodeck player (as “Master”) that will play back the actual content
• An HDMI-to-IP video streamer – we recommend Lenkeng LKV373A (sender only, costs about $36)
• A Network router – no special specs, just having a LAN and a WAN port will do
• One Network switch to connect all of the above 

The Raspberry Pi is equipped with one SPI bus that has 2 chip selects. 

Unfortunately, there is no schematic, however wiring is pretty simple:

LCD0      - RPi

SDO(MISO) - MISO/GPIO9, pin21 (common)

LED       - 5V through 1k resistor, pin 2 (common)

SCK       - CLK/GPIO11, pin23 (common)

SDI(MOSI) - MOSI/GPIO10, pin19 (common)

D/C       - GPIO24, pin18

RESET     - GPIO25, pin22

CS        - CE0/GPIO8, pin24

GND       - GND, pin 6 (common)

VCC       - 3.3V, pin 1 (common)

LCD1      - RPi

SDO(MISO) - MISO/GPIO9, pin21 (common)

LED       - 5V through 1k resistor, pin 2 (common)

SCK       - CLK/GPIO11, pin23 (common)

SDI(MOSI) - MOSI/GPIO10, pin19 (common)

D/C       - GPIO18, pin12

RESET     - GPIO23, pin16

CS        - CE1/GPIO7, pin26

GND       - GND, pin 6 (common)

VCC       - 3.3V, pin 1 (common)