Raspberry Pi: Booting Problem
On the Raspberry Pi board, there is only a Boardcom BCM2385
multimedia processor, and there is no
other built in software to boot up the Raspberry Pi board. For the BCM2835 SoC,
there is only a small first stage bootloader, stored in the ROM of the BCM2835
SoC, to initiate the boot up processes of the Raspberry Pi board by loading some
BLOB from the SD card. And therefore, there is also no display output before the Raspberry Pi
boots successfully. Apart from the hardware problem, the booting problem of a
Raspberry Pi board are mainly caused by the loading of BLOB.
LED status
The five LEDs near the USB connector
are important status displays of Raspberry
Pi board. The booting status of the Raspberry Pi board can also obtained the
status of these LEDs. The meanings of LED indicators on the Raspberry Pi board version 2
model B are
LED Part Name |
LED Color |
Indication |
LED Status of Display |
ACT |
Green |
SD card Activity |
blinking during SD card activity |
PWR |
Red |
3.3V Powered on |
on: 3.3V power is present; off: 3.3V power is off |
FDX |
|
Full duplex LAN connected |
on: Full duplex Ethernet connected; off: half duplex Ethernet connected |
LNK |
|
Link of LAN activity |
on: Ethernet connected; off: Ethernet disconnected |
100 |
|
100 Mbps LAN connected |
on:100 Mbps; off:10 Mbps |
For reference, the meanings of LED indicators on the Raspberry Pi board version
1 model B are.
LED Part Name |
LED Color |
Indication |
LED Status of Display |
OK |
Green |
|
|
PWR |
Red |
|
|
FDX |
|
|
|
LNK |
|
|
|
10M |
|
|
|
PWR
LED
The red power LED is hard-wired to the 3.3V output rail from the 3.3V voltage
regulator of +5V0. The PWR LED only indicate that the Raspberry Pi is powered
with a power supply, which is high enough to turn on the PWR LED wired to the
3.3V rail on the microUSB socket. In order to have a normal boot up, the red PWR
LED must be in steady on state, that is the Raspberry Pi is powered normally. If
the red PWR LED does not light, the Raspberry Pi may be not connected properly.
And when the red PWR LED is blinking, the 5V microUSB power supply may be
unstable.
Therefore if PWR LED is off or is not in normal steady on state, then check the
power supply first.
ACT
LED
The ACT LED is hard-wire to a GPIO pin and is designed as an indicator of the SD
card activity of by default. When the Raspberry Pi board is powered on, the
BCM2835 SoC will first reset the chip to the default state by itself. After the
chip reset stage, the GPIO pin will be reset as input port using a pull-down
resistor. The ACT LED will be turned off also, however the voltage pontential
due to the pull-down resistor may provide a tiny amount of current running
through the ACT LED and cause a steady faintly glowing ACT LED. Therefore a
faintly glowing or off ACT LED indicates that no BLOB is loaded from the SD
card.
Since there is no built in software to boot up the Raspberry Pi board, a small
first stage bootloader, stored in the ROM of the BCM2835 SoC, is used to
initiate the boot up processes of the Raspberry Pi board by loading some BLOB
from the SD card after the chip reset when the Raspberry Pi board is powered on
by default. As an indicator of the SD card activity, there are some pattern
defined to indicate the activity of SD card. The patterns are as follow
ACT
LED Pattern |
Fireware before |
For fireware since 20th October 2012, loader.bin is merged into bootcode.bin |
off |
bootcode.bin not loaded. No code is loaded from SD card |
faintly glowing |
1 flash |
Note: May be a Paapberry Pi from Micron, i.e. M with an orbit on the processor.
Using software since Sept 2013 and a SD card with capacity 4Gb, a 2Gb SD card
doesnot work Raspberry Pi from Micron. |
3 flashes |
loader.bin not found |
start.elf not found |
4 flashes |
loader.bin not launch-able or loader.bin corrupt |
start.elf not launch-able |
5 flashes |
start.elf not found |
|
6 flashes |
start.elf not launch-able |
|
7 flashes |
kernel.img not found |
kernel.img not found |
8 flashes |
|
SDRAM not recognized. Newer bootcode.bin/start.elf firmware is needed. |
Blinking |
kernel.img is read from the SD card successfully. |
Therefore if the power supply of the Raspberry Pi is assured and no blinking ACT
LED pattern is observed during booting, then there may be a booting problem.
Check the corresponding file on the SD card as indictated by the ACT LED
flashing pattern. However, if there is a short blinking ACT LED and there is
nothing on display, then the problem may not be a booting problem, or the
problem may be a display connection problem related to the software display
configuration, the display connection, or the display.
Booting Problem
In general, the booting problem may be caused by
- Power supply: There are many reasons that cause the Raspberry Pi not to boot
with a working power supply. The PWR LED only indicates that there is a power supply.
A reliable and correct 5V power supply should be used to ensure the Raspberry Pi
board has a stable 5V supply at the microUSB power input socket.
- Low quality power supply with a lower voltage output than the rated output
voltage 5V.
- Unsuitable power supply with output rating of insufficient capacity to delivery
sufficient current supply to the Raspberry Pi board and its peripheral. e.g.
750mA for model B or 400mA for model A at 5V
- Low quality microUSB cable may cause a large voltage drop of the power supply at
the microUSB plug. For a very long connection cable with a very thin copper
wire, the supplied voltage at the microUSB socket may be out of the
specification required by the Raspberry Pi board, i.e. a voltage between 4.75V
and 5.25V.
- Too much devices are attached to the Raspberry Pi board and more current
are drawn from the power supply. If the current drawn is reasonably high, then
it is possible to cause a voltage drop along the lines from the power supply to
the items being powered.
- The F3 polyfuse of the Raspberry Pi could be blown by doing something wrong
before. A polyfuse can take a very long time to recover. The recovery time may
be some days or weeks.
- SD card: There are many reasons that cause the Raspberry Pi not to boot with a
working SD card.
- Poor contact between SD card slot and the SD card may
be caused by a damaged SD card slot which cannot hold an SD card in place
properly, deformed spring contact inside the SD card holder, or deformed SD
card.
- Some SD cards are not compatible with the Raspberry Pi. If the SD card doesnot
work with the latest software package, then try another card.
- Software: There are many reasons that cause the Raspberry Pi not to boot with a
prepared SD card apparting from the hardware itself.
- The old software package with the old firmware can
boot up the Raspberry Pi with known peripherals only, a new Raspberry Pi might
using a new type of RAM that the firmware of the older software package not
supported. So try to use the latest version software package for a new Raspberry
Pi board. For some newer software package, a
8 flashes pattern on the ACT LED is used to indicate that the
SDRAM is not recognized
- Sometimes the SD card are not prepared correctly especially if the SD card has
been used before. Using the SDFormatter from sdcard.org to prepare a resizable
SD card and following the NOOBS method to create a SD card provide a simpler way
to create an used SD card for Raspberry Pi. Or try with a new pre formatted SD
card.
- If the SD card cannot be used to boot up the Raspberry Pi after a successful
boot, files stored in the SD card may be corrupted during last improper
shutdown. Using the NOOBS recovery mode to restore the operating system or
reinstall the operating system again. A shutdown procedure may help to shutdown
the operating system properly before switching off the Raspberry Pi. e.g type
"sudo shutdown -h now" to do a proper shutddown in Raspbian.
- Display: There are many reasons that cause nothing on display after the
Raspberry Pi bootup .
- Nothing on display may be due to the connection of
display to the wrong display output port of the Raspberry Pi. By default, the
digital HDMI display output port is defined as the active port and the output
signal is normal HDMI mode. And therefore a display connected to the composite
RCA output port or the display does not support the default HDMI output mode.
For the NOOBS package, if the Raspberry Pi is bootup, then this may be corrected
by pressing "shift" key after the Raspberry Pi is powered to enter the recovery
mode and try pressing key "2" to "HDMI safe mode", key "3" or "4" to composite
mode. Otherwise, the Raspberry Pi may be in the case of "not to boot"
- Sometimes, a long poor quality video cable may also cause unstable or loss of
signal.
- Besides, the using of unsuitable video converter or adapter, display mode may
also cause nothing on display. Try another display to ensure the Raspberry Pi is
bootup.