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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. 

Thus, a new format was created for these in the CHD file. Compressed Hunks of Data, or CHD for short, are designed very specifically around the needs of mass storage media. Some arcade games, consoles, and PCs will require a CHD to run. As CHDs are already compressed, they should NOT be stored in a ZIP or 7Z file as you would for ROM images. 

Why do my Neo Geo ROMs no longer work? How do I get the Humble Bundle Neo Geo sets working? 

Recently the Neo Geo BIOS was updated to add a new version of the Universal BIOS. This was done between 0.171 and 0.172, and results in an error trying to load Neo Geo games with an un-updated neogeo.zip set. This also affects the Humble Bundle set: the games themselves are correct and up to date as of MAME 0.173 (and most likely will remain so) though you’ll have to pull the ROM set .ZIP files out of the package somehow yourself. However, the Neo Geo BIOS set (neogeo.zip) included in the Humble Bundle set is incomplete as of the 0.172 release of MAME. We suggest you contact the provider of your sets (Humble Bundle and DotEmu) and ask them to update their content to the newest revision. If enough people ask nicely, maybe they’ll update the package. 

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

recalboxOS uses many awesome existing components, like EmulationStation2 as frontend, piFBA and Retroarch as emulators, RaspberryPI NOOBS as installation/recovery system.